6. Chemical reactions
A section of Chemistry, 0620
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A diagram of the apparatus which could be used to investigate the rate of reaction between magnesium and an excess of an acid is drawn below. 100 cm3 of acid 1.0 mol / dm3 volume of hydrogen measured every 15 seconds small piece of magnesium graduated tube hydrogen collects The magnesium kept rising to the surface. In one experiment, this was prevented by twisting the magnesium around a piece of copper. In a second experiment, the magnesium was held down by a plastic net fastened to the beaker. Suggest a reason why magnesium, which is denser than water, fl oated to the surface. Iron, zinc and copper have similar densities. Why was copper a better choice than iron or zinc to weigh down the magnesium? The only difference in the two experiments was the method used to hold down the magnesium. The results are shown below. volume of H2 / cm3 time / s magnesium held down by copper magnesium held down by plastic In which experiment did the magnesium react faster? Suggest a reason why the experiment chosen in had the faster rate. The experiment was repeated using 1.0 mol / dm3 propanoic acid instead of 1.0 mol / dm3 hydrochloric acid. Propanoic acid is a weak acid. How would the graph for propanoic acid differ from the graph for hydrochloric acid? How would the graph for propanoic acid be the same as the graph for hydrochloric acid? Give two factors which would alter the rate of this reaction. For each factor explain why it alters the rate. factor explanation factor explanation
0620_s10_qp_31
THEORY
2010
Paper 3, Variant 1
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