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$^{-1}$ |
Match the terms given in Column I with the items given in Column II.
| Column I | Column II | ||
|---|---|---|---|
| A. | $\wedge_m$ | 1. | Intensive property |
| B. | $E^s_{\text{cell}}$ | 2. | Depends on number of ions/volume |
| C. | $\kappa$ | 3. | Extensive property |
| D. | $\Delta_r G_{\text{cell}}$ | 4. | Increases with dilution |
A. $\rightarrow$ (4) B. $\rightarrow$ (1) C. $\rightarrow$ (2) D. $\rightarrow$ (3)
A. $\wedge_m$ (molar conductivity) is the conductivity due to number of ions furnished by one mole of electrolyte. As dilution increases number of ions present in the solution increases hence molar conductivity increases.
B. $E_{\text {cell }}^{\circ}$ of any atom/ion does not depend upon number of atom/ion, hence $E_{\text {cell }}^{\circ}$ of any atom/ion is an intensive properties.
C. $\kappa$ represents specific conductivity which depends upon number of ions present in per unit volume.
D. $\Delta_r G_{\text {cell }}$ is an extensive property as it depends upon number of particles(species).
Match the items of Column I and Column II.
| Column I | Column II | ||
|---|---|---|---|
| A. | Lead storage battery | 1. | Maximum efficiency |
| B. | Mercury cell | 2. | Prevented by galvanisation |
| C. | Fuel cell | 3. | Gives steady potential |
| D. | Rusting | 4. | Pb is anode, PbO$_2$ is cathode |
A. $\rightarrow(4)$ B. $\rightarrow$ (3) C. $\rightarrow$ (1) D. $\rightarrow$ (2)
A. Chemical reaction occurring on lead storage battery can be represented as
At anode $\mathrm{Pb}(\mathrm{s})+\mathrm{SO}_4{ }^{2-}(\mathrm{aq}) \longrightarrow \mathrm{PbSO}_4(\mathrm{~s})+2 e^{-}$
At cathode $\mathrm{PbO}_2(\mathrm{~s})+\mathrm{SO}_4^{2-}(\mathrm{aq})+4 \mathrm{H}^{+}(\mathrm{aq}) \xrightarrow{+2 e^{-}} 2 \mathrm{PbSO}_4(\mathrm{~s})+2 \mathrm{H}_2 \mathrm{O}(l)$
Thus, Pb is anode and $\mathrm{PbO}_2$ is cathode.
B. Mercury cell does not include ions during their function hence produce steady current.
C. Fuel cell has maximum efficiency as they produce energy due to combustion reaction of fuel.
D. Rusting is prevented by corrosion.