Physical and Chemical Changes, Solution: notes and MCQs for State PSC

Physical and Chemical Changes, Solution is part of Chemistry. Below are notes on 11 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Concept of Solutions: Solute, Solvent, and Components

A solution is a homogeneous mixture of two or more components.
Solute: Component present in a smaller amount.
Solvent: Component present in a larger amount, determining the physical state of the solution.
Tincture of iodine is a solution of iodine (solute) in alcohol (solvent).
Mole fraction (X) of a component = Moles of component / Total moles in the solution.
Number of moles = Given mass / Molar mass.
Number of molecules is directly proportional to the number of moles.
Solutions are classified by their ability to conduct electricity:

Electrolytes: Conduct electricity due to mobile ions (e.g., copper sulphate, sodium chloride, potassium chloride, sodium hydroxide, HCl, KOH).
Strong Electrolytes: Dissociate completely into ions (e.g., potassium chloride, NaCl, HCl, KOH).
Non-electrolytes: Do not conduct electricity as they do not form ions (e.g., sugar solution, glucose solution).

Water is a good solvent for ionic compounds and polar substances (e.g., glucose, urea, acetone) due to its high dipole moment (polarity) and high dielectric constant.
Sugar dissolves in water primarily due to the formation of hydrogen bonds.
Reverse osmosis is a process used for transforming salty water into pure water.
Colligative properties of dilute solutions depend only on the number of solute particles, not their chemical nature or size.
Adding common salt (a non-volatile solute) to water increases its boiling point (boiling point elevation) and decreases its freezing point (freezing point depression).
Glass is best described as a supercooled solution (an amorphous solid with high viscosity).
On calibrated pipettes:

TD means "To Deliver" (the specified volume).
TC means "To Contain" (the specified volume).

Pasture pipettes are commonly used for transferring small volumes of liquids (< 5 mL).
Safety Data Sheets (SDS) contain 16 standardized sections.
Flammable gases should be stored at a minimum distance of 20 feet from oxygen.
The Van't Hoff factor (i) for an electrolyte is generally greater than one due to dissociation into multiple ions.
The Ideal Gas Equation is PV = nRT.
Air is always a mixture of various gases.

Definition and Characteristics of Chemical Changes (Chemical Reactions)

Chemical Change (Chemical Reaction): A process where substances are transformed into new substances with different chemical compositions and properties.
Characteristics of Chemical Changes:

Formation of one or more new substances.
Often irreversible or difficult to reverse.
Accompanied by significant energy changes (heat, light, sound produced or absorbed).
Examples: Burning (paper, magnesium ribbon, coal, glucose), rusting of iron, milk turning sour, cooking food, fermentation, mixing acid and base, rancidity.

Physical Change: A change in the physical properties (e.g., state, shape, size) of a substance, without altering its chemical composition or forming new substances.
Characteristics of Physical Changes:

No new substances formed.
Generally reversible.
Minimal energy changes.
Examples: Melting ice, boiling water, dissolving sugar/salt, magnetization, cutting hair/fruit/foil, evaporation, sublimation of camphor.

Types of Chemical Reactions:

Combination Reaction: Two or more reactants combine to form a single product (e.g., CaO + H₂O → Ca(OH)₂, 2Mg + O₂ → 2MgO).
Decomposition Reaction: A single compound breaks down into two or more simpler substances (e.g., CaCO₃ → CaO + CO₂, 2HgO → 2Hg + O₂, Electrolysis of water, 2AgCl → 2Ag + Cl₂ in sunlight). Thermal decomposition can apply to ZnO, Ag₂O.
Displacement (Substitution) Reaction: A more reactive element displaces a less reactive element from its compound (e.g., Fe + CuSO₄ → FeSO₄ + Cu; Iron is more reactive than copper. Pb + CuCl₂ → PbCl₂ + Cu).
Double Displacement Reaction: Exchange of ions between two compounds, often leading to precipitation (e.g., Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl).
Redox (Oxidation-Reduction) Reactions: Involve simultaneous oxidation and reduction.

Oxidation: Gain of oxygen, loss of hydrogen, loss of electrons, increase in oxidation state.
Reduction: Loss of oxygen, gain of hydrogen, gain of electrons, decrease in oxidation state.
Oxidizing Agent: Causes oxidation (gets reduced itself).
Reducing Agent: Causes reduction (gets oxidized itself).
Examples: Combustion (e.g., CH₄ + 2O₂ → CO₂ + 2H₂O, where Carbon is oxidized), rusting, rancidity, 2Mg + O₂ → 2MgO, ZnO + C → Zn + CO (C is reducing agent, ZnO is oxidizing agent).

Stoichiometry & Laws of Chemical Combination:

Law of Conservation of Mass: Matter cannot be created or destroyed in a chemical reaction; total mass of reactants equals total mass of products (e.g., 10g CaCO₃ decomposed to 5.6g CaO produces 4.4g CO₂).
Law of Constant (Definite) Proportion: A given compound always contains its component elements in fixed ratios by mass (e.g., Ammonia always has the same N:H proportion).
Avogadro's Hypothesis: Equal volumes of different gases at the same temperature and pressure contain equal numbers of molecules.
Glucose Combustion: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O; 1 mole of glucose requires 6 moles of oxygen.

Reaction Rate & Catalysis:

Reaction Rate: Generally decreases with time as reactant concentrations decrease.
Factors Influencing Reaction Rate: Temperature (higher temperature increases rate due to more rapid molecular motion), concentration of reactants, presence of catalyst, surface area of reactants/catalyst.
Catalyst: A substance that changes (usually increases) the rate of a chemical reaction without being consumed; it works by lowering the activation energy of the reaction.
Catalytic Promoter: Increases the activity of a catalyst.
Catalytic Inhibitor: Slows down or stops a reaction.
Surface Area of Catalyst: Higher surface area (e.g., powdered form) leads to higher catalytic activity.
Enzyme Catalysis: Biological catalysts, often act as homogeneous catalysts (in solution) and function via an 'induced fit' mechanism.
Rate Constant (k): Depends on temperature (Arrhenius concept); defined as the reaction rate when each reactant's concentration is unity; unit for a first-order reaction is s⁻¹.

Solutions & Hard Water:

Hard Water: Water containing significant concentrations of dissolved metallic ions.
Metallic Constituents of Hard Water: Primarily Calcium (Ca²⁺) and Magnesium (Mg²⁺) ions. Iron (Fe²⁺/Fe³⁺) also contributes.
Temporary Hardness: Caused by dissolved bicarbonates of Ca and Mg; can be removed by boiling.
Permanent Hardness: Caused by dissolved chlorides and sulfates of Ca and Mg; cannot be removed by boiling.
Disadvantages of Hard Water: Not suitable for drinking, washing clothes (forms scum with soap), or use in boilers (forms scale).

Desiccants/Drying Agents: Substances that absorb moisture (exhibit hygroscopic nature). Example: Silica gel.
Fire Extinguishers: Carbon dioxide (CO₂) and Bromochlorodifluoromethane (BCF) are common.
Fermentation: A process where organic compounds are slowly decomposed into simpler substances, typically in the absence of oxygen (anaerobic).
Corrosion (e.g., Rusting): A chemical reaction (oxidation) where a metal reacts with its environment. During rusting of iron, the weight of iron increases due to the incorporation of oxygen.
Precipitation Reaction: A reaction where an insoluble solid (precipitate) forms when two solutions are mixed.
Egg Boiling: A chemical change (protein denaturation) leading to a decrease in disorder and a negative ΔG (spontaneous process).
Air: Is always a mixture.
Glass Etching: Can be achieved using diamond or hydrofluoric acid (HF).
Nanomaterials Hindrance: Prone to coarsening effect from Ostwald ripening or agglomeration on aging.
Chemical Equilibrium: A dynamic state where the rates of forward and backward reactions are equal, resulting in no net change in reactant and product concentrations. Catalysts help reach equilibrium faster but do not shift its position.
Adsorbate: A substance that is deposited or held on the surface of another substance (adsorbent).

Definition and Characteristics of Physical Changes

Physical Change Definition: Alters the form or state (e.g., solid, liquid, gas) of a substance, but its chemical composition and identity remain the same; no new substance is formed.
Physical Change Characteristics:

The chemical identity of the substance remains unchanged.
No new chemical bonds are formed or broken.
Often reversible (e.g., melting ice to water and freezing water back to ice).
Energy changes involved are typically smaller compared to chemical changes.

Examples of Physical Changes:

Melting of ice, wax, or other solids (note: melting of wax is physical, but burning a candle involves both physical and chemical changes).
Boiling or evaporation of water.
Condensation of steam.
Freezing of water.
Dissolution of sugar in water.
Heating of a platinum crucible.
Sublimation of substances like camphor, naphthalene, ammonium chloride, or anthracene.
Deposition (change of gaseous state directly to solid state).

States of Matter: Generally considered 5 states: Solid, Liquid, Gas, Plasma, and BoseEinstein Condensate.
Intermolecular Forces:

The force of attraction among molecules is highest in solids (e.g., sugar) and lowest in gases (e.g., helium).
The melting point of a solid is an indication of the strength of the intermolecular forces of attraction.

Phase Changes (Physical Processes):

Melting/Fusion: Solid to liquid at a specific melting point.
Boiling: Liquid to gas (a bulk phenomenon, occurring at the boiling point throughout the liquid); bubbles in vigorously boiling pure water are composed primarily of water vapour.
Evaporation: Liquid to gas (a surface phenomenon, occurring below the boiling point).
Sublimation: Solid directly to gas without changing into the liquid state (e.g., naphthalene, camphor, ammonium chloride, anthracene).
Deposition: Gas directly to solid without changing into the liquid state.
Condensation: Gas to liquid.
The state of matter can be changed by altering its temperature and/or pressure.

Separation Techniques (based on physical properties):

Sublimation: Separates a sublimable solid (e.g., naphthalene, camphor, anthracene) from non-sublimable substances (e.g., sand, salt).
Distillation: Separates liquids with different boiling points, or a nonvolatile dissolved solid from a liquid.
Chromatography: Separates components based on their differential distribution between a stationary and a mobile phase (e.g., colors from a dye, pigments from natural colors, drugs from blood). It cannot separate radioisotopes.
Filtration: Separates insoluble solids from liquids.
Evaporation: Separates a soluble nonvolatile solid from its volatile solvent.

Other Relevant Physical Concepts:

Diffusion: The intermixing of particles of two different types of matter on their own.
Crystalline Solid: Possesses a regular, ordered arrangement of particles (e.g., table salt).
Distilled Water: Considered pure and free from impurities.
Nanomaterials:

Their properties strongly depend on the surface atoms.
They have a large surface area to volume ratio.
Nanoparticles typically have sizes < 100 nm.
Particles of nanomaterials cannot be seen with the naked eye.

