JEE Chemistry Surface Chemistry MCQs Set 20

Answer: (d) adsorbate

Explanation:
1. The substance that gets adsorbed (acetic acid) is the adsorbate.
2. The solid surface on which it is held (charcoal) is the adsorbent.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (a) chemisorption

Explanation:
1. Chemisorption involves chemical bonds between adsorbate and adsorbent and is irreversible and specific.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) van der Waals forces

Explanation:
1. Physisorption is caused by weak van der Waals forces.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) enthalpy is negative

Explanation:
1. Bonds/attractions form between the gas and the surface, so heat is released and \( \Delta H \) is negative.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) \( \ce{O2} \)

Explanation:
1. Easily liquefiable gases (higher critical temperature) are adsorbed more.
2. \( \ce{O2} \) has the lowest critical temperature here, so it is adsorbed least.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) decrease in enthalpy and decrease in entropy

Explanation:
1. Adsorption is exothermic (\( \Delta H \lt 0 \)) and the gas molecules become more ordered on the surface (\( \Delta S \lt 0 \)).

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) The enthalpy of adsorption is in the range 80-240 kJ/mol

Explanation:
1. Physisorption has a low enthalpy of adsorption, about 20-40 kJ/mol; 80-240 kJ/mol is typical of chemisorption.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) decrease in temperature

Explanation:
1. Physisorption is exothermic, so by Le Chatelier's principle it is favoured at low temperature.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) High temperature

Explanation:
1. Physisorption decreases with temperature because it is exothermic, so high temperature is unfavourable.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) Water on calcium chloride

Explanation:
1. Anhydrous \( \ce{CaCl2} \) takes water throughout its bulk (absorption). Water on silica gel, hydrogen on nickel and oxygen on a metal are surface (adsorption) phenomena.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) \( 1/n \)

Explanation:
1. \( \log(x/m) = \log k + \frac{1}{n}\log p \), so the slope is \( 1/n \) and the intercept is \( \log k \).

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) \( \ce{Cl2} \)

Explanation:
1. \( \ce{Cl2} \) has the highest critical temperature (417 K) among these gases, so it is the most easily liquefied and hence most adsorbed.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (a) lowers the activation energy

Explanation:
1. A catalyst provides an alternative path with lower activation energy and is regenerated at the end of the reaction.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) allow the equilibrium to be reached quickly

Explanation:
1. A catalyst speeds up the forward and backward reactions equally, so it does not change the position of equilibrium or \( K \).

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) Acid hydrolysis of methyl acetate

Explanation:
1. In acid hydrolysis of methyl acetate the reactants, the catalyst \( \ce{H+} \) and the products are all in the same (liquid) phase.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) catalytic promoter

Explanation:
1. Iron is the catalyst; molybdenum increases its activity, so it is a promoter.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (a) a liquid is dispersed in a liquid

Explanation:
1. Milk is an emulsion of fat globules (liquid) in water.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) water is dispersed in fat

Explanation:
1. Butter is a water-in-oil emulsion (water droplets dispersed in fat).

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (a) dispersion of a solid or liquid in a gas

Explanation:
1. Smoke and dust (solid in gas) and fog and mist (liquid in gas) are aerosols.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) solid solution

Explanation:
1. In an alloy the components are mixed at the atomic level, forming a solid solution.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) gel

Explanation:
1. Liquid in solid, as in cheese, butter or jellies, is a gel.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) gel

Explanation:
1. Cheese consists of a liquid dispersed in a solid medium, which is a gel.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) Air

Explanation:
1. Air is a homogeneous mixture of gases, i.e. a true solution.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) Blood

Explanation:
1. Blood contains particles of colloidal size (proteins, cells); the others are true solutions.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) associate

Explanation:
1. Above the CMC the surfactant molecules aggregate to form micelles.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.