Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2022 May/June Paper 6 · Variant 3

1 Catalase is an enzyme found in living cells such as celery cells. Catalase speeds up the breakdown of hydrogen peroxide into water and oxygen gas. The catalase is not used up in the reaction. A student investigates the breakdown of hydrogen peroxide using celery. Procedure The student: • adds 2 cm3 of hydrogen peroxide solution to some celery in a test-tube • assembles the apparatus shown in Fig. 1.1 to collect the oxygen gas made clamp measuring cylinder water water mixture of celery and hydrogen peroxide Fig. 1.1 • records in Table 1.1 for trial 1, the volume of gas in the measuring cylinder every 2 minutes for 10 minutes. The student repeats the procedure, recording the values for trial 2. Table 1.1 volume of gas collected / cm3 time / minutes trial 1 trial 2 average 0 0.0 0.0 0.0 2 14.0 13.5 13.8 4 18.5 17.5 6 19.2 18.8 19.0 8 20.5 19.5 20.0 10 20.5 19.5 20.0 (a) Name a piece of apparatus suitable for measuring 2 cm3 of hydrogen peroxide solution. ............................................................................................................................................. [1] (b) The hydrogen peroxide solution is corrosive. It is labelled with the symbol shown in Fig. 1.2. Fig. 1.2 State and explain a safety precaution that the student needs to take when doing the procedure. safety precaution .............................................................................................................................. explanation ....................................................................................................................................... .......................................................................................................................................................... [1] (c) Complete Table 1.1 by calculating the average volume of gas collected after 4 minutes. [1] (d) (i) On the grid, plot a graph of average volume of gas collected (vertical axis) against time. [3] (ii) Draw the best-fit smooth curve. [1] (iii) Describe the relationship between the average volume of gas collected and time. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (iv) Explain the results between 8 and 10 minutes. ........................................................................................................................................... ..................................................................................................................................... [1] (e) State one variable that the student controls so that the comparison of the two trials is fair. ............................................................................................................................................. [1] (f) Explain why repeating a procedure several times and calculating an average gives more confidence in the reliability of the results. ............................................................................................................................................. [1] (g) Describe a test to confirm the presence of oxygen. Include the observation for a positive result. test ............................................................................................................................................ observation ............................................................................................................................... [2] [Total: 14]

Mark scheme: 1(a) syringe ; 1 1(b) goggles to protect eyes / goggle to stop burns ; gloves to protect hands / gloves to stop burns ; max 1 1 1(c) 18.0; 1 1(d)(i) axes right way round and labelled with units; suitable linear scale points covering at least half the grid; plots correct  ½ small square; 3 1(d)(ii) curve from their origin and of best-fit ; 1 1(d)(iii) as time increases volume increases ; until volume becomes constant / no more gas given off ; 2 1(d)(iv) hydrogen peroxide used up ; 1 1(e) volume / concentration of peroxide ; volume of celery puree / catalase ; temperature ; pH ; batch / type of celery (puree) ; max 1 1 1(f) identifies anomalies ; 1 1(g) glowing (splint) ; relights ; 2

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2 A student investigates the nutrient content of celery and potato using Benedict’s solution, biuret solution and iodine solution. (a) Celery gives a positive result with the Benedict’s solution. Potato gives a positive result with the iodine solution. All other results are negative. Complete Table 2.1 by recording the final colours observed in each sample. Table 2.1 final colour observed final colour observed final colour observed food sample with Benedict’s with biuret solution with iodine solution solution celery potato [3] (b) State the nutrients present and the nutrients absent in each food sample. Use the information provided in (a). celery: nutrients present ....................................................................................................................... nutrients absent ........................................................................................................................ potato: nutrients present ....................................................................................................................... nutrients absent ........................................................................................................................ [3] [Total: 6]

Mark scheme: 2(a) food sample Benedict’s biuret iodine solution celery orange / red / yellow / green blue brown / yellow / orange potato blue blue blue-black 3 2(b) celery contains reducing sugar; potato contains starch; neither contain protein; 3

