Aqueous acidified iodate(V) ions, IO3¯, react with iodide ions, as shown. IO3¯ + 6H+ + 5I¯ → 3I2 + 3H2O The initial rate of this reaction is investigated. Table 3.1 shows the results obtained. [Table 3.1] The rate equation for this reaction is rate = k[IO3¯][H+]2[I−]2.

1. (a)(i)Explain what is meant by order of reaction.[1]
2. (a)(ii)Complete Table 3.2. [Table 3.2][1]
3. (a)(iii)Use your answer to (a)(ii) to sketch lines in Fig. 3.1 to show the relationship between the initial rates and the concentrations of [IO3¯] and [I¯]. [Figure 3.1][1]
4. (a)(iv)Use data from Table 3.1 to calculate the rate constant, k, for this reaction. Include the units of k.[2]
5. (a)(v)Use data from Table 3.1 to calculate the concentration of hydrogen ions, [H+], in experiment 2.[1]
6. (a)(vi)This reaction is repeated in two separate experiments. The experiments are carried out at the same temperature and with the same concentrations of I¯ and IO3¯. One experiment takes place at pH 1.0 and the other experiment takes place at pH 2.0. rate at pH 1.0 Calculate the value of . rate at pH 2.0[1]
7. (b)In aqueous solution, iron(III) ions react with iodide ions, as shown. 2Fe3+ + 2I- → 2Fe2+ + I2 The initial rate of reaction is first order with respect to Fe3+ and second order with respect to I-. The mechanism for this reaction has three steps. Each step involves only two ions reacting together. Suggest equations for the three steps of this mechanism. Identify the rate-determining step.[3]

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