Aqueous bromine reacts with methanoic acid to form hydrogen bromide and carbon dioxide gas. Br₂(aq) + HCO₂H(aq) → 2HBr(aq) + CO₂(g) The table shows the oxidation numbers of bromine and carbon in the species involved in this reaction. Br in Br₂ oxidation number 0 C in HCO₂H +2 Br in HBr −1 C in CO₂ +4

1. (a)Identify the oxidising agent in this reaction. Explain your reasoning with reference to oxidation numbers.[1]
2. (b)Suggest one change you would observe, ignoring temperature changes, when bromine reacts with methanoic acid.[1]
3. (c)(i)This reaction can be followed by measuring the concentration of bromine present in the mixture at regular time intervals. The graph shows the change in concentration of bromine against time in a reaction carried out at 20°C. [Figure X.X] Use the graph to calculate the average rate of reaction at 20°C during the first 600s. State the units of this rate of reaction. average rate of reaction units[2]
4. (c)(ii)The experiment is repeated at a temperature of 40°C. This relatively small increase in temperature produces a large increase in reaction rate. Sketch a graph, on the same axes, to show the expected results when repeating the experiment at 40°C.[1]
5. (c)(iii)The rate of reaction increases when the frequency of successful collisions between reactant particles increases. Explain why an increase in temperature produces this effect.[2]
6. (d)Complete the 'dot-and-cross' diagram, showing outer electrons only, to show the bonding in methanoic acid, HCO₂H. [Figure X.X][2]

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