lodide ions in aqueous solution are oxidised to iodine by a variety of oxidising agents. One of these is the peroxodisulfate ion, $$\(\mathrm{S}_{2} \mathrm{O}_{8}{ }^{2-}\)$$, which reacts as shown. $$\[ 2 \mathrm{I}^{-}(\mathrm{aq})+\mathrm{S}_{2} \mathrm{O}_{8}^{2-}(\mathrm{aq}) \rightarrow \mathrm{I}_{2}(\mathrm{aq})+2 \mathrm{SO}_{4}{ }^{2-}(\mathrm{aq}) \]$$ Sodium thiosulfate is added to the reaction mixture to react with iodine as it is produced. When all of the thiosulfate has reacted, further iodine produced reacts with starch indicator to give a dark colour. You will carry out two experiments to investigate how the rate of this reaction is affected by changing the concentration of the peroxodisulfate ion. FA 1 is $$\(0.0200 \mathrm{moldm}^{-3}\)$$ potassium peroxodisulfate, $$\(\mathrm{K}_{2} \mathrm{~S}_{2} \mathrm{O}_{8}\)$$. FA 2 is $$\(0.00500 \mathrm{~mol} \mathrm{dm}^{-3}\)$$ sodium thiosulfate, $$\(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\)$$. FA 3 is $$\(1.00 \mathrm{moldm}^{-3}\)$$ potassium iodide, KI . FA 4 is starch indicator. Method Experiment 1 - Label one of the $$\(100 \mathrm{~cm}^{3}\)$$ beakers $$\(\mathbf{A}\)$$ and the other $$\(100 \mathrm{~cm}^{3}\)$$ beaker $$\(\mathbf{B}\)$$. - Fill one burette with FA 1. Label this burette FA 1. - Run $$\(20.00 \mathrm{~cm}^{3}\)$$ of FA 1 from the burette into beaker $$\(\mathbf{A}\)$$. - Fill the second burette with FA 2. Label this burette FA 2. - Run $$\(10.00 \mathrm{~cm}^{3}\)$$ of FA 2 from the burette into beaker B. - Use the measuring cylinder to add $$\(20.0 \mathrm{~cm}^{3}\)$$ of FA 3 to beaker B. - Add 10 drops of FA 4 to beaker B. - Add the contents of beaker $$\(\mathbf{A}\)$$ to beaker $$\(\mathbf{B}\)$$ and start timing immediately. - Stir the mixture once and place the beaker on the white tile. - Stop timing as soon as the solution turns a dark colour. - Record this time to the nearest second in the space for results. - Wash out both beakers and dry them using paper towel. Experiment 2 - Run $$\(10.00 \mathrm{~cm}^{3}\)$$ of FA 1 from the burette into beaker $$\(\mathbf{A}\)$$. - Run $$\(10.00 \mathrm{~cm}^{3}\)$$ of FA 2 from the burette into beaker $$\(\mathbf{B}\)$$. - Use the measuring cylinder to add $$\(20.0 \mathrm{~cm}^{3}\)$$ of FA 3 into beaker B. - Use the same measuring cylinder to add $$\(10.0 \mathrm{~cm}^{3}\)$$ of distilled water to beaker $$\(\mathbf{B}\)$$. - Add 10 drops of FA 4 to beaker B. - Add the contents of beaker $$\(\mathbf{A}\)$$ to beaker $$\(\mathbf{B}\)$$ and start timing immediately. - Stir the mixture once and place the beaker on the white tile. - Stop timing as soon as the solution turns a dark colour. - Record this time to the nearest second. Record all your data in a table. You should include the volume of FA 1, the volume of distilled water, the reaction time and the rate of reaction for both experiments. Use the following formula to calculate the rate of reaction. $$\[ \text { rate }=\frac{1000}{\text { reaction time }} \]$$ Results

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