Electrochemical cells, EMF and the electrochemical series — practice questions

Question 1 · difficulty L2 · understanding

The hydrogen electrode is dipped in a solution of $$\mathrm{pH}=3$$ at $$25^{\circ} \mathrm{C}$$. The potential of the electrode will be _________ $$\times 10^{-2} \mathrm{~V}$$. $$\left(\frac{2.303 \mathrm{RT}}{\mathrm{F}}=0.059 \mathrm{~V}\right)$$

Question 2 · difficulty L2 · understanding

In a cell, the following reactions take place \begin{aligned}\matrix{ {F{e^{2 + }} \to F{e^{3 + }} + {e^ - }} & {E_{F{e^{3 + }}/F{e^{2 + }}}^o = 0.77\,V} \cr {2{I^ - } \to {I_2} + 2{e^ - }} & {E_{{I_2}/{I^ - }}^o = 0.54\,V} \cr } \end{aligned} The standard electrode potential for the spontaneous reaction in the cell is x $$\times$$ 10 $$-$$2 V 298 K. The value of x is ____________. (Nearest Integer)

Question 3 · difficulty L2 · understanding

Given at 298 K : $$\begin{aligned} & \mathrm{E}_{\mathrm{Fe}^{2+} / \mathrm{Fe}}^{\ominus}=\mathrm{X} \text { Volt } \\ & \mathrm{E}_{\mathrm{Fe}^{3+} / \mathrm{Fe}}^{\ominus}=\mathrm{Y} \text { Volt } \end{aligned}$$ The $\mathrm{E}_{\mathrm{Fe}^{3+} / \mathrm{Fe}^{2+}}^{\ominus}$ in Volt at 298 K is given by :

• A. $2 \mathrm{X}-3 \mathrm{Y}$
• B. $3 Y-2 X$
• C. $3 \mathrm{Y}+2 \mathrm{X}$
• D. $Y+X$

Question 4 · difficulty L2 · understanding

Consider the following reduction processes : $$\begin{aligned} & \mathrm{Al}^{3+}+3 \mathrm{e}^{-} \longrightarrow \mathrm{Al}(\mathrm{~s}), \mathrm{E}^0=-1.66 \mathrm{~V} \\ & \mathrm{Fe}^{3+}+\mathrm{e}^{-} \longrightarrow \mathrm{Fe}^{2+}, \mathrm{E}^0=+0.77 \mathrm{~V} \\ & \mathrm{Co}^{3+}+\mathrm{e}^{-} \longrightarrow \mathrm{Co}^{2+}, \mathrm{E}^0=+1.81 \mathrm{~V} \\ & \mathrm{Cr}^{3+}+3 \mathrm{e}^{-} \longrightarrow \mathrm{Cr}(\mathrm{~s}), \mathrm{E}^0=-0.74 \mathrm{~V} \end{aligned}$$ The tendency to act as reducing agent decreases in the order :

• A. $\mathrm{Al}>\mathrm{Fe}^{2+}>\mathrm{Cr}>\mathrm{Co}^{2+}$
• B. $\mathrm{Al}>\mathrm{Cr}>\mathrm{Co}^{2+}>\mathrm{Fe}^{2+}$
• C. $\mathrm{Cr}>\mathrm{Fe}^{2+}>\mathrm{Al}>\mathrm{Co}^{2+}$
• D. $\mathrm{Al}>\mathrm{Cr}>\mathrm{Fe}^{2+}>\mathrm{Co}^{2+}$

Question 5 · difficulty L2 · understanding

The standard reduction potential values of some of the p-block ions are given below. Predict the one with the strongest oxidising capacity.

• A. $E^o_{\text{Sn}^{4+}/\text{Sn}^{2+}} = +1.15 \text{ V}$
• B. $E^o_{\text{Al}^{3+}/\text{Al}} = -1.66 \text{ V}$
• C. $E^o_{\text{Pb}^{4+}/\text{Pb}^{2+}} = +1.67 \text{ V}$
• D. $E^o_{\text{Tl}^{3+}/\text{Tl}} = +1.26 \text{ V}$

Question 6 · difficulty L2 · understanding

Based on the data given below : $$\begin{array}{ll} \mathrm{E}_{\mathrm{Cr}_2 \mathrm{O}_7^{2-} / \mathrm{Cr}^{3+}}^{\circ}=1.33 \mathrm{~V} & \mathrm{E}_{\mathrm{Cl}_2 / \mathrm{Cl}^{(-)}}^{\circ}=1.36 \mathrm{~V} \\ \mathrm{E}_{\mathrm{MnO}_4^{-} / \mathrm{Mn}^{2+}}^0=1.51 \mathrm{~V} & \mathrm{E}_{\mathrm{Cr}^{3+} / \mathrm{Cr}}^{\circ}=-0.74 \mathrm{~V} \end{array}$$ the strongest reducing agent is :

• A. $\mathrm{Cl}^{-}$
• B. $\mathrm{MnO}_4^{-}$
• C. $\mathrm{Cr}$
• D. $\mathrm{Mn}^{2+}$

Question 7 · difficulty L2 · understanding

One of the commonly used electrode is calomel electrode. Under which of the following categories, calomel electrode comes?

• A. Metal ion - Metal electrodes
• B. Oxidation - Reduction electrodes
• C. Metal - Insoluble Salt - Anion electrodes
• D. Gas - Ion electrodes

Question 8 · difficulty L2 · understanding

Reduction potential of ions are given below: $$\begin{array}{ccc} \mathrm{ClO}_4^{-} & \mathrm{IO}_4^{-} & \mathrm{BrO}_4^{-} \\ \mathrm{E}^{\circ}=1.19 \mathrm{~V} & \mathrm{E}^{\circ}=1.65 \mathrm{~V} & \mathrm{E}^{\circ}=1.74 \mathrm{~V} \end{array}$$ The correct order of their oxidising power is :

• A. $$\mathrm{IO}_4^{-}>\mathrm{BrO}_4^{-}>\mathrm{ClO}_4^{-}$$
• B. $$\mathrm{BrO}_4^{-}>\mathrm{ClO}_4^{-}>\mathrm{IO}_4^{-}$$
• C. $$\mathrm{ClO}_4^{-}>\mathrm{IO}_4^{-}>\mathrm{BrO}_4^{-}$$
• D. $$\mathrm{BrO}_4^{-}>\mathrm{IO}_4^{-}>\mathrm{ClO}_4^{-}$$

Question 9 · difficulty L2 · understanding

In 3d series, the metal having the highest M 2+ /M standard electrode potential is :

• A. Cr
• B. Fe
• C. Cu
• D. Zn

Question 10 · difficulty L2 · understanding

The $${\left( {{{\partial E} \over {\partial T}}} \right)_P}$$ of different types of half cells are as follows: A B C D $$1 \times {10^{ - 4}}$$ $$2 \times {10^{ - 4}}$$ $$0.1 \times {10^{ - 4}}$$ $$0.2 \times {10^{ - 4}}$$ (Where E is the electromotive force) Which of the above half cells would be preferred to be used as reference electrode?

• A. A
• B. B
• C. C
• D. D