Zinc–carbon cell, inert electrode cells, fuel cells: Practice Questions

Why are standard zinc-carbon cells generally considered primary (non-rechargeable) cells?

During the discharge of a standard zinc-carbon dry cell, the overall cathode reaction involves the reduction of
\(\text{MnO}_2\) to \(\text{Mn}_2\text{O}_3\) in the presence of \(\text{NH}_4^{+}\) ions. The overall ionic half-equation representing the primary reduction process at the carbon cathode is:

A molten carbonate fuel cell (MCFC) operates at high temperatures (around \(650^{\circ}\mathrm{C}\)) using molten lithium/potassium carbonate (\(\mathrm{LiKCO}_3\)) as the electrolyte. Pure hydrogen gas is supplied to the anode and a mixture of oxygen and carbon dioxide gases is supplied to the cathode. The electrodes are typically porous nickel structures.

The half-reactions are:

Anode: \(\mathrm{H}_2(\mathrm{g}) + \mathrm{CO}_3^{2-}(\mathrm{l}) \rightarrow \mathrm{H}_2\mathrm{O}(\mathrm{g}) + \mathrm{CO}_2(\mathrm{g}) + 2e^- \)

Cathode: \(\frac{1}{2}\mathrm{O}_2(\mathrm{g}) + \mathrm{CO}_2(\mathrm{g}) + 2e^- \rightarrow \mathrm{CO}_3^{2-}(\mathrm{l})\)

Which statement is CORRECT regarding the steady-state operation of this MCFC?

What is the primary function of manganese(IV) oxide ( \(\text{MnO}_2\) ) paste mixed with carbon powder in a standard zinc-carbon dry cell?

Consider the half-reactions in a hydrogen-oxygen fuel cell. How does the anode half-reaction differ when the electrolyte is acidic compared to when it is alkaline?

Explain why the zinc casing of a zinc–carbon cell often becomes thinner and may develop holes during discharge.

In a chemical cell containing a mixture of \( \text{Fe}^{2+}(aq) \) and \( \text{Fe}^{3+}(aq) \) ions in a single half-cell, a platinum wire is often used as an electrode. State the function of the platinum wire and explain why it is termed an 'inert electrode'.

Identify the gas supplied to the positive terminal of a hydrogen–oxygen fuel cell during its operation.

A hydrogen-oxygen fuel cell is an electrochemical device used to provide power for specific applications such as spacecraft.
(a) Identify the substance that is typically used as the fuel in this cell.
(b) State the role of the electrolyte in the operation of the fuel cell.
(c) Write the overall chemical equation for the reaction occurring within the cell during discharge.

A student sets up a chemical cell using two inert graphite electrodes. One electrode is immersed in a beaker containing a mixture of \( \text{FeCl}_2(\text{aq}) \) and \( \text{FeCl}_3(\text{aq}) \). The other electrode is immersed in a beaker containing a solution of \( \text{Br}_2(\text{aq}) \) and \( \text{KBr}(\text{aq}) \). The two beakers are connected by a salt bridge.
(a) Explain the term "inert electrode" in the context of this chemical cell.
(b) Identify the electrode (anode or cathode) where the oxidation of \( \text{Fe}^{2+} \) ions takes place.
(c) Write the overall ionic equation for the cell reaction.
(d) Predict the observable change in the beaker containing the bromine solution as the cell discharges.