Name: Rate of reaction. Class: Higher revision questions. Date: 57 minutes. Time: 56 marks. Marks: Comments: Page 1 of 24

Transcription

1 Rate of reaction Higher revision questions Name: Class: Date: Time: 57 minutes Marks: 56 marks Comments: Page of 24

2 A student investigated the rate of the reaction between magnesium and dilute hydrochloric acid. The student used the apparatus shown in Figure to collect the gas produced. Figure (a) Outline a plan to investigate how the rate of this reaction changed when the concentration of the hydrochloric acid was changed. Describe how you would do the investigation and the measurements you would make. Describe how you would make it a fair test. You do not need to write about safety precautions. (6) Page 2 of 24

3 (b) Figure 2 shows the gas syringe during one of the experiments. Figure 2 What is the volume of gas collected? Tick one box. 5.3 cm cm cm cm 3 () Page 3 of 24

4 (c) Figure 3 shows the student s results for one concentration of hydrochloric acid. Figure 3 The table below shows the student s results when the concentration was two times greater than the results on Figure 3 Time in seconds Volume of gas produced in cm Plot the results in the table above on the grid in Figure 3. Draw a line of best fit. (3) Page 4 of 24

5 (d) Give one conclusion about how the rate of reaction changed when the concentration of hydrochloric acid was changed. () (Total marks) 2 A student investigated the reaction between magnesium metal and dilute hydrochloric acid. The student placed 25 cm 3 of dilute hydrochloric acid in a conical flask and set up the apparatus as shown in the diagram. The student: took the bung out of the flask and added a single piece of magnesium ribbon 8 cm long put the bung back in the flask and started a stopwatch recorded the volume of gas collected after minute repeated the experiment using different temperatures of acid. Page 5 of 24

6 Volume = cm 3 () The student plotted his results on a graph. Temperature of acid in C (a) Write the correct state symbols in the equation. Choose from (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous. Mg (.) + 2 HCl (.) MgCl 2 (.) + H 2 (.) (2) (b) The diagram shows a gas syringe after minute. (i) What volume of gas has been collected in the gas syringe after minute? (ii) Use the graph to determine the temperature of the acid used in this experiment. Temperature = C () Page 6 of 24

7 (iii) Calculate the average rate of reaction, in cm 3 of hydrogen made per second (cm 3 /s), for this experiment. Rate of reaction = cm 3 /s (2) (c) The student s graph has been reprinted to help you answer this question. Temperature of acid in C One of the results on the graph is anomalous. (i) Draw a circle on the graph around the anomalous point. () Page 7 of 24

8 (ii) Suggest what may have happened to cause this anomalous result. Explain your answer. (2) (d) Explain how the student could improve the accuracy of the volume of gas recorded at each temperature. (3) (e) The student then used the same apparatus to measure the volume of gas produced every 0 seconds at 40 C. The student s results are shown on the graph. Page 8 of 24

9 Time in seconds The rate at which the gas was produced got faster over the first 60 seconds. The student s teacher gave two possible explanations of why the reaction got faster. Explanation There was a layer of magnesium oxide on the surface of the magnesium. The layer of magnesium oxide prevented the magnesium reacting with the acid. As the magnesium oxide reacted slowly with the acid, the magnesium was exposed to the acid and hydrogen gas was produced. Explanation 2 The reaction is exothermic, and so the temperature of the acid increased during the reaction. (i) Describe further experimental work the student could do to see if Explanation is correct. (2) Page 9 of 24

10 (ii) Describe further experimental work the student could do to see if Explanation 2 is correct. (2) (Total 6 marks) 3 A student investigates how the concentration of an acid affects the rate of a reaction. This is the method used.. Put a 3 cm piece of magnesium ribbon into a conical flask. 2. Add 50 cm 3 of 0.5 mol / dm 3 hydrochloric acid to the flask. 3. Collect and measure the volume of gas produced at 0 second intervals. 4. Repeat with different concentrations of hydrochloric acid using the same length of magnesium ribbon and volume of acid. Page 0 of 24

11 The student s results are shown in the figure below. (a) How do the results show that increasing the concentration of acid increases the rate of reaction? You must use data from the graph in your answer. (2) Page of 24

