A 0.5 m aqueous solution shows ΔTf = 0.93 K. Kf of water is 1.86 K kg mol⁻¹. The van’t Hoff factor is
A 0.5
B 1
C 2
D 3
ΔTf = iKf m → i = 0.93/(1.86×0.5) = 0.93/0.93 = 1? Wait carefully: 1.86×0.5 = 0.93, so i = 0.93/0.93 = 1.
✅ Correct Answer: B. 1
Explanation: i = ΔTf/(Kf m) = 0.93/(1.86×0.5)=1.
Osmotic pressure is most useful for molar mass determination of
A volatile liquids
B electrolytes only
C polymers and proteins
D metals
For very high molar masses, ΔTb and ΔTf are too small; osmotic pressure works well.
If two solutions have same molality, then their freezing point depression (same solvent) will be same provided
A solutes have same color
B solutes are non-electrolytes
C solutes have same molar mass
D solutes are volatile
For electrolytes, dissociation changes particle number; non-electrolytes have i≈1.
For dilute solutions, osmotic pressure shows analogy with
A Dalton’s law
B Boyle’s law
C ideal gas equation
D Avogadro’s hypothesis only
πV = nRT, analogous to PV = nRT.
A solution shows ΔTb = 0.52 K. If Kb = 0.52 K kg mol⁻¹ and i = 1, then molality is
A 0.5 m
B 1.0 m
C 2.0 m
D 0.1 m
ΔTb = iKb m ⇒ m = 0.52/(1×0.52)=1.
Colligative properties depend primarily on
A chemical nature of solute
B number of solute particles
C shape of solute
D color of solvent
That’s the definition of colligative properties.
Adsorption is a
A bulk phenomenon
B surface phenomenon
C nuclear phenomenon
D purely chemical reaction
Adsorption occurs at the surface; absorption occurs in bulk.
Physical adsorption is favored when
A temperature is low and pressure is high
B temperature is high and pressure is low
C temperature is high and pressure is high
D temperature is low and pressure is low
Physical adsorption is exothermic and increases with pressure.
Chemisorption generally forms
A multilayers
B monolayer only
C infinite layers
D no layer
Chemisorption involves specific bonding at surface sites, usually monolayer.
Heat of adsorption in chemisorption is generally
A very low (≈ 5–10 kJ/mol)
B high (≈ 80–200 kJ/mol)
C zero
D negative always in magnitude and very small
Chemical bond formation releases large energy.
A good adsorbent has
A low surface area
B high surface area
C high density only
D low porosity
More surface area provides more adsorption sites.
Freundlich isotherm is represented as
A x/m = kP^(1/n)
B x/m = kP
C x/m = P/k
D x/m = nRT
Empirical relation for adsorption of gases on solids.
In homogeneous catalysis, catalyst and reactants are in
A different phases
B same phase
C solid phase only
D gas phase only
Example: NO catalyzing SO₂ oxidation in gas phase.
In heterogeneous catalysis, reaction occurs at
A center of catalyst particle
B catalyst surface
C inside solvent only
D in gas phase only
Reactants adsorb on surface active sites and react.
A promoter in catalysis
A decreases activity by blocking sites
B increases activity of catalyst
C changes equilibrium constant
D acts as reactant
Promoters enhance efficiency (e.g., Mo as promoter in Haber catalyst).
Catalyst poisoning occurs due to
A increase in surface area
B adsorption of impurities on active sites
C formation of micelles
D dilution effect
Poisons occupy sites and reduce catalytic action (e.g., As poisons Pt)
The stability of a lyophobic sol is mainly due to
A strong solvation layer
B charge on colloidal particles
C high density of particles
D low surface area
Electrostatic repulsion prevents aggregation.
Coagulation of a negatively charged sol is most effectively caused by
A anions
B cations
C neutral molecules
D solvents only
Oppositely charged ions neutralize particle charge leading to coagulation.
According to Hardy–Schulze rule, coagulating power depends on
A ionic radius only
B valency of the oppositely charged ion
C molar mass of electrolyte
D color of electrolyte
Higher valency counter-ion has greater coagulating power.
For a negatively charged sol, correct order of coagulating power is
A Na⁺ > Ca²⁺ > Al³⁺
B Al³⁺ > Ca²⁺ > Na⁺
C Ca²⁺ > Na⁺ > Al³⁺
D Na⁺ = Ca²⁺ = Al³⁺
Higher positive charge neutralizes faster and causes coagulation more strongly.
The movement of colloidal particles towards the cathode in an electric field shows particles are
A positively charged
B negatively charged
C neutral
D uncharged but heavy
Cathode is negative; positive particles migrate toward it.
The phenomenon used in Cottrell precipitator is
A dialysis
B electrophoresis
C adsorption
D osmosis
Charged smoke particles migrate and get deposited under electric field.
Micelles are formed by soaps when concentration is
A below CMC
B above CMC
C at boiling point
D at freezing point
Above critical micelle concentration, soap molecules aggregate to form micelles.
In soap micelle, the hydrophobic part is
A ionic head
B hydrocarbon tail
C water molecules
D sodium ions
Tail is non-polar and forms the core trapping oil/grease.
In soap micelle, the hydrophilic part is
A hydrocarbon tail
B ionic head
C oil droplet
D carbon chain core
The polar/ionic head stays in water and stabilizes the micelle.
Milk is best classified as
A sol
B gel
C emulsion
D foam
Fat droplets (liquid) dispersed in water (liquid).
The process of converting precipitate into colloidal form by adding electrolyte is
A coagulation
B peptization
C dialysis
D electrophoresis
Peptization: precipitate breaks into colloidal particles with help of peptizing agent.
Lyophilic sols are more stable mainly due to
A strong solvation/hydration of particles
B absence of charge
C large particle size
D low viscosity
Solvation layer prevents particles from coming close and coagulating.
Tyndall effect is due to
A refraction only
B scattering of light
C absorption of light
D fluorescence only
Colloidal particles scatter incident light, making the beam path visible.
Brownian motion helps colloids by
A increasing density
B preventing settling of particles
C causing coagulation
D decreasing charge
Random motion counters gravity and keeps particles suspended.
Dialysis is based on difference in
A boiling points
B diffusion rates through semipermeable membrane
C vapor pressures
D densities
Small ions pass through membrane; colloidal particles do not.
Ultrafiltration differs from ordinary filtration because it uses
A ordinary filter paper
B semipermeable membrane with very fine pores
C magnetic field
D high temperature
Ultrafiltration retains colloidal particles using special membranes.
The sol where dispersion medium is solid and dispersed phase is gas is
A foam
B solid foam
C aerosol
D gel
Solid foam = gas dispersed in solid (e.g., pumice stone).
The sol where dispersed phase is solid and dispersion medium is liquid is
A sol
B foam
C aerosol
D gel
Sol = solid in liquid (e.g., paints, starch sol).
The correct pair for “liquid dispersed in gas” is
A smoke
B fog
C paint
D jelly
Fog/mist is liquid droplets dispersed in air (gas).
The main cause of cleaning action of soap is
A precipitation of dirt
B emulsification of grease
C coagulation of dirt
D adsorption of water
Soap forms micelles that trap oil/grease and allow it to be washed away with water.