Cambridge IGCSE Physical Science 0652 — 2020 Oct/Nov Paper 6 · Variant 1

1 A student investigates the reaction between magnesium ribbon and hydrochloric acid. When magnesium reacts with hydrochloric acid, hydrogen gas is given off. The magnesium ribbon gets smaller as it reacts and, if the acid is in excess, the magnesium reacts until the ribbon can no longer be seen. (a) Procedure The student: • measures 25 cm3 of hydrochloric acid using a measuring cylinder and pours it into a boiling tube • measures the initial temperature of the hydrochloric acid and records this temperature to the nearest 0.5 °C in Table 1.1 • adds one piece of magnesium ribbon to the hydrochloric acid in the boiling tube and measures the highest temperature reached. The student records this temperature to the nearest 0.5 °C in Table 1.1 • rinses the boiling tube and thermometer • repeats the procedure using 2, 3, 4 and 5 pieces of magnesium ribbon. All of the pieces of magnesium ribbon are the same shape and size. (i) Fig 1.1 shows the thermometer readings for the highest temperature reached when 2 pieces of magnesium ribbon are added and when 5 pieces of magnesium ribbon are added. Record these temperatures in Table 1.1. [2] °C °C 40 60 30 50 20 40 2 pieces of 5 pieces of magnesium added magnesium added Fig. 1.1 Table 1.1 number of pieces of initial temperature of highest temperature temperature rise / °C magnesium ribbon hydrochloric acid / °C reached / °C 1 22.0 27.5 5.5 2 22.0 3 22.0 38.0 16.0 4 22.5 44.5 22.0 5 23.0 (ii) Calculate the temperature rise when 2 and when 5 pieces of magnesium ribbon are added. Record these values in Table 1.1. [1] (b) Describe one observation the student makes that shows that the magnesium has reacted completely with the hydrochloric acid. ................................................................................................................................................... ............................................................................................................................................. [1] (c) Describe the relationship between the number of pieces of magnesium ribbon and the temperature rise of the reaction. ................................................................................................................................................... ............................................................................................................................................. [1] (d) State one variable that must be controlled during this reaction. ............................................................................................................................................. [1] (e) Suggest one improvement that would increase the accuracy of the experiment. ............................................................................................................................................. [1] (f) A student repeats the experiment with 10 pieces of magnesium ribbon and 25 cm3 of hydrochloric acid. The acid is still in excess. Suggest the temperature rise for this reaction. ............................................................................................................................................. [1] (g) When 15 pieces of magnesium are added the magnesium is in excess. The student measures the temperature rise when 15 pieces of magnesium are added and again when 20 pieces of magnesium are added. Suggest the relationship between these two temperature rises. ............................................................................................................................................. [1] (h) Procedure The student then: • measures 10 cm3 of hydrochloric acid and pours it into a boiling tube • adds 5 drops of universal indicator (full range indicator) • records the colour of the solution in the boiling tube • adds small pieces of magnesium until no more will react • records the changes to the colour of the solution in the boiling tube. Universal indicator turns red in hydrochloric acid The Universal Indicator turns orange then yellow then green Fig. 1.2 The student’s record of colour changes is shown in Fig. 1.2. (i) Describe what happens to the hydrochloric acid as it reacts with magnesium. ..................................................................................................................................... [1] (ii) Describe the test that identifies the gas given off as hydrogen. test .................................................................................................................................... observation ......................................................................................................................... [1] (i) One way to investigate the rate of this reaction is to collect the gas and measure the volume of gas collected every minute. Draw a labelled diagram of the assembled apparatus used for this experiment. [2] [Total: 13]

Mark scheme: 1(a) 33.0 ; 49.5 ; 2 1(a)(ii) 11.(0) and 26.5 1 1(b) 1 from: magnesium disappears / is dissolved / no bubbles / temperature stops rising / changing / temperature remains constant;; 1 1(c) as (number of) magnesium (pieces) increases so temperature rise / change increases ; 1 1(d) concentration of acid / volume of acid ; 1 1(e) pipette / burette / insulate boiling tube ; 1 1(f) 50–55 ; INDEPENDENT 1 1(g) same 1 1(h)(i) it is used up / its pH increases / it gets less acidic / weaker / it is neutralised ; 1 1(h)(ii) lighted splint and pops ; 1 1(i) flask and delivery tube ; syringe / upturned measuring cylinder / burette in water ; 2

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2 A student investigates the magnification produced by a converging lens. Fig. 2.1 shows the apparatus used. illuminated u object screen lens Fig. 2.1 (a) • The illuminated object is a triangular hole in a piece of card, as shown in Fig. 2.2. ho Fig. 2.2 • The student measures and records the height ho of the triangular-shaped hole of the illuminated object. The measurement is shown in Fig. 2.3. ho = 1.5 cm Fig. 2.3 The student then: • sets the distance u (shown on Fig. 2.1) between the illuminated object and the lens to 25.0 cm • moves the screen until a sharp image of the triangle is seen on the screen, as shown in Fig. 2.4 on page 6. image hi Fig. 2.4 (i) Measure the height hi of the image and record it in Table 2.1. Table 2.1 u / cm hi / cm J 25.0 30.0 2.7 0.56 35.0 2.0 0.75 40.0 1.5 1.00 45.0 1.2 1.25 [1] (ii) The student repeats the procedure for values of u = 30.0 cm, 35.0 cm, 40.0 cm and 45.0 cm. The results are shown in Table 2.1. Calculate J for u = 25.0 cm. Use the value of ho on page 5 and your measurement of hi from (i). Record the answer in Table 2.1. Use the equation: ho J = [1] hi (b) (i) Plot a graph of u (vertical axis) against J. You do not have to start your graph at the origin (0, 0). [3] (ii) Draw the line of best fit. [1] (c) Calculate the gradient G of your line drawn in (b)(ii). Show all working and indicate on your graph the points you use to calculate the gradient. G = .......................................................... [2] (d) State one precaution that you would take in this experiment to obtain accurate readings. ................................................................................................................................................... ............................................................................................................................................. [1] (e) The student notices that one difficulty in measuring the height of the image is that the ruler used and the hand holding it cast a shadow over the image. Suggest an improvement to the apparatus or the arrangement of the apparatus to overcome this difficulty. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 10]