12 (b) Explain why the rate of reaction changes as the concentration of the acid increases. You should answer in terms of particles. (3) (c) Student A said that the final volume of gas collected was lower for a concentration of 0.5 mol dm 3 because the reaction had not finished. Student B said it was because all the acid had reacted. Describe further experimental work the students could do to find out which student was correct. (2) (Total 7 marks) Page 2 of 24

13 4 A student investigated the rate of reaction between sodium thiosulfate solution and dilute hydrochloric acid, as shown in Figure. The reaction produced a precipitate, which made the mixture turn cloudy. The student timed how long it took until she could no longer see the cross. She calculated the rate of the reaction. (a) The equation for the reaction is: Na 2 S 2 O 3 (aq) + 2 HCl(aq) 2 NaCl(aq) + S(s) + SO 2 (g) + H 2 O(l) Name the product that made the mixture go cloudy. () Page 3 of 24

14 (b) The student investigated the effect of changing the temperature of the sodium thiosulfate solution on the rate of reaction. She plotted her results on a graph, as shown in Figure 2. Describe the trends shown in the student s results. (2) Page 4 of 24

15 (c) The student then investigated the effect of changing the concentration of sodium thiosulfate solution on the rate of the reaction. (i) Suggest two variables the student would need to control to make sure that her results were valid. (2) (ii) From this investigation the student correctly concluded: As the concentration of sodium thiosulfate solution doubles, the rate of reaction doubles. Explain the student s conclusion in terms of particles. (3) (Total 8 marks) Page 5 of 24

16 5 Magnesium reacts with dilute sulphuric acid. magnesium + sulphuric acid magnesium sulphate + hydrogen A student measured the volume of hydrogen given off every 0 seconds. The results are shown on the graph. (a) The average rate of hydrogen production in the first 0 seconds is (60 cm 3 0 s) = 6 cm 3 /s. (i) Calculate the average rate of production of hydrogen between 30 seconds and 50 seconds. Show clearly how you work out your answer. Rate cm 3 /s (3) Page 6 of 24

17 (ii) Explain, as fully as you can, why the average rate between 30 and 50 seconds is different from the rate between 0 and 0 seconds. (2) (b) In industry, enzymes are used in both batch processes and continuous processes. Give one reason why continuous processes are usually more profitable than batch processes. () (Total 6 marks) 6 The apparatus shown in the diagram was used to investigate the rate of reaction of excess marble chips with dilute hydrochloric acid, HCl. Marble is calcium carbonate, formula CaCO 3. The salt formed is calcium chloride, CaCl 2. (a) Write a balanced equation for the reaction. (2) Page 7 of 24

18 The following results were obtained from the experiment. Time in minutes Reading on balance in g (b) (i) Plot the results and draw a graph on the axes below. (ii) Continue the graph you have drawn to show the expected reading after minutes. (3) () (iii) On the axes above, sketch a graph of the result which would be obtained if in a similar experiment the same mass of powdered marble was used instead of marble chips. (2) (Total 8 marks) Page 8 of 24

19 Mark schemes (a) Level 3 (5 6 marks): A coherent method is described with relevant detail, which demonstrates a broad understanding of the relevant scientific techniques and procedures. The steps in the method are logically ordered with the dependent and control variables correctly identified. The method would lead to the production of valid results. Level 2 (3 4 marks): The bulk of a method is described with mostly relevant detail, which demonstrates a reasonable understanding of the relevant scientific techniques and procedures. The method may not be in a completely logical sequence and may be missing some detail. Level ( 2 marks): Simple statements are made which demonstrate some understanding of some of the relevant scientific techniques and procedures. The response may lack a logical structure and would not lead to the production of valid results. 0 marks: No relevant content Indicative content remove bung and add magnesium start stopclock / timer measure volume of gas at fixed time intervals repeat with different concentrations of acid control volume of acid control initial temperature of acid control amount / mass / length / particle size of magnesium 6 (b) 6.5 cm 3 (c) (d) all points plotted correctly allow mark for 4 points plotted correctly best fit straight line drawn when the concentration of acid increased the rate of reaction increased or vice versa answer must use the terms rate of reaction linked to concentration 2 [] 2 (a) (s) (aq) (aq) (g) must be in this order 2 marks if all four correct mark if 2 or 3 correct 2 Page 9 of 24

