Electrochemistry Chemistry - Electrochemistry

• It is used to measure relative strengths of various oxidants and reductants.
• It is used to calculate standard cell potential.
• It is used to predict possible reactions.

I₂ + 2e^- → 2I^- ; Eº = 0.54 V

Cl₂ + 2e^- → 2Cl^- ; Eº = 1.36 V

Mn³⁺ +e^- → Mn²⁺ ; Eº = 1.50 V

Fe³⁺ + e^- → Fe²⁺ ; Eº = 0.77 V

O₂ + 4H⁺ + 4e^- → 2H₂O ; Eº = 1.23 V

1. Which of the following statements is correct?

1. Cl^- is oxidised by O₂.
2. Fe²⁺ is oxidised by iodine.
3. I^- is oxidised by chlorine.
4. Mn²⁺ is oxidised by chlorine.

2. Mn³⁺ is not stable in acidic medium, while Fe³⁺ is stable because:

1. O₂ oxidises Mn²⁺ to Mn³⁺
2. O₂ oxidises both Mn²⁺ to Mn³⁺ and Fe²⁺ to Fe³⁺
3. Fe³⁺ oxidises H₂O to O₂
4. Mn³⁺ oxidises H₂O to O₂

3. The strongest reducing agent in the aqueous solution is:

1. I^-
2. Cl^-
3. Mn²⁺
4. Fe²⁺

4. The emf for the following reaction is:

$\text{I}_2+\text{KCl}\rightleftharpoons2\text{KI}+\text{Cl}_2$

1. -0.82 V
2. +0.82 V
3. -0.73 V
4. +0.73 V

5. Which of the following statements is correct for the following reaction?

Fe³⁺ + Mn²⁺ → Fe²⁺ + Mn³⁺

1. The emf of the cell is positive.
2. Fe³⁺ oxidises Mn²⁺.
3. The reaction does not occur.
4. All are correct.

1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
3. Assertion is correct statement but reason is wrong statement.
4. Assertion is wrong statement but reason is correct statement.

1. Assertion: For concentration cell, $\text{Zn}_{(\text{s})}|\text{ Zn}^{2+}_{\text{(aq)}}||\text{ Zn}^{2+}_{(\text{aq})}|\text{ Zn}\\\ \ \ \ \ \ \ \ \ \ \ \ \text{C}_1\ \ \ \ \ \ \ \ \text{C}_2$

For spontaneous cell reaction, C₁ < C₂

Reason: For concentration cell, $\text{E}_\text{cell}=\frac{\text{RT}}{\text{nF}}\log\frac{\text{C}_2}{\text{C}_1}$

For spontaneous reaction, $\text{E}_\text{cell}=+\text{ve}\Rightarrow\text{C}_2>\text{C}_1$

2. Assertion: For the cell reaction, $\text{Zn}_{(\text{s})}+\text{Cu}^{2+}_{(\text{aq})}\xrightarrow{\ \ \ \ \ }\text{Zn}^{2+}_{(\text{aq})}+\text{Cu}_{(\text{s})}$ voltmeter gives zero reading at equilibrium.

Reason: At the equilibrium, there is no change in concentration of Cu2+ and Zn2+ ions.

3. Assertion: The Nernst equation gives the concentration dependence of emf of the cell.

Reason: In a cell, current flows from cathode to anode.

4. Assertion: Increase in the concentration of copper half cell in a cell, increases the emfofthe cell.

Reason: $\text{E}_\text{cell}=\text{E}^\circ_\text{cell}+\frac{0.059}{2}\log\frac{[\text{Cu}^{2+}]}{[\text{Zn}^{2+}]}$

5. Assertion: Electrode potential for the electrode $\frac{\text{Mn}^+}{\text{Mn}}$ with concentration is given by the expression under STP conditions.

$\text{E}=\text{E}^\circ+\frac{0.059}{\text{n}}\log[\text{Mn}^{+}]$

Reason: STP conditions require the temperature to be 273K.

1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
3. Assertion is correct statement but reason is wrong statement.
4. Assertion is wrong statement but reason is correct statement.

1. 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.

2. Assertion: The standard electrode potential of hydrogen is 0.0V.

Reason: It is by convention.

3. Assertion: The more negative is the standard reduction potential, greater is its ability to displace H₂ from acid.

Reason: Strength of reducing agent increases with the increase in negative value of the standard reduction potential.

4. 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.

5. Assertion: The absolute value of electrode potential cannot be determined experimentally.

Reason: The electrode potential values are generally determined with respect to SHE.

1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
3. Assertion is correct statement but reason is wrong statement.
4. Assertion is wrong statement but reason is correct statement.

1. Assertion: $\Delta\text{G}^\circ=-\text{nFE}^\circ$

Reason: E^º should be positive for a spontaneous reaction.

2. Assertion: An electrochemical cell can be set up only if the red ox reaction is spontaneous.

Reason: A reaction is spontaneous if free energy change is negative.

3. Assertion: For an electrochemical cell, $\Delta\text{G}<0$ and $\text{E}_\text{cell}>0.$

Reason: The given cell is non-spontaneous.

4. Assertion: Current stops flowing when E_cell = 0.

Reason: Equilibrium of the cell reaction is attained.

5. Assertion: E_cell should have a positive value for the cell to function.

Reason: E_cell = E_cathode - E_anode