Boyle's Law: At a constant temperature, the volume (V) of a fixed mass of gas is inversely proportional to its pressure (P), mathematically represented as V $\propto$ 1/P, V = K/P, or VP = K.
Compressed Air Technique: Used for cleaning and drying documents.

Distinction between Physical and Chemical Changes

Physical Change: A change where no new substance is formed, and the chemical composition remains the same.
Physical changes are generally reversible.
Examples of physical changes include: melting, freezing, boiling, condensation, sublimation (e.g., heating camphor, solid carbon dioxide), dissolution (e.g., sodium chloride in water, CO₂ in water), crystallization (e.g., sodium chloride), magnetization of iron, tempering of iron, conversion of iron to an electromagnet, and changes in state, shape, or size.
Water in its various states (ice, liquid, steam) is a compound and a pure substance; its change between states is a physical change.
Chemical Change: A change where one or more new substances are formed, and the chemical composition is altered.
Chemical changes are usually irreversible.
Examples of chemical changes include: burning (e.g., candle, coal, paper), rusting of iron, cooking of food, ripening of fruits, curdling of milk, souring of milk, and digestion of food.
Rusting of iron is a chemical change, forming iron oxide (Fe₂O₃.nH₂O), which can be prevented by coating with zinc (galvanization).
The burning of a candle involves both physical (wax melting) and chemical (wax burning to produce carbon dioxide and water vapor) changes.
Pure Substances: Have a fixed chemical composition and distinct properties. They can be elements (e.g., Iron, Mercury, Bromine) or compounds (e.g., Water, Sugar, Sodium Chloride, Chalk).
Mixtures: Consist of two or more pure substances physically combined in variable proportions. Components retain their individual properties and can be separated by physical means.
Examples of mixtures include: Air, Soil, Sea Water, Milk, Gasoline, Ice-cream, Honey, Brine, Tea, Coffee.
Air is a mixture of gases, primarily nitrogen and oxygen.
Brine (saltwater) is a mixture that leaves a solid residue (salt) upon heating due to evaporation of water.
Separation Techniques for Mixtures (Physical Processes):
Evaporation: Separates a non-volatile soluble solid from its liquid solvent (e.g., sodium chloride from water).
Sublimation: Separates a solid that sublimes (changes directly from solid to gas) from a non-sublimable solid (e.g., camphor from solid sodium chloride).
Chromatography: Separates components based on differential adsorption or solubility (e.g., pigments from flower petals extract, dyes in black ink).
Distillation: Separates liquids with different boiling points (e.g., acetone and water mixture) or a non-volatile solid from a liquid (e.g., pure water from impurities). It is generally not used for purification of solid impurities themselves.
Centrifugation: Separates denser components from lighter ones using centrifugal force (e.g., butter from cream).
Filtration: Separates insoluble solids from liquids (part of water purification).
Water Purification (for civil supplies): Often involves both filtration (physical) and chlorination (chemical, for disinfection).

Distinguishing Solutions, Colloids, and Suspensions

True Solution: Homogeneous mixture; particle size < 1 nm; transparent; stable; particles do not settle; do not show Tyndall effect; cannot be separated by filtration. E.g., Sugar in water, Salt in water, Air, Alloys (Brass), Alcohol in water, Sulphur in carbon disulphide, Tincture of iodine, Hydrochloric acid, Vinegar, Soda water.
Colloid: Heterogeneous mixture (appears homogeneous); particle size 1-100 nm (nanoparticle range); translucent; stable; particles do not settle; show Tyndall effect (scatter light); particles undergo Brownian motion; cannot be separated by ordinary filtration but by ultrafiltration or dialysis. E.g., Milk, Jelly, Fog, Smoke, Butter, Cheese, Froth, Blood, Shaving cream, Mud (sol).
Suspension: Heterogeneous mixture; particle size > 100 nm; opaque; unstable; particles settle down over time; show Tyndall effect; can be separated by filtration. E.g., Muddy water, Sand in water.
Types of Colloids (Dispersed Phase DP / Dispersing Medium DM):

Aerosol: DP Solid/Liquid, DM Gas. E.g., Smoke (Solid in Gas), Fog/Mist (Liquid in Gas).
Foam: DP Gas, DM Liquid. E.g., Shaving cream, Froth. (Dispersing medium is liquid).
Emulsion: DP Liquid, DM Liquid. E.g., Milk (fat droplets in water), Butter (water in oil).
Sol: DP Solid, DM Liquid. E.g., Mud, Paints. (Dispersing medium is liquid).
Gel: DP Liquid, DM Solid. E.g., Jelly, Butter (DM is solid).

Centrifugation: Separation technique for very small insoluble particles or colloidal particles from a liquid (solid-liquid mixtures); used for separating cream from milk.
Alum (Coagulation/Flocculation): Used to clean muddy water by causing small suspended particles to clump together and settle.
Separation Techniques:

Distillation: Separates miscible liquids with sufficient difference in boiling points (e.g., Acetone and water).
Fractional Distillation: Separates miscible liquids with close boiling points (e.g., Kerosene and petrol).
Separating Funnel: Separates immiscible liquids (e.g., Water and kerosene oil, Benzene and water).
Chromatography: Separates components based on differential adsorption; used for colored components (e.g., Dye in black ink, Pigments from plant extract).
Reverse Osmosis (RO): Desalination; converts sea water into pure water by removing dissolved salts.

Water Purification Methods:

Aeration followed by filtration: Removes iron.
Filtration through activated carbon: Removes color and odor.
Treatment with UV light: Removes microorganisms.
Reverse Osmosis: Removes excess salts.

Mixtures & Substances:

Homogeneous Mixture: Uniform composition (e.g., True solutions, Air, Alloys).
Heterogeneous Mixture: Non-uniform composition (e.g., Suspensions, Colloids, Oil in water, Soil).
Substance (Pure): Cannot be separated by physical means (e.g., Tin, Boric acid, Urea).

Gas Properties:

Distance between gas molecules increases on increasing container volume or on leakage of gas from the container.
Graham's Law of Effusion: Rate of effusion is inversely proportional to the square root of molar mass; lighter gases effuse faster (N2 will effuse faster than O2).

Glass: Non-crystalline amorphous solid; also known as a supercooled liquid.

Energy Changes in Chemical Reactions (Exothermic and Endothermic Processes)

Chemical Energy: Energy stored within the bonds of chemical substances.
Enthalpy (H): The total heat content of a system at constant pressure. Change in enthalpy (ΔH) represents heat absorbed or released during a reaction.
Exothermic Reactions:

Release energy (typically heat) to the surroundings.
ΔH is negative (ΔH < 0).
Examples: Combustion (burning of carbon, natural gas, methane), reaction of quick lime (CaO) with water (producing slaked lime), dilution of strong acids (e.g., sulphuric acid), respiration, decomposition of vegetable matter into compost, formation of magnesium oxide (Mg + O₂ → MgO).

Endothermic Reactions:

Absorb energy (typically heat) from the surroundings.
ΔH is positive (ΔH > 0).
Examples: Decomposition reactions (e.g., CaCO₃ → CaO + CO₂, decomposition of silver chloride by sunlight), photosynthesis, evaporation of water, sublimation of camphor, melting of ice.

Gibbs Free Energy (G): A thermodynamic potential that determines the spontaneity of a process at constant temperature and pressure.
Spontaneity of Reactions:

A reaction is spontaneous if the change in Gibbs Free Energy (ΔG) is negative (ΔG < 0).
Gibbs-Helmholtz Equation: ΔG = ΔH TΔS, where T is absolute temperature and ΔS is change in entropy.
Conditions for Spontaneity based on ΔH and ΔS:

ΔH < 0, ΔS > 0: Always spontaneous (ΔG < 0 at all T).
ΔH > 0, ΔS < 0: Never spontaneous (ΔG > 0 at all T).
ΔH < 0, ΔS < 0: Spontaneous at low temperatures (T < ΔH/ΔS).
ΔH > 0, ΔS > 0: Spontaneous at high temperatures (T > ΔH/ΔS).

Threshold Temperature (Teq): The temperature at which ΔG = 0, calculated as Teq = ΔH/ΔS. This marks the transition point between spontaneous and non-spontaneous conditions.
Example (from MCQ): For a reaction with ΔH° = -90 kJ/mol and ΔS° ≈ -0.1648 kJ/mol·K, Teq ≈ 546 K. The reaction is spontaneous for T < 546 K.

Electromotive Force (EMF) and Spontaneity:

For a chemical (galvanic) cell, ΔG = nFEcell (where n is moles of electrons, F is Faraday constant, Ecell is EMF).
A positive EMF (Ecell > 0) indicates a spontaneous reaction (ΔG < 0).

Methods of Expressing Concentration of Solutions (Mass Percentage, Volume Percentage, Molarity, Molality, Parts Per Million)

Percentage,

Volume

Percentage, Molarity, Molality, Parts Per

Million)

Concentration: Amount of solute present per unit volume or per unit mass of the solution/ solvent.
Mass Percentage (% w/w):

`Mass % = (Mass of solute / Mass of solution) × 100`
`Mass of solution = Mass of solute + Mass of solvent`
Temperature-independent.

Volume Percentage (% v/v):

`Volume % = (Volume of solute / Volume of solution) × 100`
Used for liquid-liquid solutions.
Temperature-dependent.

Mass-Volume Percentage (% w/v):

`Mass-Vol % = (Mass of solute (g) / Volume of solution (mL)) × 100`
Temperature-dependent.

Molarity (M):

`M = Moles of solute / Volume of solution (L)`
Unit: mol/L or M.
Temperature-dependent (volume changes with temperature).

Molality (m):

`m = Moles of solute / Mass of solvent (kg)`
Unit: mol/kg or m.
Temperature-independent (mass does not change with temperature).

Parts Per Million (PPM):

`PPM = (Mass of solute / Mass of solution) × 10^6` (for mass-based)
`PPM = (Volume of solute / Volume of solution) × 10^6` (for volume-based)
Used for very dilute solutions (e.g., pollutants).

Normality (N):

`N = Number of gram equivalents of solute / Volume of solution (L)`
`N = Molarity × n-factor` (n-factor = valence factor, e.g., for H₂SO₄, n=2).
Temperature-dependent.

Properties of Colloids (Tyndall Effect, Brownian Motion)

Colloids are heterogeneous mixtures with particle sizes between 1 nm and 1000 nm, appearing homogeneous to the naked eye.
They are generally stable and do not settle down when left undisturbed.
Tyndall Effect:

The scattering of a beam of light by colloidal particles, making the path of light visible (Tyndall cone).
Requires particle diameter not significantly smaller than the wavelength of light and a difference in refractive indices between dispersed phase and dispersion medium.
Exhibited by colloidal solutions (e.g., milk, starch solution, fog).
NOT exhibited by true solutions (e.g., sugar solution, lime juice, isotonic solutions) because their particles are too small to scatter light.

