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Redox Reactions

Long Answer Type

171. Zinc liberates hydrogen from dilute hydrochloric acid, copper fails to do so. Explain.

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Short Answer Type

172. Sodium is regarded as an active metal, copper is inactive. Explain?

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173.

How can you increase the reduction potential of an electrode.

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174. Standard reduction potential of some electrodes are given below:

Electrode	Standard reduction potential (volts)
Cd²⁺ \| Cd	–0.40
Ni²⁺\|Ni	–0.25
2H⁺\|H₂	–0.00
Cu²⁺ \| Cu	+ 0.34
Ag⁺ \| + Ag	+0.53

Out of the metals given above which will liberate hydrogen when treated with HCl at 298K?

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175. Suggest a list of the substances where carbon can exhibit oxidation states from -4 to +4 and nitrogen from -3 to 5.

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Long Answer Type

176.
Using the standard electrode potentials given in the Table 8.1, predict if the
reaction between the following is feasible:
(a) Fe³⁺ (aq) and I^- (aq)
(b) Ag⁺(aq) and Cu(s)
(c) Fe³⁺(aq) and Cu(s)
(d) Ag(s) and Fe³⁺(aq)
(e) Br₂(aq) and Fe²⁺(aq)

a) Fe³⁺(aq) and I^-(aq)

Oxidation half-reaction is

2I^- -> I₂ +2e^-

E₀=-0.54V.

Reduction half reaction is Fe³⁺ (aq) +e^- -> Fe²⁺] x2

E₀ +.77V

2I^- +2Fe³⁺ -> I(g) +2Fe²⁺

E.M. F. =-0.54 +.077 = +0.23V

Since the EMF is positive the reaction is feasible.

b) Here Cu (s) loses electrons and Ag⁺(aq) gains electrons

Thus,

Oxidation half-cell reaction is

Cu(s) -> Cu²⁺ +2e^-]E₀ =-0.34 V

Reduction Ag⁺ +e^- -> 2Ag

E⁰_cell =-0.46V

Since E⁰_cell is positive the reaction is feasible..

c) Oxidation Cu(s) -> Cu²⁺(aq) +2e^-; E⁰ =-0.34 V

Reduction Fe³⁺ +e^- -> Fe²⁺

E⁰_cell = +0.77V

Probable cell

Cu(s), Cu²⁺:: Fe³⁺, Fe²⁺

E⁰_cell = E⁰_red (R.H.S)- E⁰_oxid(L.H.S)

=[0.77-0.34]V =0.43V

Since E⁰_cell is positive reaction is feasible

d) Ag(s) and Fe³⁺(aq)

Oxidation Ag(s) -> Ag⁺ +e^-; E⁰ =-0.80V

Reduction Fe³⁺ +e^- -> Fe²⁺, E⁰ =0.77V

E⁰_cell = -0.03V

Since E⁰_cell is negative, reaction is not feasible

e) Br₂ and Fe²⁺

Here Fe²⁺ lose electrons and Br₂ gain them.

Oxidation Fe ²⁺ -> Fe³⁺ +e^-]x 2 E₀ =0.77V

Reduction Br₂ +2e^- -> Br^-] (E⁰= +1.08 V)

E⁰_cell = +0.31 V

Reaction is 2Fe²⁺ +Br₂ –> 2Fe³⁺ +2Br^-

Since E⁰_cell is positive such that reaction is fesible

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177.

Predict the products of electrolysis in each of the following:

(i) An aqueous solution of AgNO₃ with silver electrodes.

ii)An aqueous solution AgNO₃ with platinum electrodes.

iii) A dilute solution of H₂SO₄ with platinum electrodes.

iv) An aqueous solution of CuCl₂ with platinum electrodes.

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Short Answer Type

178.

Depict the galvanic cell in which the reaction Zn(s) + 2Ag⁺ (aq) → Zn²⁺(aq) +2Ag(s)
takes place, Further show:
(i) which of the electrode is negatively charged,
(ii) the carriers of the current in the cell, and
(iii) individual reaction at each electrode.

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Multiple Choice Questions

179.

Consider the following reaction,

$xMnO subscript 4 superscript minus space plus space yC subscript 2 straight O subscript 4 superscript 2 minus end superscript space plus space zH to the power of plus space rightwards arrow xMn to the power of 2 plus end exponent space plus space 2 yCO subscript 2 space plus space straight z over 2 straight H subscript 2 straight O$
The values of x,y and z in the reaction are respectively