Which reference electrode is used to measure the electrode potential of other electrodes?
Standard hydrogen electrode (SHE) is the reference electrode whose electrode potential is taken to be zero. The electrode potential of other electrodes are measured with respect to it .
Consider a cell given below
$$\mathrm{Cu}\left|\mathrm{Cu}^{2+}\right|\left|\mathrm{Cl}^{-}\right| \mathrm{Cl}_{2,}, \mathrm{Pt}$$
Write the reactions that occur at anode and cathode.
Cell reaction represented in the question is composed of two half cell reactions. These reactions are as follows
At anode $\mathrm{Cu} \longrightarrow \mathrm{Cu}^{2+}+2 e^{-}$
At cathode $\mathrm{Cl}_2+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{Cl}^{-}$
Copper is getting oxidised at anode. $\mathrm{Cl}_2$ is getting reduced at cathode.
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.