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3 A student investigates the pH of several solutions and their reactivity with sodium carbonate. The pH scale is shown in Fig. 3.1. pH 1 7 14 colour red orange yellow pale dark green blue purple green description strongly weakly neutral weakly strongly acidic acidic alkaline alkaline Fig. 3.1 (a) Procedure The student: • places 1 cm depth of dilute hydrochloric acid, orange juice, salt solution, lemon juice, soap solution, vinegar and sodium hydroxide solution into separate test-tubes • adds four drops of universal indicator solution to each test-tube • records in Table 3.1 the pH of each solution. Table 3.1 colour in solution pH description universal indicator dilute hydrochloric acid 1 orange juice 5 salt solution 7 lemon juice 3 soap solution 9 vinegar 4 sodium hydroxide solution 14 (i) Record in Table 3.1 the colour of each solution with the universal indicator. Use the pH scale in Fig. 3.1. [2] (ii) Record in Table 3.1 a description of each solution. Use information from Fig. 3.1. [2] (iii) Suggest why it might be difficult for the student to estimate the pH of orange juice. ........................................................................................................................................... ..................................................................................................................................... [1] (iv) When acids and alkalis react together, a neutral solution can be made. Substances which are strongly acidic and strongly alkaline can burn the skin. A student is stung by a bee. A bee sting contains a liquid with a pH of approximately 5. State which substance in Table 3.1 can be used to neutralise the liquid in the bee sting. Explain your answer. substance .......................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... [1] (b) Procedure The student: Step 1 places 3 cm depth of dilute hydrochloric acid into a boiling tube Step 2 adds 2 spatula loads of sodium carbonate to the dilute hydrochloric acid and starts a stop-watch Step 3 stops the stop-watch when the reaction stops fizzing Step 4 records in Table 3.2 this time to the nearest second. The student repeats the procedure in (b) using orange juice, salt solution, lemon juice, soap solution, vinegar and sodium hydroxide solution instead of dilute hydrochloric acid. Table 3.2 solution time for fizzing to stop / s dilute hydrochloric acid 10 orange juice salt solution no reaction lemon juice 21 soap solution no reaction vinegar sodium hydroxide solution no reaction (i) Fig 3.2 shows the readings on the stop-watch when the fizzing stops for orange juice and vinegar. 02 :25.22 00 :28.89 min sec min sec orange juice vinegar Fig. 3.2 Record in Table 3.2 these times to the nearest second. [3] (ii) The reaction which took the least time to finish fizzing is the fastest. List the solutions in order of rate of reaction starting with the most reactive. If the solutions do not react, place them together at the bottom of the list. most reactive least reactive [1] (c) Look at the pH column in Table 3.1 and the rate of reaction in (b)(ii). Describe the relationship between pH and rate of reaction with sodium carbonate. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (d) The gas given off is carbon dioxide. State the test for carbon dioxide gas. Include the observation for a positive result. test ............................................................................................................................................ observation ............................................................................................................................... [1] [Total: 13]

Mark scheme: 3(a)(i) red yellow / light orange / yellow green pale green orange dark green / dark greeny blue / green blue orange / yellow purple ;; Question Answer Marks 3(a)(ii) acid strong acid weak neutral - acid strong/intermediate/medium alkali weak acid weak/intermediate alkali strong 2 3(a)(iii) orange juice is yellow / orange / colour masks colour of indicator ; 1 3(a)(iv) soap solution and doesn’t burn skin / pH 9 / weak alkali ; 1 3(b)(i) both times in the correct place any format ; 145 ; 29 ; 3 3(b)(ii) dilute hydrochloric acid lemon juice vinegar orange juice salt solution, soap solution, sodium hydroxide solution ; 1 3(c) as pH increases the rate of reaction decreases ora ; pH of 7 and above do not react ; 2 3(d) limewater and white ppt ; 1

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4 Solid sodium carbonate does not decompose when it is heated. Sodium carbonate solid dissolves in water to form sodium carbonate solution. Sodium carbonate solution does not decompose when it is heated. Sodium carbonate solution reacts with acid to give carbon dioxide gas. You are going to plan an experiment to find out which sodium carbonate solution, A, B or C, contains the most dissolved solid sodium carbonate. You are provided with three different sodium carbonate solutions, A, B and C. You may use any common laboratory apparatus. Include in your plan: • the apparatus needed • a brief description of the method, explaining any safety precautions • the measurements you will make including how to make them as accurate as possible • the variables you will control • how you will process your results to draw a conclusion. You may include a labelled diagram if you wish. You may include a results table if you wish. You are not required to include any results. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 4 One mark from each section and any two others. apparatus Bunsen burner / spirit burner ; balance ; measuring cylinder ; method heat water to dryness ; repeat ; goggles protect eye from acid / burns / hot water spitting Question Answer Marks 4 measurements mass of empty container / water and container before heating ; mass of solid after heating ; control volume / mass of solution used ; conclusion calculate average to identify / exclude anomalies ; subtraction of masses ; most mass left has most dissolved ; OR apparatus measuring cylinder / gas syringe ; gas collection with apparatus to collect gas ; method add acid and collect gas given off ; repeat each solution ; goggles protect eye from acid / burns measurements volume of gas given off ; control volume / mass of solution used ; excess acid ; conclusion calculate average to identify / exclude anomalies ; most CO2 given off has most dissolved solid ;

