Beatty 15.2 ROR (W2) 2023 Answers

1 Beatty Secondary School Science Department (Chemistry Unit) Chemistry 6092 Name: ___________________________________ ( ) Date: _______________ Class: 4E___ TOPIC: SPEED / RATE OF REACTION (WORKSHEET 2) – GRAPH & PLANNING Learning Objectives: (a) Suggest a suitable method for investigating the effect of a given variable on the speed of a reaction. (b) Interpret data obtained from experiments concerned with speed of reaction. Multiple-Choice Questions 1 Dilute hydrochloric acid was reacted with magnesium ribbon and the volume of hydrogen gas evolved was measured for the first 80 seconds. What was the average rate of production of hydrogen? A 0.4 cm3/s B 2.5 cm3/s C 4 cm3/s D 40 cm3/s ( A ) 2 Two reactants were mixed together in a beaker and the mass of the beaker and its contents was recorded at regular time intervals. A graph of mass plotted against time is shown below. Which of the following are possible reactants? A sodium hydroxide and hydrochloric acid B copper sulfate and zinc C copper(II) carbonate and hydrochloric acid D sodium hydroxide and copper(II) sulfate ( C )

2 3 A student adds marble chips to hydrochloric acid. The mass of flask and contents is measured at regular time intervals. Which graph shows the result? ( A ) 4 The rate of the reaction between a given mass of calcium carbonate and an excess of hydrochloric acid is studied by collecting the carbon dioxide in a gradu ated syringe. The results are shown in the graph. How much time is required for half the calcium carbonate to react? A 0.95 min B 1.5 min C 2.0 min D 3.0 min ( A )

3 5 In two separate experiments, the reaction of powdered calcium carbo nate with an excess of dilute hydrochloric acid is investigated. The powder used in experiment 1 is finer than that used in experiment 2. All other conditions are identical in both experiments. Which graph shows the results? ( D ) 6 In two se parate experiments, a substance is decomposed and the gas evolved is collected. The graph shows the total volume of gas collected against time for each experiment. Which graph shows how the speed of reaction varies with time in each experiment? ( A )

4 Use the following information to answer Questions 7 to 10. In an experiment, a strip of magnesium ribbon is reacted with excess dilute hydrochloric acid. Curve X is obtained when the volume of hydrogen gas given off during the reaction is plotted against time. Which of the following changes to the experiment would produce the graphs, A, B, C or D? 7 Only half the amount of magnesium is reacted with excess acid. ( D ) 8 The acid is diluted to half of its original concentration but is still in excess. ( C ) 9 The strip of magnesium ribbon is grounded into powder form and then reacted with the acid. ( B ) 10 The strip of magnesium ribbon is grounded into powder form and then reacted with the acid, which has been warmed. ( A ) Structured Questions 11 Hydrogen peroxide solution decomposes in the presence of a catalyst, producing oxygen gas. The rate of this reaction can be found by plotting total volume of oxygen evolved against time.

5 (a) Describe the rate of decomposition at points E, F and G. (i) E, Rate of decomposition is the highest, with the steepest / increasing gradient (ii) F, Rate of decomposition is slower, with the decreasing gradient (iii) G, Rate of decomposition is the slowest / has completed, with zero gradient (b) How does the rate of decomposition depend upon the number of molecules of hydrogen peroxide present in the solution? Rate of decomposition increases when the number of molecules of hydrogen peroxide increases. (c) Explain, in terms of reacting particles , why the rate increases when the catalyst is more finely powdered. A more finely powdered catalyst has a larger surface area. As such, there is a greater area of contact, which particles collide more frequently and the frequency of effective collisions i ncreases, increasing the rate of reaction. 12 Pieces of calcium react with a dilute acid to produce a gas. This reaction completes in five minutes. (a) List the measurements you would make to determine the speed of this reaction. Measure and record the volume of hydrogen gas produced using a gas syringe over regular fixed time intervals of 1 minute using a stopwatch. (b) On the axes below, draw a graph for the measurements made in (a) that would show how the speed of the reaction changes. (c) Describe how you would use your graph in (b) to determine the speed of reaction at two minutes. At the two minutes point, find the gradient to determine the speed of reaction. The gradient can be calculated through drawing a line of tangent at the two minutes point. time / min volume of hydrogen gas / cm3

6 13 In an experiment (Experiment I), a volume of 0.5 mol/dm3 hydrochloric acid was added to marble chips (calcium carbonate) in a flask. The marble chips were in excess. A graph of volume of gas produced against time is shown in the diagram. (a) Write the equation, with state symbols, for the reaction. CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l) (b) Explain the shape of the graph between 2 to 2½ minutes from the start of reaction. The gradient of the graph between 2 and 2½ minut es is zero as no more gas is produced. This is because the limiting reagent, hydrochloric acid is being used up. (c) State and explain the difference in the rate of reaction at ½ minute and at 1 minute from the start of the reaction. (i) difference in rate, The rate of reaction at ½ minute is faster than at 1 minute. (ii) explanation. At ½ minute, the concentration of hydrochloric acid is higher than at 1 minute. This is because as the reaction proceeds, the concentration of hydrochloric acid decreases due to the r eaction with marble chips. (d) The experiment was repeated three times, with one change in each condition. experiment change in conditions II lower temperature III 1.0 mol/dm3 acid used, but the same volume IV smaller pieces of marble chips but the same mass Label and sketch on the axes the graphs you would expect for Experiments II to IV

7 14 A student investigates the rate of reaction between solid magnesium carbonate and dilute nitric acid was by measuring the decrease in mass of the reaction mixture over a period of time. Graph X below shows the results obtained when a 5.0 g lump of magnesium carbonate was added to an excess of 2.0 mol/dm3 nitric acid. (a) Carbon dioxide is one product of the reaction between magnesium carbonate and nitric acid. Name the other two products. magnesium nitrate and water (b) Do you think the reaction between magnesium carbonate and nitric acid had finished in 30 minutes? Explain your answer. The reaction has not finished in 30 minutes. The mass of the reaction mixture continues to drop and has not reached a constant mass. (c) The experiment was repeated using another 5.0 g lump of magnesium carbonate and 1.0 mol/dm3 nitric acid. (i) Draw on the diagram above, the graph you would expect. Label this graph Y. (ii) State two conditions which would have to be kept constant in the two experiments (X and Y) to determine the effect of concentration on the rate. mass of calcium carbonate used / volume of nitric acid used / particle size (surface a rea) of calcium carbonate / temperature of the surrounding mixture. (d) Another student suggested investigating the rate of the same reaction, but using powdered magnesium carbonate. Suggest why this method may not be suitable. The time