Brownian Motion:

Continuous, random, zigzag motion of colloidal particles.
Caused by the unequal bombardment of colloidal particles by molecules of the dispersion medium.
Contributes to the stability of colloids by preventing them from settling.

Colloidal particles carry an electric charge (positive or negative).
Electrophoresis: The movement of charged colloidal particles towards an oppositely charged electrode under the influence of an electric field.
Coagulation (or Flocculation): The process by which colloidal particles aggregate and settle down.

Occurs by adding electrolytes whose ions carry a charge opposite to that of the colloidal particles.
Example: Alum (containing Al³⁺ ions) is used to stop bleeding because blood is a negatively charged colloidal system, and Al³⁺ ions cause its coagulation.

Types of Colloids and Examples:

Sol: Solid dispersed in liquid (e.g., Paint, Cell fluid/Hydrosol).
Emulsion: Liquid dispersed in liquid (e.g., Milk).
Gel: Liquid dispersed in solid (e.g., Butter, Cheese).
Aerosol: Liquid in gas (e.g., Fog, Cloud) or Solid in gas (e.g., Smoke).

Saturated, Unsaturated, and Supersaturated Solutions

An Unsaturated Solution contains less solute than the maximum amount that can be dissolved at a given temperature and pressure; more solute can be dissolved.
A Saturated Solution contains the maximum amount of solute that can be dissolved at a given temperature and pressure; it exists in dynamic equilibrium with any undissolved solute.
A Supersaturated Solution contains more dissolved solute than a saturated solution at the same temperature and pressure; it is unstable and prone to precipitation of excess solute upon disturbance.
Colligative Properties of Solutions (properties dependent on solute particle concentration, not identity):

Vapour Pressure Lowering: The vapour pressure of a solution is lower than that of the pure solvent at the same temperature.
Boiling Point Elevation: The boiling point of a solution is higher than that of the pure solvent.
Freezing Point Depression: The freezing point of a solution is lower than that of the pure solvent.
Osmotic Pressure: The pressure that must be applied to a solution to prevent the net flow of solvent across a semi-permeable membrane into the solution. Applying pressure to the solution can prevent water movement.
Water Potential: Addition of solutes to a solution decreases its water potential.

Solubility and Factors Affecting Solubility (Temperature, Pressure)

Solubility is the maximum amount of a solute that can dissolve in a given amount of solvent at a specific temperature and pressure.
Effect of Temperature on Solubility:

For most solids in liquids, solubility increases with increasing temperature.
For gases in liquids, solubility generally decreases with increasing temperature.

Effect of Pressure on Solubility:

Pressure has negligible effect on the solubility of solids and liquids in liquids.
For gases in liquids, solubility increases with increasing pressure (Henry's Law). Example: Carbon dioxide (CO2) in soda water. Opening a soda bottle reduces pressure, releasing CO2.

Water as a Solvent:

Water is a "universal solvent" due to its dipolar (polar) nature, which allows it to dissolve many ionic and polar substances ("like dissolves like").

Colligative Properties (Effect of Non-volatile Solutes):

Adding a non-volatile solute (e.g., salt) to pure water:

Increases its boiling point (Boiling Point Elevation).
Decreases its freezing point (Freezing Point Depression).

Example: Sea water (high solute concentration) has a lower freezing point and higher boiling point than tap water, which in turn has a lower freezing point and higher boiling point than distilled water (pure). Thus, distilled water solidifies first.

Effect of Volatile Solutes:

Adding a volatile, miscible liquid (e.g., methyl alcohol) to water can decrease the boiling point of the resulting mixture (e.g., by forming a lowerboiling azeotrope).

Water Hardness:

Hardness of water is caused by the presence of dissolved salts of Calcium (Ca) and Magnesium (Mg).
Temporary hardness is caused by bicarbonates of calcium and magnesium (e.g., Calcium bicarbonate).
Permanent hardness is caused by chlorides and sulphates of calcium and magnesium.

Separation Techniques:

Reverse Osmosis: Used for desalination. Requires applying pressure larger than the osmotic pressure to force solvent (water) from a higher solute concentration (seawater) to a lower one (pure water).
Paper Chromatography: Based on the principles of Partition (differential distribution of components between stationary and mobile phases) and Solubility.
Solvent Extraction: Based on Nernst's Distribution Law (Partition Law), which describes the equilibrium distribution of a solute between two immiscible solvents.
Vacuum Distillation: Performed for compounds with high boiling points (>150°C) or those that decompose at their normal boiling point. Lowering the pressure reduces the boiling point of the substance, allowing distillation at a lower, safer temperature.

Adsorption of Gases:

Gases with lower critical temperatures are less easily liquefied and therefore show less adsorption on adsorbents (e.g., charcoal). Hydrogen (H2) has the lowest critical temperature among common gases like CO2, SO2, CH4, H2, hence it shows the least adsorption.

Gas Permeation in Plastics:

The rate of permeation of gases through plastics depends on: Type of plastics (material prop1. erties). Thickness of plastics (diffusion 2. path length). Concentration of gas (driving 3. force, partial pressure difference). Temperature of gas (affects mo4. lecular kinetic energy and polymer matrix properties).

Types of Solutions (e.g., Solid in Liquid, Liquid in Liquid, Gas in Liquid)

Solution Types (Solute-Solvent):

Gas in Liquid: Carbonated drinks (CO2 in water, e.g., Coca-Cola), Oxygen in water.
Solid in Liquid: Brine (salt in water), sugar in water.
Liquid in Liquid: Vinegar (acetic acid in water), alcohol in water.
Solid in Solid: Alloys (e.g., Brass, Bronze).

Separation Techniques for Homogeneous Mixtures:

Distillation: Separates miscible liquids or a non-volatile solid from a volatile liquid, based on boiling point differences.
Simple Distillation: For miscible liquids with significant boiling point difference (e.g., >25°C).
Fractional Distillation: For miscible liquids with close boiling points (e.g., acetone and methyl alcohol), or complex mixtures like petroleum.
Applications of Fractional Distillation: Refining of petroleum, separation of ethanol from water.
Hickman Head: Apparatus for microdistillation, typically used for volumes less than 1 mL.

Azeotropic Mixture: A constant boiling mixture that distils without changing its composition.

Example: Ethanol (approx. 95.6%) and water (approx. 4.4%) by weight.

Permanent Hardness of Water Removal Methods:

Ion-exchange method (e.g., Zeolite/ Permutit process, synthetic resins).
Washing soda treatment.
Note: Boiling and lime treatment remove temporary hardness.

3. Inorganic Chemistry

Practice MCQs: Physical and Chemical Changes, Solution

Concept of Solutions: Solute, Solvent, and Components

Tincture of iodine is:
Asked in: UPSC Geoscientist 2021
1. a solution of iodine in alcohol only.
2. a solution of iodine in water only.
3. a solution of iodine in alcohol and water.
4. iodine.
Show answer
Answer: C. a solution of iodine in alcohol and water.
Quantum numbers: - Principal quantum number ($n$): Shell (1, 2, 3, ...) - Azimuthal quantum number ($l$): Subshell (s, p, d, f for $l=0, 1, 2, 3$ respectively) - Magnetic quantum number ($m_l$): Orbital orientation ($ -l, ..., 0, ..., +l $) - Spin quantum number ($m_s$): Electron spin ($ +1/2 $ or $ -1/2 $) The orbital notation is given by $n$ followed by the subshell letter (e.g., 1s, 2p, 3d).
Group of orbitals having identical values of (n + 1) is - - (5) Question not attempted
Asked in: Department Recruitment 2024 (Chemist) 2024
1. 3d, 3p, 4s
2. 3d, 4p, 5s
3. 4s, 3d, 5p
4. 3p, 3d, 4f
Show answer
Answer: B. 3d, 4p, 5s
The $(n+l)$ rule is a general guideline for determining the order of energy levels of atomic orbitals. Orbitals with a lower sum of the principal quantum number ($n$) and the azimuthal quantum number ($l$) are filled first. If two orbitals have the same $ (n+l)$ value, the orbital with the lower $n$ value has lower energy. In this question, we are looking for orbitals with identical $(n+l)$ values. - For 3d: $n=3, l=2$, $n+l=5$. - For 4p: $n=4, l=1$, $n+l=5$. - For 5s: $n=5, l=0$, $n+l=5$. All three orbitals have an $(n+l)$ value of 5. Tincture of iodine is a solution of iodine, commonly dissolved in a mixture of alcohol (ethanol) and water.
32 g of methane (molar mass 16 g/mol) is mixed with 192 g of oxygen (molar mass 32 g/ mol). Presuming that these gases donot react with each other, what is the mole fraction of methane ?
Asked in: MPSC CS Prelims 2021
1. 0.25
2. 6
3. 0.167
4. 4
Show answer
Answer: A. 0.25
Mole fraction is defined as the number of moles of a component divided by the total number of moles of all components in the mixture. First, calculate the number of moles of methane (CH₄) and oxygen (O₂): Number of moles of CH₄ = Mass / Molar Mass = 32 g / 16 g/mol = 2 moles. Number of moles of O₂ = Mass / Molar Mass = 192 g / 32 g/ mol = 6 moles. Total number of moles = Moles of CH₄ + Moles of O₂ = 2 moles + 6 moles = 8 moles.
The maximum number of molecules are present in _______. [H = 1, C = 12, O = 16, I = 127]
Asked in: MPSC CS Prelims 2022
1. 250 g of iodine crystals
2. 22 g of carbon dioxide
3. 45 g of water
4. 10 g of hydrogen gas
Show answer
Answer: D. 10 g of hydrogen gas
- The number of molecules is proportional to the number of moles. - Number of moles is calculated by dividing the mass by the molar mass. - Molar mass is the sum of atomic masses of all atoms in a molecule.
180 g of acetic acid (CH₃COOH) is mixed with 180 g of water (H₂O). The mole fraction of acetic acid in the resultant solution is [H = 1, C = 12, O = 16]
Asked in: MPSC CS Prelims 2023
1. 0.23
2. 1.0
3. 0.5
4. None of the above
Show answer
Answer: A. 0.23
Mole fraction is a unitless quantity defined as the ratio of the number of moles of a component to the total number of moles in a mixture.
Which one of the following solutions is not capable of conducting electricity?
Asked in: UPSC NDA 2 2022
1. Copper sulphate
2. Sodium chloride
3. Sugar
4. Sodium hydroxide
Show answer
Answer: C. Sugar
For a solution to conduct electricity, it must contain free-moving ions. Solutions of ionic compounds (like Copper sulphate, Sodium chloride, Sodium hydroxide) dissociate into ions when dissolved in water, allowing them to conduct electricity. Sugar (sucrose) is a covalent compound; when it dissolves in water, it remains as neutral molecules and does not produce ions.
The aqueous solution of potassium chloride is
Asked in: TNPSC CS Prelims 2017
1. a weak electrolyte
2. a strong electrolyte
3. a non-electrolyte
4. initially weak and then become a strong elec‐ trolyte
Show answer
Answer: B. a strong electrolyte
An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. Strong electrolytes dissociate completely or nearly completely into ions when dissolved in water, whereas weak electrolytes only partially dissociate. Non-electrolytes do not dissociate into ions in solution.
Given below are two statements, one is labelled as Assertion (A) and the other as Reason (R). Assertion (A): A solution of table salt in a glass of water is homogeneous. Reason (R): A solution having different composition throughout is homogeneous. Select the correct answer from the code given below:
Asked in: UPPCS Prelims 2022
1. (A) is false but (R) is true
2. (A) is true but (R) is false
3. Both (A) and (R) are true but (R) is not the correct explanation of (A)
4. Both (A) and (R) are true and (R) is the correct explanation of (A)
Show answer
Answer: B. (A) is true but (R) is false
A homogeneous solution has a uniform composition throughout, while a heterogeneous mixture has a non-uniform composition.
Water is a good solvent for dissolving ionic compounds because
Asked in: UPSC CAPF 2024
1. It has a high specific heat
2. It has no colour
3. It has a high dipole moment
4. It has a high boiling point
Show answer
Answer: C. It has a high dipole moment
Water's ability to dissolve ionic compounds stems primarily from its strong polarity and high dipole moment, which allows it to hydrate (surround and separate) the positive and negative ions.