Mark scheme: 2(a)(i) hI = 4.7 (cm) 1 2(a)(ii) J = 0.32 1 Question Answer Marks 2(b)(i) graph: axes labelled correct orientation, with quantity and unit 1 appropriate linear scales and plots occupying at least ½ grid 1 plots all correct to ½ small square on scales which are linear for plotted points section 1 2(b)(ii) Well-judged and ruler drawn straight line 1 2(c) G in range 20.0 to 24.0 ONLY 1 triangle method seen on graph occupying at least half line 1 2(d) any one from: repeat and average ; use of a darkened room / brighter lamp ; mark position of centre of lens on holder ; place metre rule on bench / clamp in position ; ensure object and (centre of) lens are same height (from the bench) ; All / object and lens and screen perpendicular to bench ; move screen slowly / back and forth (to obtain best image) 1 2(e) any suitable improvement: use translucent screen / see-through paper and view from behind ; fix ruler / grid to screen 1

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3 A student investigates the stretching of two identical springs. Fig. 3.1 shows the set-up of the apparatus used to investigate one of the springs. clamp clamp boss spring l 0 stand metre rule bench Fig. 3.1 cm 10.0 spring l 0 11.0 12.0 Fig. 3.2 (a) Fig. 3.2 shows the unstretched spring. Take measurements from Fig. 3.2 to determine the original length l0. Record your value in Table 3.1 for L = 0.0 N and on the answer line. l0 = ................................................... cm [1] The student: • hangs a 1.0 N load on the spring • records the new length l of the spring in centimetres to the nearest millimetre • repeats the procedure using loads of 2.0 N and 3.0 N. The measurements are shown in Table 3.1. (b) Describe one precaution which should be taken to ensure that the readings of length are as accurate as possible. ................................................................................................................................................... ...............................................................................................................................................[1] (c) Calculate the extension x for each load. Record your values in the third column of Table 3.1. Use the equation: x = l – l0 Table 3.1 L / N l / cm x / cm 0.0 1.0 4.5 2.0 8.0 3.0 11.6 [2] (d) Predict the extension for a load L of 5.0 N. Use data from Table 3.1. x = ................................................... cm [1] (e) Calculate the spring constant k1 of the spring when L = 3.0 N. Use the equation: L k1 = x Give your answer to a suitable number of significant figures. k1 = ............................................... N / cm [2] (f) The student removes the load from the spring and attaches a second identical spring to the bottom of the first. Fig. 3.3 shows the arrangement of the two springs. Fig. 3.3 The student determines the extension x2 of the combined springs for a load L of 3.0 N. The value is shown in Fig. 3.4. x2 = 25.0 cm. Fig. 3.4 (i) Calculate the spring constant k2 of the combined springs. Use the equation: L k2 = x2 k2 = ............................................... N / cm [1] (ii) The student suggests that the spring constant k2 of the combined springs is equal to half of the spring constant k1 of just one of the springs. Explain whether the calculated values of k1 and k2 support this suggestion within the limits of experimental error. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1]

Mark scheme: 3(a) 3(b) use a set square / ruler to line up with scale / use a fiducial aid / perpendicular viewing of ruler ; 1 Question Answer Marks 3(c) all values correct (2.9, 6.4, 10.0) 1 consistent to 1dp INDEPENDENT 1 3(d) value within the range 16 to 18 (cm) INDEPENDENT 1 3(e) 0.30 1 2 or 3 significant figures INDEPENDENT 1 3(f)(i) 0.12 (N / cm) ONLY 1 3(f)(ii) Expect (implication of) NO matching justification e.g. difference is (too) large 1 3(g) any one from: repeat and take an average ; construct a graph ; calculate (a spring constant from) the gradient of the graph line ; use a greater range of / more loads / use another load ; 1

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4 Lemon juice and lime juice both contain acid. Acids are neutralised by alkalis. Plan an experiment to compare the amount of acid in lemon juice and in lime juice. You may use any common laboratory apparatus, aqueous sodium hydroxide, any test reagents and a lemon and a lime. Your plan should include: • a brief description of the method including the apparatus you would use • safety precautions AND explain why these are needed • the variables to control • the measurements you will make • an explanation of how you would use your results to reach a conclusion. 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Mark scheme: 4 At least one mark must be awarded from each section. The remaining three marks can be awarded from any section. apparatus (can be scored from a labelled diagram) juice in container (test-tube / beaker / conical flask / evaporating basin) ; use of (dropping) pipette / burette; measuring cylinder ; method add indicator ; add NaOH (slowly) ; until indicator (just) changes colour ; repeat (with same juice) / repeat with the other juice ; safety: goggles / gloves as substance(s) corrosive control: same amount of juice / indicator ; measurements measure amount / volume of juice ; measure volume sodium hydroxide / take burette readings at start and end OR measure amount of NaOH / number of drops needed to change colour of indicator OR measure volume of juice at start and juice + NaOH at end ; processing and use of results larger volume / more drops of NaOH means larger amount of acid ; volume NaOH used = amount NaOH initially – amount NaOH left at end/difference between burette readings OR volume NaOH used = amount NaOH and juice at end – amount of juice ; 7

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