Seaweeds absorb iodide compounds from seawater. If seaweeds are dried and heated strongly, iodine can be obtained from the ash produced. Procedure Step 1 Heat the dried seaweed strongly to burn off any organic material. Step 2 Add the ash produced in Step 1 to $$\(25 \mathrm{~cm}^{3}\)$$ of deionised water and boil for 5 minutes. Step 3 Filter off the remaining solid, collecting the colourless filtrate containing iodide ions. Step 4 Add $$\(2 \mathrm{~cm}^{3}\)$$ of dilute sulfuric acid, followed by $$\(10 \mathrm{~cm}^{3}\)$$ of ' 20 volume' hydrogen peroxide solution, $$\(\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})\)$$. Step 5 Extract the iodine formed in Step $$\(\mathbf{4}\)$$ using cyclohexane as the solvent. Step 6 Allow the cyclohexane to evaporate to leave behind iodine crystals. ' 20 volume' hydrogen peroxide solution means that $$\(1 \mathrm{dm}^{3}\)$$ of the solution produces $$\(20 \mathrm{dm}^{3}\)$$ of oxygen gas when it decomposes completely. Calculate the concentration of ' 20 volume' hydrogen peroxide solution in $$\(\mathrm{mol} \mathrm{dm}^{-3}\)$$. [Molar volume of a gas at room temperature and pressure (r.t.p.) $$\(=24 \mathrm{dm}^{3} \mathrm{~mol}^{-1}\)$$ ] (2)

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