A fuel cell can be made using an electrolyte of aqueous sodium hydroxide with porous electrodes which allow the passage of water, hydrogen and oxygen. State the equations for the reactions that occur at the positive and negative electrodes.

(+) electrode (cathode):

(–) electrode (anode):

Electricity can also be generated from a lead–acid storage battery. The electrolyte is a solution of sulfuric acid and the electrodes are made of lead and lead(IV) oxide. State the equations for the reactions that occur at the positive and negative electrodes.

(+) electrode (cathode):

(–) electrode (anode):

(i)     Explain why fuel cells are less damaging to the environment than nickel–cadmium batteries.

(ii)     Other than cost, state one major difference between fuel cells and nickel–cadmium cells.

(+) electrode (cathode): \({{\text{O}}_{\text{2}}} + 2{{\text{H}}_2}{\text{O}} + {\text{4}}{{\text{e}}^ - } \to {\text{4O}}{{\text{H}}^ - }\);

(–) electrode (anode): \({{\text{H}}_2} + {\text{2O}}{{\text{H}}^ - } \to {\text{2}}{{\text{H}}_2}{\text{O}} + {\text{2}}{{\text{e}}^ - }\);

(+) electrode (cathode): \({\text{Pb}}{{\text{O}}_2} + {\text{4}}{{\text{H}}^ + } + {\text{SO}}_4^{2 - } + {\text{2}}{{\text{e}}^ - } \to {\text{PbS}}{{\text{O}}_4} + {\text{2}}{{\text{H}}_2}{\text{O}}\);

(–) electrode (anode): \({\text{Pb}} + {\text{SO}}_4^{2 - } \to {\text{PbS}}{{\text{O}}_4} + {\text{2}}{{\text{e}}^ - }\);

(i)     fuel cells produce only water / Cd and Ni are toxic (heavy metals);

(ii)     fuel cells can operate continuously/do not need recharging;

fuel cells are more unwieldy/less portable/less self-contained/need supply of \({{\text{O}}_{\text{2}}}\) and \({{\text{H}}_{\text{2}}}\);

Accept opposite statements for NiCd cells.

Very few correct answers were seen in part (a).

Very few correct answers were seen in part (b).

Answers in part (c) clearly indicated the need for deeper studying of this topic.