Surface chemistry practice · Mixed difficulty

Option D (Reduction) is incorrect. Option B (Oxidation) is correct because sulphur colloid can be prepared by oxidizing H2S with bromine.

Option A is correct because enzymes exhibit high specificity, catalyzing only one or a few specific reactions due to their unique active site structure.

Option A (glue) is correct because glue forms a colloidal sol directly when shaken with the dispersion medium, classifying it as an intrinsic colloid.

Option A (${Fe}({OH})_3$ sol) is correct because ${Fe}({OH})_3$ sol is a positively charged sol, while $Au$, ${Cu}$, and ${As}_2{~S}_3$ sols are negatively charged.

Option B (Both liquids) is correct because an emulsion is a colloid where both the dispersed phase and the dispersion medium are liquids.

Option D ($\mathrm{Al}^{3+}$) is correct because, according to the Hardy-Schulze rule, ions with higher charges have greater coagulating power for colloids with opposite charges.

Option B (Liquid-solid) is correct because in butter, the dispersed phase is liquid (water/fat globules) and the dispersion medium is solid (milk solids).

Option B (${10^{ - 7}}\;\mathrm{m}\;\mathrm{ to}\;{10^{ - 9}}\;\mathrm{m}$) is correct because the size of colloidal particles typically ranges from 1 nm to 100 nm, which corresponds to ${10^{ - 9}}$ m to ${10^{ - 7}}$ m.

Option C (Both magnitude and sign of the charge on the ion) is correct because the coagulating power of an ion depends on both its charge and its sign, as per the Hardy-Schulze rule.

Option A (Both S-I & S-II are true) is correct because catalysts are more effective in powdered form due to increased surface area, which is maximized in the powdered state.

Option C (Bredig’s arc method) is correct because Bredig's arc method is specifically used to prepare colloidal solutions of metals like silver, gold, and platinum.

Option A (Gem stones) is correct because a solid sol is a colloidal solution where both the dispersed phase and the dispersion medium are solids.

Option D (electrodialysis) is correct because it uses an electric field and semi-permeable membranes to efficiently remove ionic impurities from a sol.

Option A (Starch) is correct because starch molecules are large and form macromolecular colloids in solution.

Option D (${10^{12}}$ times) is correct because enzymes are highly efficient catalysts, increasing reaction rates by factors of ${10^6}$ to ${10^{12}}$.

Option A (Which retards the rate of reaction) is correct because a negative catalyst, also known as an inhibitor, slows down the rate of a chemical reaction.

Option A (Palmitate) is correct because palmitate is a fatty acid, which is a small molecule, not a macromolecule.

Option A is correct because chemical adsorption (chemisorption) initially increases with temperature as it requires activation energy, but later decreases due to the exothermic nature of adsorption, and physical adsorption (physisorption) decreases with increasing temperature due to weaker van der Waals forces.

Option C (Stability of the colloidal particles) is correct because Zeta potential is directly related to the stability of colloidal solutions.

Option A ($AlCl_3$) is correct because according to Hardy-Schulze rule, greater the valency of the flocculating ion added, greater is its power to cause precipitation.

Option B (Adsorbent) is correct because the activated charcoal provides the surface on which the oxalic acid is adsorbed.

Option A (Lowers the activation energy) is the most direct effect of a catalyst, although it also changes the rate constant.

Option A (25) is correct because the gold number is defined as the amount of protective colloid in milligrams that prevents coagulation of 10 mL of gold solution by 1 mL of 10% NaCl solution.

Option A (Scattering and polarizing of light by small suspended particles is called Tyndall effect) is correct because the Tyndall effect is the scattering of light by particles in a colloid or suspension.

Option A is correct because colloids are indeed heterogeneous mixtures, and the size of the dispersed phase particles prevents them from forming a homogeneous mixture.

Option A is correct because a catalyst's effectiveness increases with surface area, which is maximized in finely divided form.

Option C (Scattering of blue light by sol paricles) is correct because the blue color of the sea is due to the scattering of blue light by water molecules and other particles, as scattering is inversely proportional to the fourth power of wavelength.

Option D is correct because when the dispersed phase is a gas and the dispersion medium is a solid, the colloid is called a solid foam, not just foam.

Option A (Break an egg carefully and transfer the transparent part of the content to $100 \mathrm{~mL}$ of $5 \% \mathrm{w} / \mathrm{V}$ saline solution and stir well.) is correct because egg albumin is the transparent part of the egg, and a saline solution helps stabilize the sol.

Option D (Electrophoresis) is correct because electrophoresis is defined as the movement of colloidal particles towards their respective electrodes under the influence of an electric field.