Definition and Characteristics of Chemical Changes (Chemical Reactions)

Which of the following slows down the reaction rate?
Asked in: BPSC Prelims Exam 69th
1. Catalytic promoter
2. Homogeneous catalyst
3. Heterogeneous catalyst
4. None of the above
Show answer
Answer: D. None of the above
- Catalysts accelerate reaction rates. - Promoters enhance catalyst activity. - Inhibitors slow down reaction rates.
Which one of the following is an example of chemical change ?
Asked in: UPSC CDS 1 2016 · UPSC NDA 1 2022
1. Burning of paper
2. Magnetization of soft iron
3. Dissolution of cane sugar in water
4. Preparation of ice cubes from water
Show answer
Answer: A. Burning of paper
- A chemical change involves a chemical reaction where one or more substances are transformed into different substances with different properties. - Burning is a combustion reaction where paper reacts with oxygen, producing ash, carbon dioxide, water vapor, and other substances. This process forms new chemical compounds and is not easily reversible. - Physical changes alter the form or appearance of a substance but not its chemical composition. Magnetization, dissolution, and phase changes (like freezing water) are physical changes, as the original substances retain their chemical identity and the process is often reversible.
The number of moles of oxygen gas used in the complete combustion of 1 mole of glucose is :
Asked in: UPSC CDS 1 2022
1. 1
2. 3
3. 6
4. 12
Show answer
Answer: C. 6
Complete combustion of a hydrocarbon or carbohydrate involves reaction with sufficient oxygen to produce carbon dioxide (CO2) and water (H2O). Balancing the chemical equation ensures that the number of atoms of each element is the same on both the reactant and product sides, representing the stoichiometric ratios.
Which one of the following is not an example of an oxidation reaction ?
Asked in: UPSC CDS 1 2022 · UPSC CDS 1 2023
1. The taste of butter changes if left for a longer period
2. A white substance is formed when an aqueous solution of barium chloride is mixed with sodium sulphate solution
3. A reddish-brown powder gets coated on articles made of iron
4. Wine gets sour with time
Show answer
Answer: B. A white substance is formed when an aqueous solution of barium chloride is mixed with sodium sulphate solution
Oxidation is a chemical process involving the loss of electrons, gain of oxygen, or loss of hydrogen. Redox reactions involve both oxidation and reduction. Precipitation reactions, where insoluble salts form from the mixing of solutions, are generally non-redox reactions if the oxidation states of the ions remain unchanged.
Consider the following statements regarding burning of magnesium ribbon in air : 1. White powder of MgO is formed. 2. It is an example of combustion reaction. 3. Heat and light are produced. Which of the statements given above are correct?
Asked in: UPSC CDS 1 2023
1. 1 and 2 only
2. 1 and 3 only
3. 2 and 3 only
4. 1, 2 and 3
Show answer
Answer: D. 1, 2 and 3
Burning of magnesium is a combustion reaction producing magnesium oxide, heat, and light.
Which among the following methods is used to separate the constituents present in a compound ?
Asked in: UPSC CDS 2 2023
1. Electrochemical method
2. Heating method
3. Fractional distillation
4. Decomposition followed by ion exchange
Show answer
Answer: A. Electrochemical method
Separating constituents of a compound involves breaking chemical bonds, which is a chemical process (decomposition). This is distinct from separating components of a mixture, which involves physical methods like distillation, filtration, etc.
When 10 g of calcium carbonate is decomposed completely, then 5.6 g of calcium oxide is formed along with the generation of carbon dioxide. Mass of the carbon dioxide formed is:
Asked in: UPSC Geoscientist 2020
1. 4.4 g
2. 5.6 g
3. 4.6 g
4. 4.8 g
Show answer
Answer: A. 4.4 g
According to the Law of Conservation of Mass, the total mass of the reactants in a chemical reaction is equal to the total mass of the products. In this decomposition reaction, Calcium Carbonate (CaCO₃) decomposes into Calcium Oxide (CaO) and Carbon Dioxide (CO₂).
Consider the following statements about the hardness of water :
Asked in: KPSC KAS Prelims 2015
1. Temporary hardness is caused by the presence of dissolved calcium bicarbonate and magnesium bicarbonate.
2. Permanent hardness is caused by the presence of dissolved calcium sulphate/ calcium chloride and/or magnesium sulphate/magnesium chloride.
3. One of the methods of removing per‐ manent hardness is boiling the hard wa‐ ter. Which of the above statements is/are correct ? Select the code for the correct answer from the options given below : A. A only B. A and B only C. B and C only
4. A, B and C
Show answer
Answer: B. Permanent hardness is caused by the presence of dissolved calcium sulphate/ calcium chloride and/or magnesium sulphate/magnesium chloride.
Hardness of water is due to the presence of dissolved metal ions, primarily Ca²⁺ and Mg²⁺. Temporary hardness can be removed by boiling, while permanent hardness requires other methods like ion exchange or chemical precipitation.
What are the metallic constituents of hard water ?
Asked in: KPSC KAS Prelims 2017
1. Magnesium, Calcium and Tin
2. Iron, Tin and Calcium
3. Calcium, Magnesium and Iron
4. Magnesium, Tin and Iron
Show answer
Answer: C. Calcium, Magnesium and Iron
Hard water is water that has a high mineral content, specifically high concentrations of dissolved divalent metallic cations. The primary ions responsible for hardness are Calcium (Ca²⁺) and Magnesium (Mg²⁺). While other metallic ions like Iron (Fe²⁺ or Fe³⁺) and Manganese (Mn²⁺) can also contribute, Calcium and Magnesium are the most prevalent contributors to both temporary and permanent hardness. Tin is not a typical metallic constituent causing water hardness.

Definition and Characteristics of Physical Changes

A mixture of sand and naphthalene can be separated by
Asked in: BPSC Prelims Exam 66th
1. sublimation
2. distillation
3. chromatography
4. fractional distillation
Show answer
Answer: A. sublimation
Sublimation is the process where a substance transitions directly from the solid phase to the gas phase without passing through the liquid phase. Naphthalene is a substance that sublimes readily at relatively low temperatures. Sand (primarily silicon dioxide) does not sublime under typical conditions. To separate the mixture, one can heat it gently; the naphthalene will vaporize and can be collected by condensing the vapor on a cool surface, leaving the sand behind.
Which one of the following is a physical change?
Asked in: UPSC CDS 1 2017 · UPSC Geoscientist 2022
1. Burning of coal
2. Burning of wood
3. Heating of a platinum crucible
4. Heating of potassium chlorate
Show answer
Answer: C. Heating of a platinum crucible
A physical change is a change in the form of a substance, but not in its chemical identity. Chemical changes involve a chemical reaction where new substances are formed. - Burning of coal and wood are combustion reactions where the substance reacts with oxygen to form ash, carbon dioxide, etc. These are chemical changes. - Heating of potassium chlorate (KClO₃) typically refers to its thermal decomposition, which produces potassium chloride (KCl) and oxygen (O₂). This is a chemical change. - Heating a platinum crucible: Platinum is a very noble (unreactive) metal. Heating it, even to high temperatures in air, usually only changes its temperature or potentially causes thermal expansion or changes in its physical state (if heated to melting point). It does not readily undergo a chemical reaction or decomposition under normal heating conditions in a lab. Therefore, heating a platinum crucible is primarily a physical change.
Employing Chromatography, one cannot separate
Asked in: UPSC CDS 2 2019
1. radio-isotopes
2. colours from a dye
3. pigments from a natural colour
4. drugs from blood
Show answer
Answer: A. radio-isotopes
Radio-isotopes are different forms of the same element, differing only in the number of neutrons (and thus mass) but having the same chemical properties. Chromatography separates based primarily on physical or chemical interactions that relate to solubility, adsorption, volatility, size, or charge. Since isotopes of an element have virtually identical chemical behaviour, chromatography is generally not a suitable method for separating radio-isotopes. Techniques like mass spectrometry, gas diffusion, or centrifugation are typically used for isotope separation based on mass differences.
At a given temperature and pressure, the force of attraction among the molecules will be highest in case of:
Asked in: UPSC Geoscientist 2020
1. helium
2. sugar
3. water
4. carbon tetrachloride
Show answer
Answer: B. sugar
The state of matter (solid, liquid, gas) reflects the strength of intermolecular forces. Solids have the strongest forces, liquids have intermediate forces, and gases have the weakest forces. Sugar is a solid at room temperature and pressure, while the other substances are liquids or gases.
Which one of the following statements is correct about camphor and ammonium chloride?
Asked in: UPSC Geoscientist 2020
1. Both of them are inorganic compounds
2. Both of them are organic compounds
3. Both of them undergo sublimation
4. Camphor is an element but ammonium chloride is a compound
Show answer
Answer: C. Both of them undergo sublimation
Sublimation is the process where a substance transitions directly from the solid to the gas state, without passing through the liquid state. Both camphor and ammonium chloride exhibit this property under appropriate conditions.
Number of states of matter known so far is:
Asked in: UPSC Geoscientist 2020
1. 3
2. 4
3. 5
4. 6
Show answer
Answer: C. 5
The three classical states of matter are Solid, Liquid, and Gas. Beyond these, Plasma is widely recognized as a fourth state, and the Bose-Einstein Condensate (BEC) is considered a fifth state.
नीचे अवस्था पǐरिवर्तन के कु छ प्रकारि Ǒदिए गए हैं : A. जल का वाष्पीकरिण B. मोमबत्ती का जलना C. जल में चीनी का घुलना D. जल के वैद्यु अपघटन द्वारिा हाइड्रोजन औरि ऑक्सीजन को बनाना सही ͪवकल्प को चुǓनए :
Asked in: HAS Prelims 2021
1. B, C तथा D में के वल रासायlनिक पåरवतर्तनि सlÌमlलत है।
2. A, B तथा C में के वल भौlतक पåरवतर्तनि सlÌमlलत है।
3. के वल A एक भौlतक पåरवतर्तनि है।
4. B में भौlतक और रासायlनिक, दोनिों पåरवतर्तनि होते हैं।
Show answer
Answer: D. B में भौlतक और रासायlनिक, दोनिों पåरवतर्तनि होते हैं।
भौlतक पåरवतर्तनि में पदाथर्त की रासायlनिक पहचानि बदले lबनिा उसके भौlतक गुणों (जैसे अवस्था, आकार) में पåरवतर्तनि होता है। रासायlनिक पåरवतर्तनि में पदाथर्त की रासायlनिक संरचनिा बदल जाती है और निए पदाथर्त बनिते हैं।
Following are some processes involving changes of state : A. Evaporation of water B. Burning of candle C. Dissolution of sugar in water D. Electrolysis of water to form hydrogen and oxygen Select the correct option :
Asked in: HAS Prelims 2021
1. B, C and D involve chemical change only
2. A, B and C involve physical change only
3. Only A is a physical change
4. B involves both physical and chemical change
Show answer
Answer: D. B involves both physical and chemical change
Physical changes alter the form or appearance of a substance but not its chemical composition. Chemical changes result in the formation of new substances with different chemical properties.
Consider the following statements: 1. Evaporation is a surface phenomenon, meaning particles from the surface change into vapour state. 2. Boiling is a bulk phenomenon, meaning particles from the bulk of the liquid change into vapour state. 3. Deposition is the change of gaseous state directly to solid state without changing into liquid state. 4. The state of matter can only be changed by changing its temperature. Which of the following is correct?
Asked in: HAS Prelims 2021
1. 1, 3 and 4
2. 1, 2 and 3
3. 1, 2 and 4
4. 2, 3 and 4
Show answer
Answer: B. 1, 2 and 3
Phase changes (solid, liquid, gas) are influenced by both temperature and pressure. Evaporation is a surface phenomenon, while boiling is a bulk phenomenon. Deposition is the phase transition from gas to solid.

