Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2017 Oct/Nov Paper 5 · Variant 1

1 You are going to investigate the action of four different concentrations of an enzyme solution on milk protein. Milk contains a protein that makes it look white (opaque). When the protein is broken down, the milk becomes clear. (a) Read through the whole question and then complete the last heading in Table 1.1. [1] (b) (i) • Label three syringes E (for enzyme), M (for milk) and W (for water). • Label two test-tubes A and B. • Use syringe E to add 5.0 cm3 enzyme solution to test-tube A. • Use the same syringe to add 2.0 cm3 enzyme solution to test-tube B. • Use syringe M to add 2.0 cm3 milk to test-tube B and immediately start the stopclock. • Using the stirring rod, mix the contents of test-tube B well. • Time how long it takes for the protein to break down by observing test-tube B until the milk is clear. Use test-tube A as a comparison to help you. Record your result to the nearest whole second in row two, column four of Table 1.1. [1] (ii) • Rinse out test-tube B. • Use syringe W to add 0.5 cm3 distilled water to test-tube B. • Use syringe E to add 1.5 cm3 enzyme solution to test-tube B and mix well. • Use syringe M to add 2.0 cm3 milk to test-tube B and immediately start the stopclock. • Using the stirring rod, mix the contents of test-tube B well. • Time how long it takes for the protein to break down by observing test-tube B until the milk is clear. Use test-tube A as a comparison to help you. Record, in Table 1.1, your result to the nearest whole second. • Rinse out test-tube B. • Repeat experiment (ii) twice more, using the volumes of distilled water and enzyme solution shown in Table 1.1. Record, in Table 1.1, your results to the nearest whole second. [3] Table 1.1 volume of enzyme volume of distilled concentration of solution / cm3 water / cm3 enzyme ................................. % / ............................... 2.0 0.0 4 1.5 0.5 1.0 1.0 0.5 1.5 1 (c) The original enzyme solution has a concentration of 4%. In Table 1.1, use the values given for volume of enzyme solution and volume of distilled water to calculate the new concentrations of enzyme. Record these concentrations in Table 1.1. [1] (d) (i) On the grid provided, plot a graph of time taken for the milk to clear (vertical axis) against concentration of enzyme. Draw the best-fit straight line. [4] (ii) Use your graph to predict the time it would take for the milk to clear with a 1.5% enzyme solution. .......................................................................................................................................[1] (iii) Use your graph to describe the relationship between the concentration of enzyme and the time taken for the milk to clear. .......................................................................................................................................[1] (e) A student uses a similar method to investigate how the rate of this enzyme-catalysed reaction varies with temperature. (i) Suggest suitable temperatures for the student to use. .......................................................................................................................................[2] (ii) State two variables that the student should keep constant in this experiment. variable 1 ........................................................................................................................... variable 2 ........................................................................................................................... [1] Please turn over for Question 2.

Mark scheme: 1(a) time / s ; 1 1(b)(i) result for 4% recorded ; 1 1(b)(ii) full set of results recorded ; in whole seconds for all readings present ; increases in time down the table ; 3 1(c) 3 and 2 ; 1 1(d)(i) axes labelled with units ; suitable linear scale using at least half the grid ; all 4 points correctly plotted ± half small square ; best-fit straight line ; 4 1(d)(ii) correct reading from graph ± half small square ; 1 1(d)(iii) decreasing concentration increases time ORA ; 1 1(e)(i) all temperatures below between 0 and 100 inclusive ; at least 3 between 10 and 50 inclusive ; 2 1(e)(ii) two from: volume of milk ; same type of milk ; pH ; concentration of enzyme ; volume of enzyme ; level of clarity ; 1

