Surface chemistry practice · Medium

The correct answer is B (Dialysis) because dialysis is a method specifically used to purify colloidal solutions by removing impurities.

Option D (A layer of dispersion medium) is correct because lyophilic colloids are stabilized by a solvation layer of the dispersion medium around the colloidal particles.

Option A ($\mathrm{KCl}$) is correct because it has the lowest charge among the given electrolytes, thus requiring a higher concentration to cause coagulation of the negatively charged $\mathrm{As}_2 \mathrm{S}_3$ sol.

Option D (5 g) is correct because it is the amount of solute adsorbed per gram of adsorbent calculated using the Freundlich adsorption isotherm equation with the given parameters.

Option D (250) is correct because the gold number is the mass in milligrams of the protective colloid that prevents coagulation.

Option B is correct because a liquid dispersed in a solid is called a gel, not a solid foam. Solid foam has a gas dispersed in a solid.

Option D ($NaCl$ Solution) is correct because $NaCl$ solution is a true solution, where the solute particles are too small to scatter light and exhibit the Tyndall effect.

Option C ($2.1 \mathrm{L} \mathrm{g}^{-1}$) is correct because it is calculated by finding the volume of oxygen adsorbed per gram of adsorbent using the ideal gas law.

Option B (1) is correct because 1 mole of lead nitrate ($Pb^{2+}$) is required to coagulate 2 moles of colloidal $[AgI]I^-$.

Option C is correct. The assertion about chemisorption increasing with temperature initially and then decreasing is correct, but the reason that heat keeps providing more activation energy is incorrect. After reaching a certain temperature, the kinetic energy of the adsorbate becomes too high, leading to desorption.

The correct answer is A (Methylene blue) because basic dye stuffs like methylene blue form positive sols.

Option A (Aerosol) is correct because a colloidal system of solid in gas is defined as an aerosol.

Option A (${Ba}^{2+}, 1.0$) is correct because the flocculating value is determined by the concentration of the effective ion (${Ba}^{2+}$) required for coagulation.

Option C (S-I is false & S-II is true) is correct because cod liver oil is a water-in-oil emulsion, not oil-in-water.

Option B (Combustion of coal) is correct because it doesn't involve a catalyst, unlike the other options which are heterogeneous catalytic reactions.

Option D (${\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{4 - }}$) is correct because according to the Hardy-Schulze rule, ions with higher charges are more effective in causing coagulation of colloids.

Option B (ZSM-5) is correct because ZSM-5 is a zeolite catalyst used to convert alcohols directly into gasoline in petrochemical industries.

Option B is correct. Adsorption is a spontaneous process (ΔG < 0) that results in a decrease in entropy (ΔS < 0) and is exothermic (ΔH < 0).

Option B (physical adsorption in general increases with temperature) is wrong because physical adsorption decreases with increasing temperature due to the weak van der Waals forces involved.

Option A (Low T, high P) is correct because physical adsorption is an exothermic process favored by low temperature and high pressure according to Le Chatelier's principle.

Option B (Sulphur sol) is correct because Sulphur sol is formed by the aggregation of a large number of sulphur molecules, making it a multimolecular colloid.

Option C (Non-specificity) is correct because physisorption involves weak van der Waals forces, which are universal and do not show preference for a particular gas.

Option D (25) is correct because the gold number is defined as the amount of protective colloid in milligrams required to prevent coagulation of 10 cm³ of gold sol.