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Published on: 02/06/2021
QB365 provides detailed and simple solution for every Book back Questions in class 12 Chemistry Subject. It will helps to get more idea about question pattern in every book back questions with solution.
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Questions + Answers key
Take MCQ Chemistry Test1.
The conductivity of a 0.01M solution of a 1 :1 weak electrolyte at 298K is 1.5\(\times\)10-4 S cm−1.
i) molar conductivity of the solution
ii) degree of dissociation and the dissociation constant of the weak electrolyte
Given that
\(\lambda^{0}_{cation}=248.2 \ S\) cm2 mol-1
\(\lambda^{0}_{anlon}=51.8 \ S\) cm2 mol-1
2.
A current of 1.608A is passed through 250 mL of 0.5M solution of copper sulphate for 50 minutes. Calculate the strength of Cu2+ after electrolysis assuming volume to be constant and the current efficiency is 100%.
3.
Why is AC current used instead of DC in measuring the electrolytic conductance?
4.
Reduction potential of two metals M1 and M2 are \(E^{0}_{M^{2+}_{1}|M_{1}} = -2.3V\) and \(E^{0}_{M^{2+}_{1}|M_{1}} = 0.2V\) Predict which one is better for coating the surface of iron. Given : \(\mathrm{E}_{\mathrm{Fe}^{2+} \mid \mathrm{Fe}}^{\circ}=-0.44 \mathrm{~V}\)
5.
Is it possible to store copper sulphate in an iron vessel for a long time?
Given : \(E^{0}_{Cu^{2+}|Cu} = 0.34\) V and \(E^{0}_{Fe^{2+}|Fe} = -0.44\)V.
1.
i) Molar conductivity
Given : C = 0.01 M;
\(\kappa=1.5 \times 10^{-4} \mathrm{~S} \mathrm{~cm}^{-1} \)
\(=1.5 \times 10^{-2} \mathrm{~S} \mathrm{~m}^{-1} \)
\(\lambda_{\text {cation }}^{0}=248.2 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1} \)
\(\lambda_{\text {anion }}^{0}=51.8 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1} \)
\(\Lambda_{m}^{0}=\frac{\kappa \times 10^{-3}}{C} \mathrm{~S} \mathrm{~m}^{2} \mathrm{~mol}^{-1} \)
\(=\frac{1.5 \times 10^{-2} \times 10^{-3}}{0.01} \)
\(=1.5 \times 10^{-3} \mathrm{~S} \mathrm{~m}^{2} \mathrm{~mol}^{-1}\)
ii) \(\alpha=\frac{\Lambda_{m}}{\Lambda_{m}^{0}}\)
\(\Lambda_{\mathrm{m}}^{0}=\lambda_{\text {cation }}^{0}+\lambda_{\text {anion }}^{0} \)
\(=(248.2+51.8) \mathrm{S} \mathrm{cm}^{2} \mathrm{~mol}^{-1} \)
\(=300 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1}\)
\(=300 \times 10^{-4} \mathrm{Sm}^{2} \mathrm{~mol}^{-1} \)
\(\alpha =\frac{1.5 \times 10^{-3}}{300 \times 10^{-4}}=0.05\)
iii) \(\mathrm{K}_{\mathrm{a}} =\frac{\alpha^{2} \mathrm{C}}{1-\alpha} \)
\(\mathrm{K}_{\mathrm{a}} =\frac{(0.05)^{2} \times(0.01)}{1-0.05}=2.6 \times 10^{-5} \)
(or)
\(\mathrm{K}_{\mathrm{a}} =\alpha^{2} \mathrm{C} \)
\(=(0.05)^{2} \times(0.01) \)
\(\mathrm{K}_{\mathrm{a}} =2.5 \times 10^{-5}\)
2.
Given : I = 1.608A;
t = 50 min = 50 \(\times\) 60 = 3000sec ; S = 250 mL;
C = 0.5 M ; \(\eta=100%\)%
i) Q = It (I = Q / t)
= 1.608 x 3000 = 4824 Columb
No. of Faradays of electricity \(=\frac{4824}{96500}=0.04 \mathrm{~F}\)
ii) Electrolysis of CuSO4
\(\mathrm{Cu}_{(\mathrm{aq})}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Cu}_{(\mathrm{s})}\)
\(\therefore\) 2 F electricity will deposit 1 mole of Cu2+ to Cu
\(\therefore\) 0.05 F electricity will deposit
\(x=\frac{1 \times 0.05}{2}=0.025\) mole
Initial No. of moles of Cu2+ in 250 ml of solution \(=\frac{0.5}{1000} \times 250 \) mole = 0.125 moles
\(\therefore\) No. of moles of Cu2+ after elettrolysis = 0.125 - 0.025 = 0.1 mole
\(\therefore\) concentration of Cu2+
\(=\frac{0.1}{250} \times 1000=0.4 \mathrm{M}\)
3.
(a) If we apply DC current through the conductivity cell, it will lead to the electrolysis of the solution taken in the cell.
(b) So, AC current is used for this measurement to prevent electrolysis.
4.
The oxidation potential of M1 is more +ve than the oxidation potential of Fe which indicates that it will prevent iron from rusting.
5.
\((E^{0}_{ox})_{Fe^{2+}|Fe} = -0.44\) and
\((E^{0}_{red})_{Cu^{2+}|Cu} = 0.34\)
These +ve emf values shows that iron will oxidise and copper will get reduced i.e., the vessel will dissolve. Hence it is not possible to store copper sulphate in an iron vessel.
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