A-Level AQA Chemistry Physical Chemistry Practicals: Iodide ions are oxidised to iodi

Question

Iodide ions are oxidised to iodine by hydrogen peroxide in acidic conditions.

H2O2(aq) + 2H+(aq) + 2I-(aq) → I2(aq) + 2H2O(l)

The rate equation for this reaction can be written as

rate = k[H2O2]^{m}[H+]^{n}

In an experiment to determine the order with respect to H+(aq), a reaction mixture is made containing H+(aq) with a concentration of 5.00 mol dm^-3.

A large excess of both H2O2 and I- is used in this reaction mixture so that the rate equation can be simplified to

rate = k'[H+]^{n}

1. Explain why the use of a large excess of H2O2 and I- means that the rate of reaction at a fixed temperature depends only on the concentration of H+(aq).

2. Samples of the reaction mixture are removed at timed intervals and titrated with alkali to determine the concentration of H+(aq).

State and explain what must be done to each sample before it is titrated with alkali.

Iodide ions are oxidised to iodine by hydrogen peroxide in acidic conditions - AQA - A-Level Chemistry - Question 1 - 2018 - Paper 3

Worked Solution & Example Answer:Iodide ions are oxidised to iodine by hydrogen peroxide in acidic conditions - AQA - A-Level Chemistry - Question 1 - 2018 - Paper 3

Explain why the use of a large excess of H2O2 and I- means that the rate of reaction at a fixed temperature depends only on the concentration of H+(aq).

State and explain what must be done to each sample before it is titrated with alkali.

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