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5 A student investigates the oscillations of a pendulum. The student sets up the pendulum in a clamp as shown in Fig. 5.1. Fig. 5.1 is drawn one-fifth full size. clamp l bob Fig. 5.1 The length l of the pendulum is the distance from the bottom of the clamp to the centre of the pendulum bob. (a) (i) Measure the length l of the pendulum in centimetres to the nearest 0.1 centimetre. l = ................................................... cm [1] (ii) Calculate the actual length L of the pendulum. L = ................................................... cm [1] (b) Procedure The student: • gives the bob a small sideways displacement and releases it so that it swings to and fro • measures the time for 20 complete oscillations • repeats the timing for 20 oscillations two more times. The student’s results are shown. 25.4 s 25.6 s 25.3 s (i) Calculate the average time t for 20 oscillations of the pendulum. Give your answer to three significant figures. t = ...................................................... s [2] (ii) Calculate the time T for one complete oscillation of the pendulum. Use the equation shown. t T = 20 T = ...................................................... s [1] (iii) Calculate T 2. T 2 = ..................................................... s2 [1] (c) (i) The length L in centimetres of a pendulum which has a time T for one oscillation is calculated using the equation shown. L = 25.0T 2 Use this equation and your value of T 2 from (b)(iii) to calculate a value for L. L = ................................................... cm [1] (ii) Two values are considered to be equal within the limits of experimental error if they are within 10% of each other. Compare your value of L from part (a)(ii) with the calculated value of L from (c)(i). State if your values agree within the limits of experimental error. Justify your answer with reference to your values. ........................................................................................................................................... ..................................................................................................................................... [1] (d) Procedure The student: • adjusts the string until the length L of the pendulum is double the length of L in (a)(ii) • repeats (b)(i) and (b)(ii). The student’s results are shown. 35.9 t = ............................................................ s 1.80 T = ............................................................ s The student states that the time T for one oscillation of a pendulum is proportional to the length of the pendulum. Compare the values of T in (b)(ii) and (d) to state if you agree with the student. Give a reason for your answer. statement .................................................................................................................................. reason ....................................................................................................................................... ................................................................................................................................................... [1] (e) The student holds the rule close to the pendulum to measure its length. Explain why this gives a more accurate value for the length of the pendulum. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 10]

Mark scheme: 5(a)(i) 8.0 ; 1 5(a)(ii) 40(.0) / (a)(i)  5 ; 1 5(b)(i) 25.4333; 3 sf ; 2 5(b)(ii) 1.27(s) ; 1 5(b)(iii) 1.61 ; 1 5(c)(i) 40.25 ; 1 5(c)(ii) 10 of 40 is 4 / 10 of 40.3 is 4.03 and yes within 10 ; 1 5(d) disagree and doubling l does not double T ; 1 5(e) to avoid parallax / line-of-sight errors ; 1

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6 A student investigates the temperature of the air at different distances from a lamp. The student sets up the apparatus shown in Fig. 6.1. stand metre rule lamp 0 bench Fig. 6.1 (a) The student measures the room temperature. The thermometer used is shown in Fig. 6.2. °C 30 20 Fig. 6.2 Read the thermometer and record the room temperature θR to the nearest 0.5 °C. θR = .....................................................°C [1] (b) Procedure The student: • switches on the lamp • places the thermometer bulb a horizontal distance dH = 10 mm from the lamp as shown in Fig. 6.3 thermometer stand metre rule lamp bench dH Fig. 6.3 • waits for 20 seconds • records in Table 6.1 the distance dH and the temperature θH shown by the thermometer. The student repeats for values of dH = 20 mm, 40 mm, 60 mm, 80 mm and 100 mm. (i) Record the dH values in Table 6.1. Table 6.1 dH /............ θH /............ 10 82.0 72.5 64.0 58.0 53.5 49.0 [1] (ii) Complete the column headings in Table 6.1. [1] (iii) Suggest why the student waits for 20 seconds before recording the temperature at each distance from the lamp. ........................................................................................................................................... ..................................................................................................................................... [1] (c) (i) State the relationship between the air temperature θH and the horizontal distance dH of the thermometer bulb away from the lamp. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Calculate the average decrease in temperature per millimetre as the thermometer bulb is moved from dH = 10 mm to dH = 100 mm. Use the equation shown. temperature decrease average decrease in temperature per mm = distance moved average decrease in temperature per mm = ............................................ °C / mm [2] (d) Predict the temperature reading θ when the thermometer is at a horizontal distance of 2000 mm from the lamp. θ = .................................................... °C [1]

Mark scheme: 6(a) 24.0 ; 1 6(b)(i) correct d values recorded (10) 20, 40, 60, 80, 100 ; 1 6(b)(ii) mm and °C ; 1 6(b)(iii) allow thermometer to cool down / reach steady reading / to get to minimum temperature ; 1 6(c)(i) as d increases,  decreases ; 1 6(c)(ii) decrease in temperature = 8249 / 33 ; 33/90 = 0.37 ; 2 Question Answer Marks 6(d) 24(°C) / room temperature ; 1 6(e) 3.5(°C) ; 1 6(f) don’t touch / gloves and hot lamp / burn skin / hand ; 1

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