Chemistry CUET UG 22-05-2023 Shift 3 Paper

The Freundlich adsorption isotherm is given by:

The constant factor $\frac{1}{n}$ has values between $0$ and $1$ (commonly $0.1$ to $0.5$):

• When $\frac{1}{n} = 0$, $\frac{x}{m} = k$ (adsorption is independent of pressure, saturation reached at high pressure).
• When $\frac{1}{n} = 1$, $\frac{x}{m} = kp$ (adsorption varies directly with pressure at very low pressure).

Classification of the polymers:

• Bakelite (A): Formed by step-growth condensation of phenol and formaldehyde with loss of water molecules $\rightarrow$ Condensation polymer.
• Teflon (B): Formed by chain-growth addition polymerisation of tetrafluoroethene $\rightarrow$ Addition polymer.
• Melamine formaldehyde resin (C): Formed by condensation polymerisation of melamine and formaldehyde with elimination of water $\rightarrow$ Condensation polymer.
• Nylon-2 nylon-6 (D): Biodegradable copolymer formed by condensation polymerisation of glycine and amino caproic acid $\rightarrow$ Condensation polymer.
• Buna-S (E): Formed by addition copolymerisation of 1,3-butadiene and styrene $\rightarrow$ Addition polymer.

Matching the electrochemical cells with their characteristics:

• Fuel Cell ($\text{H}_2-\text{O}_2$ fuel cell): The overall cell reaction is the combustion of hydrogen to form water: $2\text{H}_2(g) + \text{O}_2(g) \rightarrow 2\text{H}_2\text{O}(l) \rightarrow$ (A)-(III).
• Mercury Cell: The overall cell reaction does not involve any ions in solution whose concentration can change, so it gives a steady cell potential ($1.35\text{ V}$) throughout its life $\rightarrow$ (B)-(IV).
• Leclanché Cell (dry cell): The anode is a zinc container which oxidizes to zinc ions: $\text{Zn}(s) \rightarrow \text{Zn}^{2+} + 2e^- \rightarrow$ (C)-(II).
• Ni-Cd Cell: A secondary cell which can be recharged by passing electric current in reverse direction $\rightarrow$ (D)-(I).

Defect characteristics of Potassium Chloride ($\text{KCl}$):

• Schottky Defect (A): $\text{KCl}$ is an ionic solid with high coordination number and cations ($\text{K}^+$) and anions ($\text{Cl}^-$) of comparable size, making it show Schottky defect (equal numbers of cation and anion vacancies).
• Metal Excess Defect (C): When $\text{KCl}$ crystals are heated in potassium vapor, excess potassium atoms deposit on the crystal surface and $\text{Cl}^-$ diffuses out, leaving an electron trapped in the anion vacancy ($F$-centre), which imparts a violet/lilac color. Thus, $\text{KCl}$ exhibits metal excess defect.
• $\text{KCl}$ does not show Frenkel defect (due to small size difference between ions) or metal deficiency defect (typical of transition metal oxides like $\text{FeO}$).