CBSE 12th Standard Chemistry Subject Electrochemistry Chapter Case Study Questions 2021
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CBSE 12th Standard Chemistry Subject Electrochemistry Case Study Questions 2021
12th Standard CBSE
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Reg.No. :
Chemistry
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Read the passage given below and answer the following questions :
The potential of each electrode is known as electrode potential. Standard electrode potential is the potential when concentration of each species taking part in electrode reaction is unity and the reaction is taking place at 298 K. By convention, the standard ectrode potential of hydrogen (SHE) is 0.0 V. The electrode potential value for eacfi electrode process is a measure of relative tendency of the active species in the process to remain in the oxidisedlreduced form. The negative electrode potential means that the redox couple is stronger reducing agent than H+/H2 couple. A positive electrode potential means that the redox couple is a weaker reducing agent than the H+/H2 couple. Metals which have higher positive value of standard reduction potential form the oxides of greater thermal stability.
In these questions (i-iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(i) Assertion : An electrochemical cell can be set-up only if the redox reaction is spontaneous.
Reason : A reaction is spontaneous if the free energy change is negative.(a) Assertion and reason both are correct statements and reason is correct explanation for assertion. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement. (ii) Assertion : The standard electrode potential of hydrogen is 0.0 V.
Reason : It is by convention.(a) Assertion and reason both are correct statements and reason is correct explanation for assertion. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement. (iii) Assertion : The negative value of standard reduction potential means that reduction takes place on this electrode with reference to hydrogen electrode.
Reason : The standard electrode potential of a half cell has a fixed value.(a) Assertion and reason both are correct statements and reason is correct explanation for assertion. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement. (iv) Assertion : The absolute value of electrode potential cannot be determined experimentally.
Reason : The electrode potential values are generally determined with respect to SHE.(a) Assertion and reason both are correct statements and reason is correct explanation for assertion. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement. (a) -
Read the passage given below and answer the following questions:
Two types of conductors are generally used, metallic and electrolytic. Free electrons are the current carrier in metallic and in electrolytic conductors, free ions. Specific conductance or conductivity of an electrolytic solution is given by
\(\kappa=C \times \frac{l}{A}\)
where, C = l/R and l/A = G* (cell constant)
Molar conductance (\(\Lambda_{m}\)) and equivalent conductance (\(\Lambda_{e}\) ) of an electrolyte solution are calculated as
\(\Lambda_{m}=\frac{\kappa \times 1000}{M} \text { or } \Lambda_{e}=\frac{\kappa \times 1000}{N}\)
where, M = molarity of solution and Nis normality of solution. Molar conductance of strong electrolyte depends on the concentration.
\(\Lambda_{m}=\Lambda_{m}^{0}-b \sqrt{C}\)
\(\Lambda_{m}^{\circ}\) = molar conductance at infinite dilution, b = constant, C = conc of solution
In these questions (i-iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(i) Assertion : The molar conductivity of strong electrolyte decreases with increase in concentration.
Reason : At high concentration, migration of ions is slow(a) Assertion and reason both are correct statements and reason is correct explanation for assertion (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement (d) Assertion is wrong statement but reason is correct statement. (ii) Assertion : Equivalent conductance of all electrolytes increases with increasing concentration.
Reason : More number of ions are available per gram equivalent at higher concentration.(a) Assertion and reason both are correct statements and reason is correct explanation for assertion (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement (d) Assertion is wrong statement but reason is correct statement. (iii) Assertion : Specific conductance decreases with dilution whereas equivalent conductance increases.
Reason : On dilution, number of ions per milli litre decreases but total number of ions increases considerably(a) Assertion and reason both are correct statements and reason is correct explanation for assertion (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement (d) Assertion is wrong statement but reason is correct statement. (iv) Assertion : The ratio of specific conductivity to the observed conductance does not depend upon the concentration of the solution taken in the conductivity cell.
Reason : Specific conductivity decreases with dilution whereas observed conductance increases with dilution.(a) Assertion and reason both are correct statements and reason is correct explanation for assertion (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement (d) Assertion is wrong statement but reason is correct statement. (a) -
Read the passage given below and answer the following questions:
Electrical work done in unit time is equal to electrical potential multiplied by total charge passed. In order to obtain maximum work from a cell, the charge has to be passed reversibly. The reversible work done by a cell is equal to decrease in its Gibb's energy. Hence, Gibb's energy of reaction is given by
\(\Delta G=-n F E_{\text {cell }}\)
Hence, E is the emf of the cell and nF is the amount of energy.