Distinction between Physical and Chemical Changes

Consider the following statements about mixture : A substance can be separated into other kinds of matter by any physical process. Dissolved sodium chloride can be separated from water by the physical process of evaporation. Which of the statements given above is/are correct ?
Asked in: UPSC CDS 2 2019
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Show answer
Answer: B. 2 only
Physical processes are used to separate components of mixtures based on their physical properties. Chemical processes are required to break down compounds into simpler substances.
In which one of the following cases do both physical and chemical changes take place?
Asked in: UPSC CDS 2 2023
1. Burning of candle
2. Freezing of water
3. Cooking of food
4. Rusting of iron
Show answer
Answer: A. Burning of candle
In the burning of a candle, the wax melts (physical change) and turns into liquid. This liquid wax is then drawn up the wick, vaporizes, and reacts with oxygen in the air (combustion), producing carbon dioxide, water vapor, heat, and light (chemical change). Thus, both physical (melting/vaporization of wax) and chemical (combustion of wax vapor) changes occur simultaneously as the candle burns.
Match List - I with List - II: List - I List - II 1. Solid Sodium Chloride with I. Chromato‐ Camphor graphy 2. Various pigments from ex‐ II. Distillation tract of flower petals 3. Mixture of Acetone and Wa‐ III. Centrifuter gation IV. Sublima‐ 4. Butter from Cream tion
Asked in: HAS Prelims 2021
1. 1-II, 2-I, 3-IV, 4-III
2. 1-II, 2-III, 3-IV, 4-I
3. 1-IV, 2-I, 3-II, 4-III
4. 1-IV, 2-III, 3-I, 4-II
Show answer
Answer: C. 1-IV, 2-I, 3-II, 4-III
Different separation techniques exploit different physical or chemical properties of the components in a mixture, such as boiling point (distillation), volatility (sublimation), differential adsorption/ solubility (chromatography), and density (centrifugation).
Indicate which of the following is a pure substance ? (a) Iron (b) Gasoline (c) Cow's milk (d) Sea Water
Asked in: MPSC CS Prelims 2013
1. (b), (c) and (d)
2. (a) only
3. (b) only
4. (c) only
Show answer
Answer: B. (a) only
A pure substance is a substance that consists of only one type of particle, which can be atoms or molecules. Pure substances are either elements or compounds. Mixtures are composed of two or more different substances that are not chemically bonded together. (a) Iron (Fe) is an element, which is a pure substance. (b) Gasoline is a complex mixture of various hydrocarbons. (c) Cow's milk is a mixture of water, fats, proteins, lactose, minerals, etc. (d) Sea water is a solution (a type of mixture) of various salts dissolved in water. Therefore, only Iron is a pure substance among the given options.
What is not a mixture?
Asked in: MPSC CS Prelims 2014
1. Water
2. Air
3. Soil
4. Chalk
Show answer
Answer: A. Water
A mixture consists of substances physically combined, not chemically bonded. Pure water (H₂O) is a chemical compound.
Which one of the following is not a chemical change?
Asked in: UPSC NDA 1 2016
1. Ripening of fruits
2. Curdling of milk
3. Freezing of water
4. Digestion of food
Show answer
Answer: C. Freezing of water
Chemical changes result in new substances; physical changes do not change the chemical composition.
Which one of the following substances is NOT a mixture ?
Asked in: UPSC NDA 1 2019
1. Ice
2. Ice-cream
3. Air
4. Honey
Show answer
Answer: A. Ice
A mixture is a substance comprising two or more components that are not chemically bonded. Ice is the solid state of water (H₂O). Water is a chemical compound, meaning it is formed from different elements (Hydrogen and Oxygen) chemically combined in a fixed ratio. A compound is considered a pure substance. Ice-cream is a mixture of water, milk solids, sugars, fats, flavorings, and air. Air is a mixture of gases, primarily nitrogen, oxygen, argon, and carbon dioxide. Honey is a mixture consisting mainly of sugars and water, along with other components like enzymes, minerals, etc.
Match List I with List II and select the correct answer using the code given below the Lists : List II List I (Type of (Process) change)
Asked in: UPSC NDA 2 2016
1. Heating Camphor 1. Chemical
2. Cooling of water vapour up to 2. Evapora‐ room temperature tion 3. Condensa‐
3. Cooking an egg tion
4. Formation of water vapour at 4. Sublima‐ room temperature tion Code : A. A-4, B-3, C-1, D-2 B. A-4, B-1, C-3, D-2 C. A-2, B-1, C-3, D-4 D. A-2, B-3, C-1, D-4
Show answer
Answer: A. Heating Camphor 1. Chemical
- Physical changes alter the form or appearance of a substance but not its chemical composition (e.g., melting, boiling, freezing, condensation, sublimation, dissolution). - Chemical changes result in the formation of new substances with different chemical properties (e.g., cooking, burning, rusting, digestion).
Consider the following statements in view of rusting of Iron :
Asked in: TSPSC Group 1 Prelims 2022
1. It is chemically named as Iron Oxide.
2. Rusting is considered as a chemical change.
3. Zinc is coated on iron articles to prevent them from rusting. Choose the correct answer : A. A & B only B. B & C only C. A & C only
4. A, B and C
Show answer
Answer: D. A, B and C
Rusting is an oxidation reaction of iron. It is a chemical change. Galvanization uses zinc coating to prevent iron from rusting.

Distinguishing Solutions, Colloids, and Suspensions

Very small insoluble particles in a liquid may be separated from it by using
Asked in: UPSC CDS 1 2019
1. crystallization
2. fractional distillation
3. centrifugation
4. decantation
Show answer
Answer: C. centrifugation
- Centrifugation uses centrifugal force to separate solids from liquids based on density. - It is effective for separating very small or finely suspended insoluble particles.
An emulsion consists of
Asked in: UPSC CDS 2 2017
1. one liquid and one solid
2. one liquid and one gas
3. two liquids
4. two solids
Show answer
Answer: C. two liquids
In an emulsion, one liquid is dispersed in the other in the form of tiny droplets.
In which of the following colloids is the dispersing medium a liquid ?
Asked in: UPSC CDS 2 2024
1. Mist
2. Foam
3. Jelly
4. Shaving cream
Show answer
Answer: C. Jelly
- Colloids are mixtures with particles intermediate in size between solutions and suspensions. - Identifying the dispersed phase and dispersing medium is key to classifying colloids.
In which of the following conditions distance between molecules of carbon dioxide filled in a container may increase? (i) On increasing the volume of container (ii) On leakage of some carbon dioxide gas from the container (iii) On increasing air pressure in the container (iv) On adding more carbon dioxide gas in container without changing its size
Asked in: CGPSC Prelims Exam 2021
1. (ii) and (iii)
2. (iii) and (iv)
3. (i) and (iii)
4. (i) and (ii)
Show answer
Answer: D. (i) and (ii)
The distance between molecules of a gas in a container is related to the volume the gas occupies and the number of molecules. (i) On increasing the volume of the container while the amount of gas remains the same, the molecules have more space, increasing the average distance between them. (ii) On leakage of some gas, the number of molecules decreases while the volume remains the same, leading to an increase in the average distance between the remaining molecules. (iii) Increasing air pressure in the container (assuming by adding air, not compressing the CO2) in a fixed volume increases the total number of molecules, thus decreasing the average distance between all molecules, including CO2. If interpreted as compressing the CO2, the volume decreases, decreasing distance. (iv) Adding more CO2 gas to a container of fixed size increases the number of molecules in the same volume, decreasing the average distance. Therefore, only conditions (i) and (ii) would increase the distance between CO2 molecules.
Which one of the following is NOT an example of colloids?
Asked in: UPSC Geoscientist 2020
1. Milk
2. Jelly
3. Tincture of iodine
4. Fog
Show answer
Answer: C. Tincture of iodine
A colloid is a heterogeneous mixture where the solute particles are dispersed uniformly throughout the solvent. The particle size in colloids is typically between 1 nm and 1000 nm. True solutions have particle sizes smaller than 1 nm.
The dye in black ink can be separated by the method of:
Asked in: UPSC Geoscientist 2020
1. evaporation
2. fractional distillation
3. dialysis
4. chromatography
Show answer
Answer: D. chromatography
Black ink is typically a mixture of several different coloured dyes. Chromatography is a technique used to separate components of a mixture based on their differential partitioning between a stationary phase and a mobile phase. Different dyes in the ink travel at different rates through the stationary phase (like paper), causing them to separate.
Which one of the following mixtures will not have uniform composition?
Asked in: UPSC Geoscientist 2022
1. Oil in water
2. Sulphur in carbon disulphide
3. Alcohol in water
4. Sugar in water
Show answer
Answer: A. Oil in water
A mixture with uniform composition throughout is called a homogeneous mixture, while a mixture with non-uniform composition is called a heterogeneous mixture. Solutions (like sugar in water, alcohol in water, sulphur in carbon disulphide) are homogeneous mixtures.
If balloon is filled with dry air which contains mixture of 79% N2 and 21% O2 at 25°C then which component of the air will effuse out first ? (a) O2, because it has higher mass than N2 (b) N2, because it has lower mass than O2 (c) O2 and N2 both will effuse out at the same time (d) Whole air will effuse out and balloon will regain its original shape
Asked in: MPSC CS Prelims 2013
1. (a) and (b)
2. (c) and (d)
3. (a) only
4. (b) only
Show answer
Answer: D. (b) only
According to Graham's Law of Effusion, the rate of effusion of a gas is inversely proportional to the square root of its molar mass. Given the same temperature and pressure, lighter gases effuse faster than heavier gases. The molar mass of N₂ is approximately 28 g/mol, and the molar mass of O₂ is approximately 32 g/mol. Since N₂ has a lower molar mass than O₂, it will effuse out of the balloon faster than O₂.
Glass is a
Asked in: UPSC NDA 1 2017
1. liquid
2. colloid
3. non-crystalline amorphous solid
4. crystalline solid
Show answer
Answer: C. non-crystalline amorphous solid
Glass lacks the long-range crystalline order found in crystalline solids and is considered an amorphous solid.

