Write the Nernst equation for the cell reaction in the Daniel cell. How will the $E_{\text {cell }}$ be affected when concentration of $\mathrm{Zn}^{2+}$ ions is increased?
$$\begin{aligned} \mathrm{Zn}+\mathrm{Cu}^{2+} \longrightarrow \mathrm{Zn}^{2+}+\mathrm{Cu} & \\ E_{\text {cell }} & =E_{\text {cell }}^{\circ}-\frac{0.0591}{2} \log \left[\frac{\mathrm{Zn}^{2+}}{\mathrm{Cu}^{2+}}\right] \\ E_{\text {cell }}^{\circ} & =E_{\text {cell }}^{\circ}+\frac{0.0591}{2} \log \left[\frac{\mathrm{Cu}^{2+}}{\mathrm{Zn}^{2+}}\right] \end{aligned}$$
According to this equation $E_{\text {cell }}^{\circ}$ is directly dependent on concentration of $\mathrm{Cu}^{2+}$ and inversely dependent upon concentration of $\mathrm{Zn}^{2+}$ ions.
$E_{\text {cell }}$ decreases when concentration of $\mathrm{Zn}^{2+}$ ions is increased.
What advantage do the fuel cells have over primary and secondary batteries ?
Primary batteries contain a limited amount of reactants and are discharged when the reactants have been consumed. Secondary batteries can be recharged but it take a long time. Fuel cell run continuously as long as the reactants are supplied to it and products are removed continuously.
Write the cell reaction of a lead storage battery when it is discharged. How does the density of the electrolyte change when the battery is discharged?
When a lead storage battery is discharged then the following cell reaction takes place
$$\mathrm{Pb}+\mathrm{PbO}_2+2 \mathrm{H}_2 \mathrm{SO}_4 \longrightarrow 2 \mathrm{PbSO}_4+2 \mathrm{H}_2 \mathrm{O}$$
Density of electrolyte depends upon number of constituent ions present in per unit volume of electrolyte solution. In this case density of electrolyte decreases as water is formed and sulphuric acid is consumed as the product during discharge of the battery.
Why on dilution the $\Lambda_{\mathrm{m}}$ of $\mathrm{CH}_3 \mathrm{COOH}$ increases drastically, while that of $\mathrm{CH}_3 \mathrm{COONa}$ increases gradually?
In the case of $\mathrm{CH}_3 \mathrm{COOH}$, which is a weak electrolyte, the number of ions increase on dilution due to an increase in degree of dissociation.
$$\mathrm{CH}_3 \mathrm{COOH}+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{CH}_3 \mathrm{COO}^{-}+\mathrm{H}_3 \mathrm{O}^{+}$$
In case of strong electrolyte, the number of ions remains the same but the interionic attraction decreases.
Match the terms given in Column I with the units given in Column II.
| Column I | Column II | ||
|---|---|---|---|
| A. | $\wedge_m$ | 1. | S cm$^{-1}$ |
| B. | $E_{\text{cell}}$ | 2. | m$^{-1}$ |
| C. | $\kappa$ | 3. | S cm$^2$ mol$^{-1}$ |
| D. | $G^*$ | 4. | V |
A. $\rightarrow$ (3) B. $\rightarrow$ (4) C. $\rightarrow$ (1) D. $\rightarrow(2)$
| Column I | Column II | ||
|---|---|---|---|
| A. | $\wedge_m$ | 1. | S cm$^2$ mol$^{-1}$ |
| B. | $E_{\text{cell}}$ | 2. | V |
| C. | $\kappa$ (conductivity) | 3. | S cm$^{-1}$ |
| D. | $G^*=\frac{l}{a}$ | 4. | m$^{-1}$ |