6.2. Rate of reaction
A subsection of Chemistry, 0620, through 6. Chemical reactions
Listing 10 of 319 questions
The organic compound 1-bromobutane reacts with excess sodium hydroxide to form butan-1-ol. A scientist studied the rate of this reaction by fi nding out how the concentration of sodium hydroxide changed with time. The graph below shows the results. 0.25 0.20 0.15 0.10 0.05 0.00 time / hours concentration of sodium hydroxide in mol / dm3 Describe how the concentration of sodium hydroxide changes with time. Determine the time it took for the concentration of sodium hydroxide to fall to 0.15 mol / dm3. At what time was the reaction complete? On the grid above, draw a line to show how the concentration of sodium hydroxide changes when the concentration of 1-bromobutane in the reaction mixture is increased. All other conditions remain the same. Increasing the concentration of 1-bromobutane increases the rate of this reaction. Suggest one other way of increasing the rate of this reaction. The concentration of aqueous sodium hydroxide can be found by titrating samples of the reaction mixture with hydrochloric acid. Describe how you would carry out this titration. In your answer, refer to: ● a burette, ● a volumetric pipette, ● an acid-base indicator solution. Hydrochloric acid is made by dissolving hydrogen chloride gas, HCl, in water. Draw a dot-and-cross diagram to show a molecule of hydrogen chloride. Show hydrogen electrons as x. Show chlorine electrons as ●.
0620_w14_qp_21
THEORY
2014
Paper 2, Variant 1
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Calcium carbonate reacts with dilute hydrochloric acid. Complete the symbol equation for this reaction. CaCO3 + HCl → CaCl 2 + CO2 + The rate of this reaction can be followed using the apparatus shown below. A B hydrochloric acid cotton wool calcium carbonate State the names of the pieces of apparatus labelled A and B. A B Explain why the mass of the reaction mixture decreases with time. The graph below shows how the mass of the reaction mixture changes with time. The calcium carbonate was in excess and large pieces of calcium carbonate were used. 100.25 100.20 100.15 100.10 100.05 100.00 time / s mass of reaction mixture / g At what time was the reaction just complete? Calculate the total loss in mass of the reaction mixture in this experiment. How does the rate of reaction change when: smaller pieces of calcium carbonate are used, the temperature is decreased, the concentration of hydrochloric acid is decreased? When heated, calcium carbonate breaks down to form calcium oxide and carbon dioxide. Which two words from the list below describe this reaction? Tick two boxes. combustion decomposition endothermic exothermic oxidation Calcium oxide is used in fl ue-gas desulfurisation. Explain how fl ue-gas desulfurisation works. Give one other use of calcium oxide.
0620_w14_qp_22
THEORY
2014
Paper 2, Variant 2
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Methanol reacts with excess hydrochloric acid to form chloromethane and water. methanol + hydrochloric acid → chloromethane + water To which homologous series does methanol belong? Complete the structure of methanol below to show its functional group. C H H H Methanol can be made from synthesis gas which contains carbon monoxide and hydrogen. Synthesis gas is made from methane. Complete the symbol equation for this reaction. CH4 + H2O → CO + H2 Suggest two hazards associated with the products of this reaction. A student investigated the rate of reaction of methanol with hydrochloric acid. The graph below shows how the concentration of hydrochloric acid changes with time. 1.0 0.8 0.6 0.4 0.2 0.0 time / hours concentration of HCl in mol / dm3 Describe how the concentration of hydrochloric acid changes with time. Deduce the concentration of hydrochloric acid when the reaction had proceeded for 15 hours. At what time was the reaction just complete? On the grid above, draw a line to show how the concentration of hydrochloric acid changes with time when the reaction takes place at a higher temperature. Hydrochloric acid is formed when hydrogen chloride gas is dissolved in water. Draw a dot-and-cross diagram to show the electron arrangement in a molecule of hydrogen chloride. Show only the outer electron shells. Show hydrogen electrons as x. Show chlorine electrons as ●.
0620_w14_qp_23
THEORY
2014
Paper 2, Variant 3
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Glucose, sucrose and starch are all carbohydrates. Their formulae are: glucose, C6H12O6, sucrose, C12H22O11, starch, (C6H10O5)n. Identify two common features in the formulae of these carbohydrates. Draw the structure of a complex carbohydrate, such as starch. The formula of glucose, can be represented by HO OH Include three glucose units in the structure. Starch hydrolyses to glucose in the presence of the enzyme, amylase. What is meant by the term enzyme? The effect of temperature on this reaction can be studied by the experiment shown below. Starch and iodine form a blue-black colour. Glucose and iodine do not form a blue-black colour. teat pipette to add a few drops of iodine water at different temperatures aqueous starch and amylase The experiment is set up as in the diagram and the time measured for the mixture to change from blue-black to colourless. The experiment is repeated at different temperatures. Typical results of this experiment are given in the table below. experiment temperature / °C time for blue-black colour to disappear / min A B C remained blue-black Put the experiments in order of reaction rate – slowest fi rst and fastest last. Explain why the reaction rates in experiments A and B are different. Suggest why the colour remains blue-black in experiment C.
0620_w14_qp_32
THEORY
2014
Paper 3, Variant 2
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Sodium chlorate(decomposes to form sodium chloride and oxygen. The rate of this reaction is very slow at room temperature provided the sodium chlorate(is stored in a dark bottle to prevent exposure to light. 2NaCl O → 2NaCl + O2 The rate of this decomposition can be studied using the following experiment. sodium chlorate(solution oxygen collects in syringe Sodium chlorate(is placed in the fl ask and 0.2 g of copper(oxide is added. This catalyses the decomposition of the sodium chlorate(and the volume of oxygen collected is measured every minute. The results are plotted to give a graph of the type shown below. volume of oxygen time Explain why the gradient of this graph decreases with time. Cobalt(oxide is a more effi cient catalyst for this reaction than copper(oxide. Sketch, on the grid, the graph for the reaction catalysed by cobalt(oxide. All other conditions were kept constant. What can you deduce from the comment that sodium chlorate(has to be shielded from light? Explain, in terms of collisions between particles, why the initial gradient would be steeper if the experiment was repeated at a higher temperature. The ions present in aqueous sodium chloride are Na+, Cl –, H+and OH–. The electrolysis of concentrated aqueous sodium chloride forms three products. They are hydrogen, chlorine and sodium hydroxide. Explain how these three products are formed. Give ionic equations for the reactions at the electrodes. If the solution of the electrolyte is stirred, chlorine reacts with sodium hydroxide to form sodium chlorate(, sodium chloride and water. Write an equation for this reaction. Cl 2 + NaOH → + +
0620_w14_qp_33
THEORY
2014
Paper 3, Variant 3
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A student investigated the reaction of lumps of iron with sulfuric acid. Fe+ H2SO4→ FeSO4+ H2She used the apparatus shown below. sulfuric acid lumps of iron water Describe how this apparatus can be used to investigate the rate of this reaction. Describe how the rate of reaction would differ if smaller lumps of iron were used. All other conditions remain the same. The student investigated the effect of temperature on the reaction rate. State three factors which the student should keep the same in each experiment. 1. 2. 3. The table shows how the rate of reaction changed with temperature. temperature / °C rate of reaction in cm3 / s 2.2 4.4 8.8 17.6 Use the information in the table to describe how the rate of reaction changed with temperature. Iron(sulfate can be prepared by adding excess iron to sulfuric acid. Describe how you could obtain pure dry crystals of iron(sulfate from the reaction mixture in the conical fl ask.
0620_w15_qp_22
THEORY
2015
Paper 2, Variant 2
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Questions Discovered
319