PUC Science 2nd PUC Class 12 - Karnataka Board PUC Important Questions

In the complexes `[Fe(CN)_6]^(3-)` and `[pt(en) (H_2O)_2(NO_2 (Cl)^(2+)]``the respective oxidation numbers of central metal atoms are

1) +3 and +4

2) +6 and + 4

3) +6 and +3

4) +3 and + 3

Define “Molar conductivity”.

The conductivity of 0.20 M solution of KCl at 298 K is 0.025 S cm⁻¹. Calculate its molar conductivity.

State Kohlrausch Law.

Using the E° values of A and B, predict which is better for coating the surface of iron [E°(Fe⁺²/Fe) = -0.44V] to prevent corrosion and why?

Given: E° (A⁺²/A)=-2.37 V: E°(B⁺²/B)= -0.14V

The conductivity of 0.001 mol L-1 solution of CH₃COOH is 3.905× 10-5 S cm-1. Calculate its molar conductivity and degree of dissociation (α) Given λ°(H⁺)= 349.6 S cm² mol-1 and λ°(CH₃COO)= 40.9S cm²mol^-1.

Define electrochemical cell

Following reactions occur at cathode during the electrolysis of aqueous sodium chloride solution:

Na+(aq) + e⁻ ⟶ Na (s) E⁰ =  2.71 V

H+(aq) + e⁻ ⟶ `1/2`  H₂ (g) E⁰ = 0.00 V

On the basis of their standard reduction electrode potential (E⁰) values, which reaction is feasible at the cathode and why?

Why does the cell potential of mercury cell remain constant throughout its life?

Define the following terms: Molar conductivity (⋀_m)

Define the following terms: Secondary batteries

Calculate the standard cell potential of a galvanic cell in which the following reaction takes place:

\[\ce{2Cr_{(s)} + 3Cd{^{2+}_{(aq)}} -> 2Cr{^{3+}_{(aq)}} + 3Cd}\]

Calculate the Δ_rG° and equilibrium constant of the reaction.

Define conductivity for the solution of an electrolyte.

In a first order reaction x → y, 40% of the given sample of compound remains unreacted in 45 minutes. Calculate rate constant of the reaction.

Sucrose decomposes in acid solution to give glucose and fructose according to the first order rate law. The half life of the reaction is 3 hours. Calculate fraction of sucrose which will remain after 8 hours.

A reaction is second order in A and first order in B.

(i) Write the differential rate equation.

(ii) How is the rate affected on increasing the concentration of A three times?

(iii) How is the rate affected when the concentrations of both A and B are doubled?

For a first order reaction, show that time required for 99% completion is twice the time required for the completion of 90% of reaction.

(b) Rate constant ‘k’ of a reaction varies with temperature ‘T’ according to the equation:

`logk=logA-E_a/2.303R(1/T)`

Where E_a is the activation energy. When a graph is plotted for `logk Vs. 1/T` a straight line with a slope of −4250 K is obtained. Calculate ‘E_a’ for the reaction.(R = 8.314 JK⁻¹ mol⁻¹)

 A first order reaction takes 40 minutes for 30% decomposition. Calculate t_1/2 for this reaction. (Given log 1.428 = 0.1548)

For a reaction: 

Rate = k

(i) Write the order and molecularity of this reaction.

(ii) Write the unit of k.