6.2. Rate of reaction
A subsection of Chemistry, 0620, through 6. Chemical reactions
Listing 10 of 319 questions
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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The equation for the reaction between sodium thiosulfate and hydrochloric acid is given below. Na2S2O3+ 2HCl → 2NaCl + S+ SO2+ H2OThe speed of this reaction was investigated using the following experiment. A beaker containing 50 cm3 of 0.2 mol / dm3 sodium thiosulfate was placed on a black cross. 5.0 cm3 of 2.0 mol / dm3 hydrochloric acid was added and the clock was started. look down at cross on paper paper solution turns from colourless to cloudy sodium thiosulfate and hydrochloric acid cross on paper view looking down Initially the cross was clearly visible. When the solution became cloudy and the cross could no longer be seen, the clock was stopped and the time recorded. The experiment was repeated with 25 cm3 of 0.2 mol / dm3 sodium thiosulfate and 25 cm3 of water. Typical results for this experiment and a further two experiments are given in the table. experiment volume of thiosulfate / cm3 volume of water / cm3 volume of acid / cm3 total volume / cm3 time / s Explain why it is necessary to keep the total volume the same in all the experiments. Complete the table. How and why does the speed of the reaction vary from experiment 1 to 4? The idea of collisions between reacting particles is used to explain changes in the speed of reactions. Use this idea to explain the following results. volume of sodium thiosulfate / cm3 volume of water / cm3 volume of acid / cm3 temperature / °C time / s
0620_s11_qp_32
THEORY
2011
Paper 3, Variant 2
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Questions Discovered
319