An aqueous solution containing a mixture of 1.0 M KI and 1.0 M CaBr2 was electrolysed using unreactive electrodes - VCE - SSCE Chemistry - Question 19 - 2009 - Paper 1

To determine the reaction that is most likely to occur at the anode during electrolysis, we need to consider the reduction potentials of the species involved.

1. The reaction at the anode involves oxidation. The given options produce different species through the loss of electrons.

2. In electrolyzing an aqueous solution containing iodide (I−) and bromide (Br−) ions:

   • The oxidation of bromide ions: Ths reaction is as follows,

   $2Br^−(aq) → Br_2(aq) + 2e^−$

   • This reaction is generally favored due to the relatively lower oxidation potential for bromide compared to iodide.

3. Considering the other options:

   • The oxidation of water ($2H_2O(l) + 2e^{-} → H_2(g) + 2OH^{-}(aq)$) also competes, but usually, halide ion oxidation is more favorable.

4. Therefore, based on standard reduction potentials, the most likely reaction occurring at the anode in this case will be:

   B. $2Br^−(aq) → Br_2(aq) + 2e^−$.