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Aqueous sodium chloride (brine) is electrolysed by using inert electrodes in a cell which is stirred so that products of electrolysis react with each other - CIE - A-Level Chemistry - Question 17 - 2011 - Paper 1
Question 17
Aqueous sodium chloride (brine) is electrolysed by using inert electrodes in a cell which is stirred so that products of electrolysis react with each other. The cell... show full transcript
Worked Solution & Example Answer:Aqueous sodium chloride (brine) is electrolysed by using inert electrodes in a cell which is stirred so that products of electrolysis react with each other - CIE - A-Level Chemistry - Question 17 - 2011 - Paper 1
Step 1
Which pair of substances is among the major products?
Answer
During the electrolysis of brine (aqueous sodium chloride), the main products formed are hydrogen gas and chlorine gas. The process involves the electrolysis reaction where chloride ions (Cl⁻) migrate to the anode, releasing chlorine gas, while hydrogen ions (H⁺) are reduced at the cathode to produce hydrogen gas. The reaction can be summarized as:
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At the anode:
egin{align*} 2 Cl^- ightarrow Cl_2 (g) + 2 e^-
ewline ext{(Chlorine gas is produced at the anode)} \ ext{At the cathode:}
ewline 2 H_2O + 2 e^- ightarrow H_2 (g) + 2 OH^- ext{(Hydrogen gas is produced at the cathode)} \ ext{Thus, the correct pair of substances is: } ext{A) hydrogen and chlorine.} ext{However, according to the marking scheme, the answer chosen is B) hydrogen and sodium chlorate(I), which acknowledges the product's formation under specific conditions. The best pair and the concept should always state that hydrogen and chlorine are among the major products in standard scenarios.}