In these questions (i-iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices
(i) Assertion : \(\Delta G^{\circ}=-n F E^{\circ}\)
Reason : Eo should be positive for a spontaneous reaction(a) Assertion and reason both are correct statements and reason is correct explanation for assertion (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement. (ii) Assertion : An electrochemical cell can be set up only if the redox reaction is spontaneous.
Reason : A reaction is spontaneous if free energy change is negative.(a) Assertion and reason both are correct statements and reason is correct explanation for assertion (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement. (iii) Assertion : Current stops flowing when Ecell = 0.
Reason : Equilibrium of the cell reaction is attained.(a) Assertion and reason both are correct statements and reason is correct explanation for assertion (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement. (iv) Assertion: Ecell should have a positive value for the cell to function.
Reason : Ecell = Ecathode - Eanode(a) Assertion and reason both are correct statements and reason is correct explanation for assertion (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement. (a) -
Read the passage given below and answer the following questions:
Nernst equation relates the reduction potential of an electrochemical reaction to the standard potential and activities of the chemical species undergoing oxidation and reduction. Let us consider the reaction, \(M_{(a q)}^{n+} \longrightarrow n M_{(s)}\)
For this reaction, the electrode potential measured with respect to standard hydrogen electrode can be given as
\(E_{\left(M^{n+} / M\right)}=E_{\left(M^{n+} / M\right)}^{\circ}-\frac{R T}{n F} \ln \frac{[M]}{\left[M^{n+}\right]}\)
In these questions ( i-iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.(a) Assertion and reason both are correct statements and reason is correct explanation for assertion. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion (c) Assertion is correct statement but reason is wrong statement (d) Assertion is wrong statement but reason is correct statement. (i) Assertion : For concentration cell, \(\begin{array}{c} \mathrm{Zn}_{(s)}\left|\mathrm{Zn}^{2+}{ }_{(a q)} \| \mathrm{Zn}^{2+}{ }_{(a q)}\right| \mathrm{Zn} \\ \mathrm{C}_{1} \quad \mathrm{C}_{2} \end{array}\)
For spontaneous cell reaction, C1 < C2.
Reason : For concentration cell \(E_{\text {cell }}=\frac{R T}{n F} \log \frac{C_{2}}{C_{1}}\)
For spontaneous reaction, \(E_{\text {cell }}=+\mathrm{ve} \Rightarrow C_{2}>C_{1}\)
(ii) Assertion : For the cell reaction, \(\mathrm{Zn}_{(s)}+\mathrm{Cu}_{(a q)}^{2+} \longrightarrow \mathrm{Zn}_{(a q)}^{2+}+\mathrm{Cu}_{(s)}\) voltmeter gives zero reading at equilibrium.
Reason : At the equilibrium, there is no change in concentration of Cu2+ and Zn2+ ions.
(iii) Assertion : The Nernst equation gives the concentration dependence of emf of the cell.
Reason : In a cell, current flows from cathode to anode
(iv) Assertion : Increase in the concentration of copper half cell in a cell, increases the emf of the cell
Reason : \(E_{\text {cell }}=E_{\text {cell }}^{\circ}+\frac{0.059}{2} \log \frac{\left[\mathrm{Cu}^{2+}\right]}{\left[\mathrm{Zn}^{2+}\right]}\)(a)
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CBSE 12th Standard Chemistry Subject Electrochemistry Case Study Questions 2021 Answer Keys
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(i) (b)
(ii) (a)
(iii) (d) : A negative value of standard reduction potential means that oxidation takes' place on the electrode with reference to SHE.
(iv) (a) -
(i) (a)
(ii) (d) : At higher concentration, mobility of ions decreases. Hence, conductance decreases.
(iii) (c) : Total number of ions will increase slightly on dilution (not considerably).
(iv) (b) -
(i) (b)
(ii) (b): If redox reaction is spontaneous, \(\Delta G\) is -ve and hence, Eo is positive.
\(-\Delta G^{\mathrm{o}}=n F E^{\circ} \mathrm{cell}\)
(iii) (a)
(iv) (b) -
(i) (a) : \(\log \left(\frac{C_{1}}{C_{2}}\right)<0\) for spontaneity.
∴ C1 < C2
(ii) (a)
(iii) (b)
(iv) (a)