Energy Changes in Chemical Reactions (Exothermic and Endothermic Processes)

For a certain reaction, $\Delta G^0 = -45$ kJ/mol and $\Delta H^0 = -90$ kJ/mol at 0 °C. What is the minimum temperature at which the reaction will become spontaneous, assuming that $\Delta H^0$ and $\Delta S^0$ are independent of temperature?
Asked in: UPSC CDS 1 2019
1. 273 K
2. 298 K
3. 546 K
4. 596 K
Show answer
Answer: C. 546 K
- Spontaneity requires $\Delta G
The EMF of a chemical cell is positive, when the free energy change of the reaction is _______ .
Asked in: MPSC CS Prelims 2020
1. > 0
2. < 0
3. = 0
4. No relationship between the free energy change and EMF
Show answer
Answer: B. < 0
- The relationship is $\Delta G = -nFE$. - A positive EMF ($E > 0$) indicates a spontaneous reaction. - A spontaneous reaction is associated with a negative change in free energy ($\Delta G
Which one of the following energy is stored in the links between the atoms ?
Asked in: UPSC NDA 1 2019
1. Nuclear energy
2. Chemical energy
3. Potential energy
4. Thermal energy
Show answer
Answer: B. Chemical energy
Chemical energy is the potential energy stored within the chemical bonds between atoms in molecules. When chemical reactions occur, these bonds are broken and new bonds are formed, releasing or absorbing energy. Nuclear energy is stored within the nucleus of an atom, in the forces holding protons and neutrons together. Potential energy is stored energy based on position or state (e.g., gravitational potential energy, elastic potential energy). Thermal energy is energy associated with the temperature of an object due to the kinetic energy of its atoms and molecules.
Reaction of quick lime (CaO) with water to produce slaked lime (Ca(OH)₂) is an example of
Asked in: UPSC NDA 1 2021
1. Displacement reaction.
2. Endothermic reaction.
3. Decomposition reaction.
4. Exothermic reaction.
Show answer
Answer: D. Exothermic reaction.
Exothermic reactions are chemical reactions that release energy, typically in the form of heat or light. Endothermic reactions absorb energy. Displacement reactions involve one element displacing another from a compound. Decomposition reactions involve a single compound breaking down into simpler substances. The reaction of quick lime with water fits the definition of an exothermic reaction due to the large heat release, also sometimes classified as a combination reaction.
Which one of the following is an example of endothermic reaction?
Asked in: UPSC CAPF 2021
1. CaO(s) + H₂O(l) → Ca(OH)₂(aq)
2. CaCO₃(s) → CaO(s) + CO₂(g)
3. C(s) + O₂(g) → CO₂(g)
4. CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)
Show answer
Answer: B. CaCO₃(s) → CaO(s) + CO₂(g)
An endothermic reaction is a reaction that absorbs heat from its surroundings. A) CaO(s) + H₂O(l) → Ca(OH)₂(aq) (Slaking of lime) is a highly exothermic reaction, releasing significant heat. B) CaCO₃(s) → CaO(s) + CO₂(g) (Decomposition of calcium carbonate) requires heating to occur, meaning it absorbs heat from the surroundings, making it an endothermic reaction. C) C(s) + O₂(g) → CO₂(g) (Combustion of carbon) is an exothermic reaction, releasing heat and light. D) CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) (Combustion of methane) is an exothermic reaction, releasing a large amount of heat.
Which one among the following is an example of endothermic process ?
Asked in: UPSC CAPF 2024
1. Combustion of carbon
2. Mixing acid and alkali
3. Photosynthesis
4. Respiration
Show answer
Answer: C. Photosynthesis
- An endothermic process absorbs heat or energy from the surroundings. The temperature of the surroundings typically decreases. - An exothermic process releases heat or energy into the surroundings. The temperature of the surroundings typically increases. - Photosynthesis converts light energy into chemical energy stored in glucose: $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Light Energy} \rightarrow \text{C}_6\text{H} _{12}\text{O}_6 + 6\text{O}_2$.
A reaction is spontaneous when
Asked in: WBPSC CS Prelims 2017
1. ∆G = - ve
2. ∆H = - ve
3. ∆S = + ve
4. ∆S = - ve
Show answer
Answer: A. ∆G = - ve
The spontaneity of a chemical reaction or physical process is primarily determined by the change in Gibbs Free Energy (∆G). The relationship is defined by the equation: ∆G = ∆H - T∆S, where ∆H is the change in enthalpy, T is the absolute temperature, and ∆S is the change in entropy. - If ∆G 0, the process is non-spontaneous under constant temperature and pressure (the reverse process is spontaneous). - If ∆G = 0, the system is at equilibrium.
Mg (s) + O₂ (g) → MgO (s) + energy, this reaction may be classified as a/an
Asked in: WBPSC CS Prelims 2023
1. Combination reaction
2. Oxidation reaction
3. Exothermic reaction
4. All of the above
Show answer
Answer: D. All of the above
Combination Reaction Two or more reactants (Mg and O₂) combine to form a single product (MgO). This fits the definition of a combination reaction. 2. Oxidation Reaction Magnesium (Mg) reacts with Oxygen (O₂). In this reaction, Mg loses electrons (its oxidation state changes from 0 to +2) and is oxidized. The reaction with oxygen is a classic example involving oxidation. 3. Exothermic Reaction The term "+ energy" on the product side indicates that energy is released during the reaction. Reactions that release energy are classified as exothermic reactions.Since the reaction fits the description of a Combination reaction, an Oxidation reaction, and an Exothermic reaction, all the individual classifications listed are correct. 189. Which of the following are exothermic processes ? Choose the correct option : - Reaction of water with quick lime - Dilution of sulphuric acid - Evaporation of water - Sublimation of camphor (crystals) - Question not attempted
Asked in: Deputy Jailor 2024
1. (i) and (ii)
2. (ii) and (iii)
3. (i) and (iv)
4. (iii) and (iv)
Show answer
Answer: A. (i) and (ii)
Exothermic processes release energy, typically as heat, while endothermic processes absorb energy. The reaction of water with quicklime and the dilution of sulphuric acid are well-known exothermic reactions.

Methods of Expressing Concentration of Solutions (Mass Percentage, Volume Percentage, Molarity, Molality, Parts Per Million)

