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Date May 2010 Marks available 4 Reference code 10M.3.hl.TZ1.C3
Level HL Paper 3 Time zone TZ1
Command term Discuss Question number C3 Adapted from N/A

Question

Discuss the production of chlorine and sodium hydroxide from brine using a membrane cell. Include in your answer the materials used for the electrodes, the equations taking place at each electrode and why this method has replaced the mercury cell.

Markscheme

\(( + )\) electrode made of titanium and \(( - )\) electrode made of steel;

\(( + ){\text{ 2C}}{{\text{l}}^ - } \to {\text{C}}{{\text{l}}_2} + {\text{2}}{{\text{e}}^ - }\);

\(( - ){\text{ 2}}{{\text{H}}_2}{\text{O}} + {\text{2}}{{\text{e}}^ - } \to {{\text{H}}_2} + {\text{2O}}{{\text{H}}^ - }{\text{ / 2}}{{\text{H}}^ + } + {\text{2}}{{\text{e}}^ - } \to {{\text{H}}_2}\);

environmental as poisonous mercury leaks from mercury cell / OWTTE / membrane cell is much cheaper to run;

Examiners report

Like C1, this was a question that demanded knowledge of basic chemistry, but it was poorly done. Vague answers were given as to “toxic mercury”.

Syllabus sections

Additional higher level (AHL) » Topic 19: Redox processes » 19.1 Electrochemical cells
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