20 (b) (i) 55 (ii) 54 (iii) 0.92 ignore units allow ecf from (b)(i) correct answer with or without working gains 2 marks ecf from volume in (b)(i) accept 2 d.p. up to calculator value if answer incorrect, allow rate = (b)(i) / 60 for mark 2 (c) (i) circle round point at (48,22) (ii) problem () and explanation () explanation must give lower volume of gas or slower reaction ignore human error unless qualified problem with bung e.g. bung not placed in firmly / quickly enough so gas lost or problem with reagent e.g. acid was diluted or acid not replaced so reaction slower or problem with temperature e.g. temperature was lower than recorded temperature so reaction slower or problem with measurement e.g. length of magnesium less than 8 cm or timed for less than a minute so less gas produced 2 Page 20 of 24

21 (d) repeat the experiment (several times) because anomalous results could be excluded and then the mean can be determined / calculated accept suggestion of alteration to method, which is explained as to why it would reduce the error, for 3 marks (e.g. place the magnesium in a container within the flask () so it can be tipped into the acid once the bung is in place (). This will prevent anomalous results or gas loss ()) ignore idea of more accurate gas syringe ignore shorter time intervals (e) (i) use clean magnesium or use magnesium without oxide coating compare results (ii) either measure the temperature of the acid before (adding magnesium) and after adding magnesium or place the conical flask in a water bath (at 40 C) () compare results () [6] 3 (a) (as concentration increases) answers must refer to data from graph to gain full marks relationship identified from the graph eg the same volume of gas is collected in a shorter time or more gas is collected in the same time or reaction reaches completion in a shorter time Page 2 of 24

22 reference to relevant data to evidence relationship eg 20 ml collected in 0 seconds at 0.5 mol / dm 3 in 6.5 s at.0 mol / dm 3 and in 4 s at 2.0 mol / dm 3 or at 0 seconds volume collected is 20 cm 3 with 0.5 mol / dm 3, 30 cm 3 with.0 mol / dm 3, 50 cm 3 with 2.0 mol / dm 3 or total volume collected reaches maximum of 00ml in 20 seconds at 2.0 mol / dm 3 but takes twice as long at.0 mol / dm 3 and at 0.5 mol / dm 3 (b) (c) reactions occur when particles collide increasing concentration means there are more particles in the same volume so there are more collisions leave for longer if gas continues to be produced student A is right or repeat with more acid () if more gas is produced student B is right () [7] 4 (a) sulfur / sulphur / S / S(s) (b) as the temperature increases, the rate of reaction increases allow two correct values for rate quoted (from graph) at different temperatures the rate of increase increases or there is an exponential relationship accept the rate of reaction increases slowly (from 20 C to 50 C) then increases more rapidly for 2 marks answer MUST be based on rate / speed of reaction Page 22 of 24

23 (c) (i) any two from: temperature (of the reactants) concentration of hydrochloric acid volume of hydrochloric acid volume of sodium thiosulfate the (size / darkness / thickness of the) cross total volume of solution. if no other marks gained, allow mark for: rate of stirring OR amount of hydrochloric acid / sodium thiosulfate OR volume of solution 2 (ii) (because as the concentration increases) the number of particles per unit volume increases or particles are closer together. idea of more particles in a given space is required for the first mark. ignore references to area. (therefore) the frequency of (successful) collisions increases allow increased chance / probability of collisions number of collisions increases is insufficient here. must mention per unit time or frequency. ignore speed of collisions. if reference to space and time missing from M and M2 but they are otherwise correct, then award mark. so the number of particles (per unit volume) doubles or (the frequency of) collisions doubles. students can score 2 marks for a qualitative explanation; the third mark is for a quantitative explanation. [8] 5 (a) (i) 2.25 correct answer gains three marks if incorrect allow mark for 2 correct readings (30 and 75) and further mark for allow e.c.f. 3 (ii) concentration of reactant(s) lower fewer collisions per second / time unit Page 23 of 24

24 (b) labour costs lower / enzymes costs lower not stop and start [6] 6 (a) CaCO 3 + 2HC CaC 2 + CO 2 + H 2 O one mark for CO 2 and H 2 O or H 2 CO 3 one mark for balancing the equation 2 (b) (i) linear suitable scale for y axis ± one small square accurate plots deduct one mark for each error plot smooth curve through the points or a line of best fit this mark requires a neat smooth curve (ii) curve becomes almost horizontal at or above do not credit a straight line reaching at mins accept a plot at (iii) steeper initial part to curve becoming nearly horizontal between and g [8] Page 24 of 24