The amount of solute present per unit volume or per unit mass of the solution/solvent is known as ______ in Chemistry.
Asked in: BPSC Prelims Exam 69th
1. composition of solute
2. concentration of solvent
3. concentration of solute
4. concentration of solution
Show answer
Answer: D. concentration of solution
Concentration is a measure of how much solute is dissolved in a given amount of solvent or solution.
A solution contains 20 g of solute in 180 g of solvent. If the solvent is water, what is the concentration of the solution in terms of mass percentage ?
Asked in: UPSC CDS 1 2021
1. 11·1%
2. 22·2%
3. 10%
4. 20%
Show answer
Answer: C. 10%
- Mass of solute = 20 g - Mass of solvent = 180 g - Mass of solution = Mass of solute + Mass of solvent = 20 g + 180 g = 200 g - Mass percentage = (20 g / 200 g) × 100% = (1/10) × 100% = 10%.
There are two vessels V1 and V2, both containing Benzene solution of 40% concentration. Meena added some pure Benzene to V1 to bring the concentration to 50%. In the vessel V2, she took out some quantity of the solution and replaced it with an equal quantity of pure Benzene, to bring the concentration of it also to 50%. What is the ratio of the amount of Benzene added by Meena in V1 and V2, if the quantity of initial solutions in V1 and V2 are in the ratio of 1 : 2?
Asked in: GPSC Prelims CSP 1 2022
1. 8:3
2. 3:5
3. 1:5
4. 4:3
Show answer
Answer: B. 3:5
- In Vessel V1, pure Benzene is added. The initial quantity ratio is V1:V2 = 1:2. Let the initial quantity in V1 be x and in V2 be 2x. - Initial Benzene in V1 = 40% of x = 0.4x. Initial total solution = x. - Let 'a' be the amount of pure Benzene added to V1. New Benzene = 0.4x + a. New total solution = x + a. - New concentration in V1 = (0.4x + a) / (x + a) = 0.50. Solving for a: 0.4x + a = 0.5x + 0.5a => 0.5a = 0.1x => a = 0.2x. - In Vessel V2, some solution is taken out and replaced by an equal quantity of pure Benzene. Let 'q' be the quantity taken out and replaced. - Initial Benzene in V2 = 40% of 2x = 0.8x. Initial total solution = 2x. - When q is taken out, 0.4q of Benzene is removed. Benzene remaining = 0.8x - 0.4q. Solvent remaining = 1.2x - 0.6q. - q liters of pure Benzene are added. New Benzene = (0.8x - 0.4q) + q = 0.8x + 0.6q. New total solution = (2x - q) + q = 2x. - New concentration in V2 = (0.8x + 0.6q) / (2x) = 0.50. Solving for q: 0.8x + 0.6q = x => 0.6q = 0.2x => q added in V1 is a = 0.2x = (1/5)x. The amount of Benzene added in V2 is q = (1/3)x. - The ratio of Benzene added in V1 and V2 is a : q = (1/5)x : (1/3)x = 1/5 : 1/3. - Multiplying by the LCM of 5 and 3 (which is 15) gives the ratio 3 : 5.
How is 1.0N H₂SO₄ solution is prepared from 10 dm³ of 1.5M H₂SO₄ solution ?
Asked in: MPSC CS Prelims 2023
1. By adding 5 dm³ of water to it
2. By adding 294 g of H₂SO₄ to it
3. By adding 20 dm³ of water to it
4. By adding 174 g of H₂SO₄ to it
Show answer
Answer: C. By adding 20 dm³ of water to it
Normality is concentration expressed in equivalents per litre. It is useful in titration calculations. For acids, the equivalent weight is the molar mass divided by the number of acidic hydrogens (protons) that react. Dilution follows the principle that the amount of solute remains constant, so the initial normality times volume equals the final normality times volume (N₁V₁ = N₂V₂).
If one mole of an ideal gas occupies 22.4 Lit at Standard Temperature and Pressure, then the value of the universal gas constant R is
Asked in: MPSC CS Prelims 2023
1. 0.0821 atm Lit mol⁻¹ K⁻¹
2. 8.314 × 10⁷ Joules K⁻¹ mol⁻¹
3. 82.1 atm Lit mol⁻¹ K⁻¹
4. 8.314 erg K⁻¹ mol⁻¹
Show answer
Answer: A. 0.0821 atm Lit mol⁻¹ K⁻¹
The universal gas constant R relates the pressure, volume, temperature, and number of moles of an ideal gas. Its value depends on the units used for P, V, and T. The value 0.0821 L atm K⁻¹ mol⁻¹ is derived from the ideal gas law at standard condi‐
20 g of common salt is dissolved in 180 g of water. What is the mass percentage of the salt in the solution?
Asked in: UPSC NDA 1 2017
1. 5%
2. 9%
3. 10%
4. 15%
Show answer
Answer: C. 10%
The mass percentage of a solute in a solution is calculated as (Mass of solute / Mass of solution) 100%. In this case, the mass of the solute (common salt) is 20 g, and the mass of the solvent (water) is 180 g. The mass of the solution is the sum of the mass of the solute and the mass of the solvent: Mass of solution = 20 g + 180 g = 200 g. Mass percentage of salt = (20 g / 200 g) 100%.
For the Daniel cell E° = 1.10 V. The value of equilibrium constant (K) for the reaction Zn(s) + Cu2+ (aq) → Zn2+ (aq) + Cu(s)
Asked in: TNPSC CS Prelims 2015
1. 4.36×1039
2. 2.79×1041
3. 6.53×1035
4. 1.55×1037
Show answer
Answer: D. 1.55×1037
- The standard cell potential (E°) of an electrochemical cell is related to the equilibrium constant (K) of the cell reaction by the equation: E° = (RT/nF) ln(K), or E° = (2.303RT/nF) log₁₀(K). - At 298 K (25°C), the term (2.303RT/F) is approximately 0.0592 V. - The number of electrons transferred (n) in the balanced reaction needs to be determined.
The unit for equivalent conductivity is
Asked in: TNPSC CS Prelims 2019
1. ohm⁻¹cm⁻¹
2. ohm⁻¹cm⁻¹
3. ohm⁻¹cm²eq⁻¹
4. S cm⁻²eq⁻¹
Show answer
Answer: C. ohm⁻¹cm²eq⁻¹
Equivalent conductivity (Λ_eq) is defined as the conductivity (κ) divided by the equivalent concentration (C_eq). The standard unit of conductivity (κ) is Siemens per centimeter (S cm⁻¹) or ohm⁻¹ cm⁻¹.
For a cell reaction A(S) + 2B⁺ ⇌ A²⁺ + 2B the equilibrium constant is found to be 10¹². Then the E⁰cell value is
Asked in: TNPSC CS Prelims 2014
1. 0.354 V
2. 0.708 V
3. 0.0295 V
4. 0.177 V
Show answer
Answer: A. 0.354 V
- The relationship between E⁰cell and K at 298K is E⁰cell = (0.0591/n) log₁₀(K), where n is the number of electrons transferred in the balanced redox reaction. - The given reaction is A(S) + 2B⁺ ⇌ A²⁺ + 2B. - The equilibrium constant K = 10¹².

Properties of Colloids (Tyndall Effect, Brownian Motion)

The following are some of the properties of the colloidal sols: a. Tyndall effect b. Brownian motion c. Maxwell distribution d. van der Waals forces
Asked in: MPSC CS Prelims 2019
1. a, b and c
2. a and b
3. a and c
4. b and d
Show answer
Answer: B. a and b
Colloidal solutions exhibit characteristic properties that distinguish them from true solutions and suspensions. The Tyndall effect is the scattering of light as a light beam passes through a colloid, caused by the dispersion of light by the larger colloidal particles. Brownian motion is the random, erratic movement of colloidal particles resulting from collisions with molecules of the dispersion medium.
Which among the following is NOT true with respect to colloidal solution ?
Asked in: UPSC NDA 2 2023
1. Particles are uniformly distributed throughout the solution
2. Colloidal solution is homogenous in nature
3. They show Tyndal effect
4. They do not settle down when kept undis‐ turbed
Show answer
Answer: B. Colloidal solution is homogenous in nature
Colloidal solutions are fundamentally heterogeneous mixtures. Although they may appear homogeneous to the naked eye because the dispersed particles do not settle out, they are heterogeneous at the microscopic level.
Match the following: Type of Colloid Example
Asked in: PPSC CS Prelims 2013
1. Gel 1. Paint
2. Emulsion 2. Butter
3. Sol 3. Fog
4. Aerosol 4. Milk Choose the correct code: A B C D (a) 2 1 4 3 (b) 1 4 2 3 (c) 2 4 1 3 (d) 4 3 1 2 A. (a) 2 1 4 3 B. (b) 1 4 2 3 C. (c) 2 4 1 3 D. (d) 4 3 1 2
Show answer
Answer: C. Sol 3. Fog
Colloids are heterogeneous mixtures in which very fine particles of one substance are dispersed in a continuous medium of another substance. Colloids are classified based on the state of the dispersed phase and the dispersion medium. - Gel: Dispersed phase is solid, dispersion medium is liquid (e.g., butter, cheese, jelly). - Emulsion: Dispersed phase is liquid, dispersion medium is liquid (e.g., milk, mayonnaise). - Sol: Dispersed phase is solid, dispersion medium is liquid (e.g., paint, ink, blood). - Aerosol: Dispersed phase is solid or liquid, dispersion medium is gas (e.g., smoke (solid in gas), fog (liquid in gas)).
Which one of the following will NOT show Tyndall effect ?
Asked in: UPSC CAPF 2019
1. Chalk powder freshly mixed with water
2. Lime juice
3. Few drops of milk mixed with water
4. Starch solution
Show answer
Answer: B. Lime juice
- Tyndall effect is a phenomenon where light is scattered as it passes through a colloid or suspension. - This scattering makes the path of the light beam visible. - True solutions do not show the Tyndall effect because the dissolved particles are too small.
Consider the following Assertion (A) : Alum is applied to stop bleeding from cuts. Reason (R) : Blood is colloidal system containing negatively charged colloidal particles. The Aluminum ions of Alum have high coagulating power so that the blood gets coagulated Select the correct answer using from the code given below :
Asked in: UPPSC Upper Mains 2010
1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true, but (R) is not the correct explanation of (A).
3. (A) is true, but (R) is false.
4. (A) is false, but (R) is true.
Show answer
Answer: A. Both (A) and (R) are true and (R) is the correct explanation of (A).
Alum is indeed used to stop bleeding from cuts (Assertion A). This is because blood is a colloidal suspension with negatively charged particles. The aluminum ions (Al³⁺) in alum are highly effective coagulating agents for these negative particles (Reason R), causing the blood to clot and stop bleeding.
Which one of the following is most likely to exhibit Tyndall effect?
Asked in: WBCS Main Paper 4 2023
1. Sugar and water mixture
2. Potash alum and water mixture
3. Chalk powder and water mixture
4. Potassium permanganate and water mixture
Show answer
Answer: C. Chalk powder and water mixture
True solutions (like sugar and water, potash alum and water, potassium permanganate and water) have solute particles that are too small (molecular or ionic size) to scatter visible light significantly, and thus do not exhibit the Tyndall effect.
The migration of colloidal particles in an electric field is called - (1) Tyndall effect (2) Electrophoresis (3) Electro – osmosis (4) Electro – dialysis (5) Question not attempted
Asked in: Department Recruitment 2024 (Chemist) 2024
1. Option 1
2. Option 2
3. Option 3
4. Option 4
Show answer
Answer: B. Option 2
Electrophoresis is the movement of charged colloidal particles in an electric field. The direction of movement depends on the charge of the colloidal particles.
Which of the following colloids is known as a sol ?
Asked in: Food Safety Officer 2022
1. Cell fluid
2. Milk
3. Cheese
4. Cloud
Show answer
Answer: D. Cloud
A sol is generally defined as a colloidal dispersion of a solid in a liquid. However, in broader classifications of colloids, various types exist.
The scattering of light by colloidal particles is called :
Asked in: Co operative Supervisor & Environment Supervisor (Group C) Exam 2023
1. Brownian movement
2. Tyndall effect
3. Adsorption
4. Electrophoresis
Show answer
Answer: B. Tyndall effect
The Tyndall effect is a characteristic property of colloidal solutions and is used to distinguish them from true solutions. The size of colloidal particles (typically between 1 nm and 1000 nm) is sufficient to scatter light.

Saturated, Unsaturated, and Supersaturated Solutions

Which one of the following statements is correct?
Asked in: UPPCS Prelims 2002
1. The boiling point of an aqueous solution is higher than that of pure water
2. Addition of solutes to a solution causes an increase in its water potential
3. The vapour pressure of the water in a solution is lower than that of pure water
4. When a solution is separated from water by a semi permeable membrane, water movement can be prevented by applying pressure to the solution
Show answer
Answer: D. When a solution is separated from water by a semi permeable membrane, water movement can be prevented by applying pressure to the solution
This statement accurately describes the phenomenon of osmosis and the concept of osmotic pressure. Osmosis is the movement of water across a semipermeable membrane from a region of higher water potential (or lower solute concentration) to a region of lower water potential (or higher solute concentration). Applying pressure to the solution increases its water potential. The pressure required to prevent the net movement of water into the solution across the semipermeable membrane is defined as the osmotic pressure of the solution.

