6.2. Rate of reaction
A subsection of Chemistry, 0620, through 6. Chemical reactions
Listing 10 of 319 questions
A student investigated the reaction of zinc carbonate with hydrochloric acid. ZnCO3+ 2HCl → ZnCl 2+ CO2+ H2OShe measured the decrease in mass of the reaction mixture with time. cotton wool hydrochloric acid top pan balance pieces of zinc carbonate 200.00g Explain why the mass of the reaction mixture decreased with time. The student carried out the reaction at 20 °C using small pieces of zinc carbonate. The graph below shows the results. time / s balance reading / g Describe how the mass of the reaction mixture changes with time. How long did it take for the reaction to stop? s Calculate the decrease in mass of the reaction mixture in the fi rst 20 seconds of the reaction. g On the grid above, draw a line to show how the mass of the reaction mixture changes when the experiment is carried out at 30 °C and all other conditions remain the same. How does the rate of this reaction change when larger pieces of zinc carbonate are used? The zinc chloride formed in this reaction is a salt. Give the name of another compound of zinc which, when reacted with hydrochloric acid, makes zinc chloride. Molten zinc chloride can be electrolysed using graphite electrodes. Give the name of the products formed at the anode, the cathode.
0620_s15_qp_23
THEORY
2015
Paper 2, Variant 3
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Hydrogen is produced by the reaction between zinc and dilute sulfuricacid, H2SO4. Zn+ H2SO4→ ZnSO4+ H2A student carries out an experiment using excess zinc and dilute sulfuricacid. The student measures the volume of hydrogen produced at regular time intervals using the apparatus shown in Fig.4.1. Lumps of zinc are used. dilute sulfuric acid gas syringe lumps of zinc The rate of reaction decreases as the reaction progresses. The rate eventually becomes zero. Explain why the rate of reaction decreases as the reaction progresses. Explain why the rate of reaction eventually becomes zero. The experiment is repeated using powdered zinc instead of lumps of zinc. All other conditions remain the same. Explain, in terms of collision theory, why the rate of reaction increases if powdered zinc is used. The equation for the reaction is shown. Zn+ H2SO4→ ZnSO4+ H225.0 cm3 of 2.00 mol / dm3 H2SO4is added to excess zinc. Calculate the volume of H2 formed at room temperature and pressure (r.t.p.). The volume of one mole of any gas is 24 dm3 at r.t.p. Use the following steps. ● Calculate the number of moles of H2SO4 used.  mol ● Deduce the number of moles of H2 produced.  mol ● Calculate the volume of H2 formed at r.t.p.  dm3  Hydrogen can also be produced by the reaction of zinc with dilute hydrochloricacid. Write a symbol equation for this reaction. State the test for hydrogen gas. test positive result  
0620_s23_qp_43
THEORY
2023
Paper 4, Variant 3
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Many organic compounds which contain a halogen have chloro, bromo or iodo in their name. The following diagram shows the structure of 1-chloropropane. C H H H C C H H Cl H H Draw the structure of an isomer of this compound. Describe how 1-chloropropane could be made from propane. Suggest an explanation why the method you have described in does not produce a pure sample of 1-chloropropane. Organic halides react with water to form an alcohol and a halide ion. CH3–CH2–I + H2O → CH3–CH2–OH + I – Describe how you could show that the reaction mixture contained an iodide ion. Name the alcohol formed when 1-chloropropane reacts with water. The speed of reaction between an organic halide and water can be measured by the following method. A mixture of 10 cm3 of aqueous silver nitrate and 10 cm3 of ethanol is warmed to 60 °C. Drops of the organic halide are added and the time taken for a precipitate to form is measured. Silver ions react with the halide ions to form a precipitate of the silver halide. Ag++ X–→ AgXTypical results for four experiments, A, B, C and D, are given in the table. experiment organic halide number of drops time / min A bromobutane B bromobutane C chlorobutane D iodobutane 0.1 Explain why it takes longer to produce a precipitate in experiment A than in B. How does the order of reactivity of the organic halides compare with the order of reactivity of the halogens? Explain why the time taken to produce a precipitate would increase if the experiments were repeated at 50 °C.
0620_w12_qp_32
THEORY
2012
Paper 3, Variant 2
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A teacher demonstrated the reactivity of calcium with water. He used the apparatus shown below. water calcium gas syringe The teacher measured the volume of gas given off at various times during the reaction. He then repeated the experiment using strontium but keeping all the conditions the same. The graph obtained from the results is shown below. time / s volume of gas / cm3 calcium strontium Explain how the graph shows that strontium is more reactive than calcium. For the reaction between calcium and water, deduce the volume of gas produced in the first 50seconds. cm3 At what time was the reaction between strontium and water complete? s How do you know from the graph that the reaction between calcium and water was not complete 100 seconds after the reaction started? Suggest how the rate of reaction changes when the same mass of calcium is used but in smaller pieces. The solution formed at the end of the reaction between strontium and water is alkaline. It is a solution of strontium hydroxide. The teacher titrated this solution with hydrochloric acid using the apparatus shown below. hydrochloric acid 25 cm3 strontium hydroxide solution burette What piece of apparatus should be used to put exactly 25.0 cm3 of the strontium hydroxide solution into the flask? A few drops of litmus solution was added to the flask. Explain why litmus is added to the flask and describe what happens to the litmus as the titration proceeds. The graph below shows how the pH of the solution in the flask changes as the acid is added. volume of hydrochloric acid / cm3 pH Describe how the pH of the solution changes as the titration proceeds. What volume of acid had been added when the solution had a neutral pH? The symbol equation for the reaction is Sr(OH)2 + 2HCl → SrCl 2 + 2H2O Give the name of the salt formed in this reaction.
0620_w15_qp_21
THEORY
2015
Paper 2, Variant 1
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