Surface chemistry practice · Mixed difficulty

Option C ($10-40$) is correct because the heats of adsorption in physisorption typically lie in the range of 10-40 kJ/mol.

Option C ((A) is true but (R) is false) is correct because silica gel dries moist air through adsorption, not absorption. Adsorption is a surface phenomenon, while absorption involves penetration into the bulk.

Option B (Sorption) is correct because sorption is the process where both absorption and adsorption occur simultaneously.

Option D (Emulsion) is correct because vanishing cream is an example of an emulsion, specifically an oil-in-water emulsion.

Option D ($\mathrm{l}/n$ ($n$ being integer)) is correct because the slope of the Freundlich isotherm plot is 1/n, where n is an integer.

The correct answer is D (Both (1) and (3)) because both adsorption and occlusion describe the phenomenon of Pd absorbing 900 times its volume of hydrogen.

Option A (Gold sol) is correct because gold sols are typically negatively charged due to the adsorption of hydroxide ions or other negative ions on the gold surface.

Option B is correct because $CO_2$ is a heterogenous gas and is adsorbed to a greater extent by activated charcoal compared to the other options.

Option A (The adsorption sites are equivalent in their ability to adsorb the particles) is correct because this is a fundamental assumption in the Langmuir adsorption isotherm model.

Option D (An enzyme) is correct because enzymes are biological catalysts that speed up biochemical reactions.

Option B (Electro-dialysis) is correct because electro-dialysis is the process of removing dissolved impurities from a colloidal system using a suitable membrane under the influence of an electric field.

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 B ($1 {~nm}$ to $1000 {~nm}$) is correct because this is the defined size range for colloidal particles.

Option D (gel) is correct because the addition of alcohol to a saturated aqueous solution of calcium acetate results in the formation of a gel, which is a liquid dispersed in a solid.

The correct answer is C (Solid, Liquid, Lyophobic) because in a gold sol, the dispersed phase is solid gold particles, the dispersion medium is a liquid (usually water), and it is a lyophobic colloid due to the weak interaction between gold and the liquid.

Option B (A liquid dispersed in a gas) is correct because a liquid aerosol is defined as a colloidal system where liquid particles are dispersed within a gaseous medium.

Option D (Sol) is correct because a sol is defined as a colloidal system with a solid dispersed phase and a liquid dispersion medium.

Option C is correct. A finely divided catalyst has a much larger surface area, providing more active sites for the reaction to occur.

Option C (Starch and cellulose) is correct because starch and cellulose are naturally occurring polymers with high molecular weights, fitting the definition of macromolecular colloids.

Option B (Colloidal silver) is correct because colloidal silver solutions are used in eye drops due to their antiseptic and antibacterial properties.

The correct answer is B (50 mL of 1 M AgNO_3 + 50 mL of 2 M KI) because an excess of I- ions will be adsorbed onto the AgI precipitate, forming a negatively charged colloid.

Option D (Both amount and sign of the charge) is correct because according to the Hardy-Schulze rule, the coagulating power of an ion is directly proportional to its charge and depends on the sign of the charge being opposite to that of the colloidal solution.

Option D (Inhibitor) is correct because acetamide slows down the decomposition of hydrogen peroxide, acting as a negative catalyst or inhibitor.

Option B (van der waals’ forces) is correct because in multimolecular colloidal solutions, atoms or molecules are held together by weak van der Waals' forces.

Option D (Kraft’s temperature) is correct because the Kraft temperature is the minimum temperature at which micelles form.

Option B is correct because a higher activation energy implies a slower reaction rate, hence a smaller rate constant, according to the Arrhenius equation.

Option C (The droplets in emulsion are often positively charged) is correct because emulsion droplets are generally negatively charged due to preferential adsorption of negatively charged ions.

Option A (Alcohol to petrol) is correct because ZSM-5 is a zeolite catalyst used to convert alcohols directly into gasoline (petrol).

Option B (Lyophilic colloid) is correct because lyophilic colloids are solvent-loving, meaning they have a strong affinity for the dispersion medium.

Option A (Tyndall effect) is correct because the tails of comets are visible due to the scattering of light by dust particles, which is the Tyndall effect.