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2 Notes for use in Qualitative Analysis for this question are printed on page 12. You are going to investigate the temperature change in a reaction and identify compounds H and J. H is an oxide. J is a nitrate salt. (a) (i) You must wear safety glasses for this experiment. • Place 15 cm3 distilled water into a beaker. • Measure the temperature of this water and record, in Table 2.1, the temperature T1 to the nearest 0.5 °C. • Add the sample of solid H to the water in the beaker. • Stir well and record, in Table 2.1, the highest temperature T2 of the mixture to the nearest 0.5 °C. • Keep the mixture for (a)(ii), (a)(iii) and (b)(ii). Record, in Table 2.1, your observations of the reaction. [3] Table 2.1 change in T1 / °C T2 / °C temperature / °C temperature observations (ii) • Filter the mixture from (a)(i) into a large test-tube. This is filtrate F. • Test filtrate F with Universal Indicator paper. • Keep filtrate F for (a)(iii) and (b)(ii). Record the final colour of the paper and the pH of the filtrate. final colour ......................................................................................................................... pH ...................................................................................................................................... [1] (iii) • One-third fill a test-tube with filtrate F. Keep the remainder of F for (b)(ii). • Place ten marble chips (calcium carbonate) in another test-tube. • Add about one third of a test-tube of dilute hydrochloric acid to the marble chips. • Immediately attach a delivery tube to the test-tube with the acid and marble chips and pass any gas produced into the test-tube containing filtrate F. Record your observations of the filtrate. ........................................................................................................................................... .......................................................................................................................................[1] (b) (i) Test a small amount of solution J in a test-tube by adding ammonia solution to it. Remember to add the ammonia solution slowly until it is in excess. Record your observations and identify J. observations ...................................................................................................................... ........................................................................................................................................... J is ........................................... nitrate. [3] (ii) Place about 2 cm3 solution J in a test-tube and slowly add the remainder of filtrate F from (a)(iii) until there is no further change. Record your observations. ........................................................................................................................................... .......................................................................................................................................[1] (c) (i) Calculate the change in temperature in the reaction in (a)(i). Record, in Table 2.1, the value with a plus or minus sign as appropriate. [1] (ii) Using your answer to (c)(i), state which type of reaction has been observed in (a)(i). .......................................................................................................................................[1] (iii) In (b)(ii), filtrate F is behaving like a reagent used in Qualitative Analysis. Name this reagent. .......................................................................................................................................[1] (iv) Use the results from (a)(ii), (iii) and (b)(ii) to classify the oxide H. classification of oxide H .................................................................................................[1] (v) Use all of the evidence in (a), (b) and (c) to suggest a chemical name for H. State how you have used the evidence to arrive at your answer. H is ........................................... oxide. reason ............................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... [2]

Mark scheme: 2(a)(i) both temperatures recorded AND T2 > T1 ; temperature recorded to the nearest 0.5 °C ; white mixture (not solution) / milky ; 3 2(a)(ii) blue / purple and 10–12; 1 2(a)(iii) milky / white ppt ; 1 2(b)(i) blue ppt ; dark(er) blue solution ; (J is) copper (nitrate) ; 3 2(b)(ii) (slight) blue ppt. / blue solid ; 1 2(c)(i) temperature change and sign ; 1 2(c)(ii) exothermic ; 1 2(c)(iii) sodium hydroxide ; 1 2(c)(iv) basic / alkaline ; 1 2(c)(v) (H is) calcium (oxide) ; H + water gives limewater for CO2 test in (a)(iii) / F is limewater / calcium oxide reacts exothermically with water / H and water has pH > 7 ; 2

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3 You are going to investigate how the resistance R of a filament lamp and the power P of the filament lamp depend upon the current I flowing through it. The circuit shown in Fig. 3.1 has been set up for you. V A resistance wire C 0 100 S metre rule power supply Fig. 3.1 (a) (i) • Connect the crocodile clip C to the end S (0 cm) of the resistance wire. • Switch on. • Use the voltmeter and the ammeter to measure the potential difference V across the lamp and the current I flowing through the lamp. Record, in Table 3.1, your values of V and I. • Switch off. [2] Table 3.1 position of potential current resistance power crocodile clip C difference / cm V / V I / A R / Ω P / ........... 0 20.0 40.0 60.0 80.0 (ii) Repeat the steps in (a)(i) for different positions of the crocodile clip C, by connecting it at 20.0 cm, 40.0 cm, 60.0 cm and 80.0 cm from end S. Record, in Table 3.1, your values of V and I. Remember to switch off between readings. [4] (b) If the filament lamp becomes too dim to see while you are carrying out the investigation, state how you would know that the lamp is not broken. ...............................................................................................................................................[1] (c) (i) Calculate the resistance R of the filament lamp for each pair of readings using the equation shown. V R = I Record, in Table 3.1, your values of R to 3 significant figures. [2] (ii) Explain why it is important to switch the current off between taking readings. ........................................................................................................................................... .......................................................................................................................................[1] (d) (i) Add the unit of power to the heading of the fifth column in Table 3.1. [1] (ii) Calculate the power P of the filament lamp for each pair of readings using the equation shown. P = V × I Record, in Table 3.1, your values of P. [2] (e) A student suggests that the power P of the filament lamp is directly proportional to the current I flowing through it. State whether your experimental results support this suggestion and justify your statement by reference to your results in Table 3.1. statement .................................................................................................................................. justification ................................................................................................................................ ................................................................................................................................................... [2]

Mark scheme: 3(a)(i) V < 2.5 V and I < 1.0 A ; 2 3(a)(ii) all values recorded ; V values decreasing ; I values decreasing ; either V to at least 1 d.p. or I to at least 2 d.p. ; 4 3(b) there is an ammeter reading / current still flowing ; 1 3(c)(i) all resistance values correct and correctly rounded ; all resistance values consistently to 2 or 3 significant figures ; 2 3(c)(ii) to prevent wire getting hot / resistance of wire changing / cell running down ; 1 3(d)(i) W / J per s; 1 3(d)(ii) all power values correct ; power values decreasing ; 2 3(e) no / yes (to match results) and actual values used to show relationship / reference to how P changes with I ; doubling I does not double P (for no) / doubling I doubles P (for yes) or P / I not constant (for no) or P / I constant (for yes) ; 2

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