Solubility and Factors Affecting Solubility (Temperature, Pressure)

The gas, which comes out on opening a soda water bottle, is
Asked in: BPSC Prelims Exam 63rd
1. carbon dioxide
2. hydrogen
3. nitrogen
4. sulfur dioxide
Show answer
Answer: A. carbon dioxide
- Carbonated drinks contain dissolved carbon dioxide under pressure. - Opening the bottle releases the pressure, causing CO₂ to escape.
Consider the following statements : 1. Addition of salt to pure water increases the boiling point of water and decreases the freezing point of water. 2. When methyl alcohol is added to water, boiling point of water decreases. Which of the above statements is/are correct?
Asked in: BPSC Prelims Exam 67th Re Exam
1. 1 only
2. 2 only
3. Both 1 and 2
4. Salt and methyl alcohol are same in behaviour
Show answer
Answer: C. Both 1 and 2
Statement 1 describes the colligative properties of a solution: adding a non-volatile solute (like salt) to a solvent (water) increases the boiling point (boiling point elevation) and decreases the freezing point (freezing point depression) of the solution compared to the pure solvent. Statement 2 describes the effect of mixing two volatile liquids with different boiling points. Adding methyl alcohol (boiling point ~65°C) to water (boiling point 100°C) results in a solution whose boiling point is lower than that of pure water (it will be between the boiling points of the components, depending on composition, and specifically lower than pure water's 100°C).
Desalination of seawater is done by using reverse osmosis. The pressure applied to the solution is
Asked in: UPSC CDS 2 2017
1. larger than osmotic pressure
2. smaller than osmotic pressure
3. equal to osmotic pressure
4. equal to atmospheric pressure
Show answer
Answer: A. larger than osmotic pressure
Osmosis is the spontaneous movement of solvent molecules through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration. Osmotic pressure is the pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis, often used to express the concentration of the solution. Reverse osmosis is a process where a solvent is forced through a semipermeable membrane from a region of high solute concentration to a region of low solute concentration by applying a pressure greater than the osmotic pressure. This is the principle used in desalination to separate pure water from seawater.
A glass of (1) tap water, (2) distilled water and (3) sea water is cooled to its solidification. The order in which they will solidify first is
Asked in: OPSC CS Prelims 2022
1. tap water, distilled water, sea water
2. distilled water, sea water, tap water
3. sea water, tap water, distilled water
4. distilled water, tap water, sea water
Show answer
Answer: D. distilled water, tap water, sea water
The freezing point of a solvent is lowered by the presence of dissolved solutes. This phenomenon is known as freezing point depression, a colligative property dependent on the concentration of solute particles. Distilled water is the purest, having a freezing point closest to 0°C. Tap water contains dissolved minerals (impurities), lowering its freezing point slightly. Sea water contains a high concentration of dissolved salts, significantly lowering its freezing point (to below 0°C). When cooling the three, the one with the highest freezing point (distilled water) will solidify first, followed by tap water, and lastly sea water.
Which one among the following salts causes hardness to the water?
Asked in: UPSC CAPF 2012
1. Calcium bicarbonate
2. Calcium carbonate
3. Sodium sulphate
4. Potassium chloride
Show answer
Answer: A. Calcium bicarbonate
Calcium bicarbonate (Ca(HCO3)₂) is a common salt found dissolved in water that causes temporary hardness. When heated, calcium bicarbonate decomposes to form calcium carbonate, which precipitates out, reducing the hardness. Calcium carbonate (CaCO₃) itself is largely insoluble in water under normal conditions and does not dissolve significantly to cause hardness.
The principle involved in paper chromatography is
Asked in: UPSC CAPF 2019
1. Absorption
2. Partition
3. Solubility
4. Volatility
Show answer
Answer: B. Partition
The core principle of paper chromatography is the partition of solutes between the stationary phase (water on paper) and the mobile phase (solvent). While solubility in the mobile phase and interaction with the stationary phase are factors, the overall process is governed by the partition coefficient of each substance between the two phases.
Water can dissolve more substances than any other liquid because
Asked in: UPSC IAS 2021
1. it is dipolar in nature
2. it is a good conductor of heat
3. it has high value of specific heat
4. it is an oxide of hydrogen
Show answer
Answer: A. it is dipolar in nature
- Water is a polar molecule due to unequal sharing of electrons between oxygen and hydrogen atoms. - The polarity creates partial positive and negative charges on the molecule (dipole). - The dipolar nature allows water to form hydrogen bonds and to effectively hydrate and dissolve other polar and ionic substances.
If we add salt to pure water, its boiling point will
Asked in: WBPSC CS Prelims 2018
1. increase
2. decrease
3. remains same
4. None of the above
Show answer
Answer: A. increase
Adding a non-volatile solute, such as salt (sodium chloride), to a solvent like pure water increases the boiling point of the solvent. This phenomenon is known as boiling point elevation.
A non-volatile solid is added to water. Its boiling point will
Asked in: WBCS Main Paper 4 2023
1. decrease.
2. increase.
3. not change.
4. not to be predicted.
Show answer
Answer: B. increase.
This phenomenon is known as boiling point elevation, which is a colligative property. Colligative properties depend on the number of solute particles in a solution, not on their chemical nature. The presence of solute particles lowers the vapor pressure of the solvent, requiring a higher temperature to reach the boiling point (where vapor pressure equals atmospheric pressure).

Types of Solutions (e.g., Solid in Liquid, Liquid in Liquid, Gas in Liquid)

Solutions are of many types. Consider the following types of solution with an example each : (i) Gas in liquid—Vinegar (ii) Solid in liquid—Brine (iii) Solid in solid—Brass (iv) Liquid in liquid—Coca-Cola Select the correctly matched pairs using the codes given below.
Asked in: APSC CCE Prelims Exam 2023
1. (i) and (ii) only
2. (ii) and (iii) only
3. (i), (iii) and (iv) only
4. (ii), (iii) and (iv) only
Show answer
Answer: B. (ii) and (iii) only
- A solution is a homogeneous mixture. - The state of the solution is generally determined by the state of the solvent. - Solutions can be formed from components in different states: gas in liquid (soda water), solid in liquid (brine), solid in solid (alloys), liquid in liquid (alcohol in water), gas in gas (air), liquid in gas (humidity).
A homogeneous mixture contains two liquids. How are they separated?
Asked in: UPSC NDA 1 2017
1. By filtration
2. By evaporation
3. By distillation
4. By condensation
Show answer
Answer: C. By distillation
Distillation is a separation technique used to separate components of a liquid mixture by selective boiling and condensation. If the two liquids in the homogeneous mixture have different boiling points, one liquid will vaporize more readily than the other when heated. The vapor is then condensed back into a liquid and collected, achieving separation.
Refining of petroleum is carried out using which one of the following techniques?
Asked in: UPSC NDA 1 2022
1. Evaporation
2. Fractional distillation
3. Separating funnel
4. Sublimation
Show answer
Answer: B. Fractional distillation
Crude oil is a complex mixture of hydrocarbons with varying chain lengths and boiling points. Fractional distillation involves heating the crude oil and separating the vapours into different fractions at various levels of a fractionating column based on their condensation temperatures. Lighter fractions with lower boiling points rise higher in the column, while heavier fractions with higher boiling points condense lower down.
Which one of the following methods can be used to remove permanent hardness of water ?
Asked in: UPSC CAPF 2020
1. Boiling
2. Ion-exchange
3. Lime treatment
4. Bubbling sulphur dioxide gas
Show answer
Answer: B. Ion-exchange
Permanent hardness in water is caused by dissolved sulfates and chlorides of calcium and magnesium, which do not precipitate out upon boiling. The ion- exchange method, using materials like zeolite or synthetic resin, replaces the hard ions (Ca2+, Mg2+) with soft ions (usually Na+). This process is effective in removing both temporary and permanent hardness.
The method used in separating a mixture of two miscible liquids having sufficient difference in their boiling points is :
Asked in: UPSC CAPF 2023
1. Filtration
2. Solvent Extraction
3. Centrifugation
4. Simple Distillation
Show answer
Answer: D. Simple Distillation
Simple distillation is effective for separating miscible liquids with a significant difference in boiling points (typically > 25°C).
Which of the following are azeotropic mixtures?
Asked in: JUNIOR laboratory assistant 2025
1. 91% benzene, 9% water
2. 96% Ethanol, 4% water
3. 80% Toluene, 20% water
4. All of the above
Show answer
Answer: B. 96% Ethanol, 4% water
Azeotropic mixtures have a constant boiling point and composition. Ethanol and water form a positive azeotrope at approximately 95.6% ethanol by mass, boiling at 78.2 °C.

Concept of Solutions: Solute, Solvent, and Components

Definition and Characteristics of Chemical Changes (Chemical Reactions)

Definition and Characteristics of Physical Changes

Distinction between Physical and Chemical Changes

Distinguishing Solutions, Colloids, and Suspensions

Energy Changes in Chemical Reactions (Exothermic and Endothermic Processes)

Methods of Expressing Concentration of Solutions (Mass Percentage, Volume Percentage, Molarity, Molality, Parts Per Million)

Percentage,

Volume

Percentage, Molarity, Molality, Parts Per

Million)

Properties of Colloids (Tyndall Effect, Brownian Motion)

Saturated, Unsaturated, and Supersaturated Solutions

Solubility and Factors Affecting Solubility (Temperature, Pressure)

Types of Solutions (e.g., Solid in Liquid, Liquid in Liquid, Gas in Liquid)

3. Inorganic Chemistry

Practice MCQs: Physical and Chemical Changes, Solution

Concept of Solutions: Solute, Solvent, and Components

Definition and Characteristics of Chemical Changes (Chemical Reactions)

Definition and Characteristics of Physical Changes

Distinction between Physical and Chemical Changes

Distinguishing Solutions, Colloids, and Suspensions

Energy Changes in Chemical Reactions (Exothermic and Endothermic Processes)

Methods of Expressing Concentration of Solutions (Mass Percentage, Volume Percentage, Molarity, Molality, Parts Per Million)

Properties of Colloids (Tyndall Effect, Brownian Motion)

Saturated, Unsaturated, and Supersaturated Solutions

Solubility and Factors Affecting Solubility (Temperature, Pressure)

Types of Solutions (e.g., Solid in Liquid, Liquid in Liquid, Gas in Liquid)

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