Ncert Solutions Chemistry Class 12th

The galvanic cell corresponding to the given redox reaction can be represented as:

Zn|Zn²⁺ _(aq)|Ag ⁺ _(aq)|Ag

• 1) Zn electrode (anode) is negatively charged because, at this electrode, Zn is oxidized to Zn²⁺, causing electron accumulation at the
• 2) Electrons (ions) are the carriers of the current in the cell and in the external circuit, current flows from Ag (cathode) to Zn (anode) which is normally opposite to the electron flow which is from anode to cathode.
• 3) At anode:

Zn _(s)⇒ Zn2 + (aq) + 2e– At cathode:

Ag + (aq) + e –⇒ Ag (s)

14.3 

D-glucose reacts with hydroxylamine (NH₂OH) to form oxime due to the presence of the aldehyde functional group (-CHO). This is due to the cyclic structure of glucose which forms an open chain structure in an aqueous medium, which then reacts to give an oxime.

But in case of pentaacetate of D-glucose, it does not form open chain structure in an aqueous medium so it does not react with NH₂OH.

K ⁺ /K = –2.93V, Ag⁺ /Ag = 0.80V, Hg²⁺/Hg = 0.79V Mg²⁺/Mg = –2.37 V, Cr³⁺/Cr = – 0.74V

A 3.2 Reducing power of metals increase with the decrease of reduction potential. Hence, the increasing order of reducing power will be as,
Ag < Hg < Cr < Mg < K
When the reduction potential is lower, the element has more tendency to get oxidized and thus more will be reducing power. The metal that has more negative electrode potential will be the one with more reducing power. Thus, here potassium (K) has the highest reducing power among the given elements.

The order in which the given metals displace each other from the solution of their salts is given by,
Mg>Al> Zn> Fe> Cu
A metal of stronger reducing power displaces another metal of weaker reducing power from its solution of salt. The order of increasing the reducing power of given metals is Cu< Fe< Zn< Algiven metals displace each other from the solution of their salts is given by, Mg>Al> Zn> Fe> Cu. This is hence arranged in decreasing order of its reactivity

Suggest two materials other than hydrogen that can be used as fuels in fuel cells.

Anode: Lead (Pb)

Cathode: a grid of lead packed with lead oxide (PbO₂)

Electrolyte: 38% solution of sulphuric acid (H₂SO₄)

The cell reactions are as follows :

Pb (s) + SO₂^-4 (aq) ⇒ PbSO₄ (s) + 2e^- (anode)

PbO₂ (s) + SO₂^-4 (aq) + 4H⁺ (aq) +2e^-⇒ PbSO₄ (s) +2H₂O (l) (cathode)

Pb (s) + PbO₂ (s) +2H₂SO₄ (aq)⇒ 2PbSO₄ (s) +2H₂O (l)

(overall cell reaction)

On charging, all these reactions will be reversed.

14.2

Lactose is a disaccharide carbohydrate (made up of two monosaccharide units) composed of β-D-galactose and β-D-glucose units. Hydrolysis breaks the glycosidic bond converting sucrose into β-D- galactose and β-D-glucose.

NOTE: But however, this reaction is so slow that it takes years for the solution of sucrose to undergo negligible change. Hence an enzyme called sucrase is added to proceed rapidly.

Cr₂O₇^2– + 14H⁺ + 6e^–⇒ 2Cr³⁺ + 7H₂O

A 3.12 

Cr₂O₇^2– + 14H⁺ + 6e^–⇒ 2Cr³⁺ + 7H₂O

For reducing one mole of Cr₂O₇^2–, 6 mole of electrons are required. Hence, 6 Faraday charges is needed. Hence, 6F = 6*96487 = 578922 C. Thus, the quantity of electricity is needed is 578922 C.