Cambridge IGCSE Science - Combined 0653 — 2022 May/June Paper 5 · Variant 1

1 You are going to investigate the effect of ethanol on cell membranes. Beetroot cells contain a red colour that comes out of the cells when the cell membranes break. Ethanol can break down the cell membranes. You are provided with some ethanol, distilled water and five pieces of beetroot of equal size. Procedure Step 1 Label five boiling tubes (large test-tubes) A, B, C, D and E. Step 2 Use syringes to add 8 cm3 of ethanol and 2 cm3 of distilled water to boiling tube A. Step 3 Repeat Step 2 by adding ethanol and distilled water to boiling tubes B, C, D and E using the volumes shown in Table 1.1. Table 1.1 boiling tube volume of ethanol volume of distilled water / cm3 / cm3 A 8 2 B 6 4 C 4 6 D 2 8 E 0 10 Step 4 On a white tile, cut one piece of beetroot into 10 thin discs as shown in Fig. 1.1. beetroot disc Fig. 1.1 Step 5 Put the 10 discs of cut beetroot into boiling tube A. Step 6 Repeat Step 4 and Step 5 for boiling tubes B, C, D and E. Step 7 Start the stop-watch and leave for 10 minutes. While waiting you can start question 2. Step 8 After 10 minutes, gently swirl each boiling tube to mix the contents. (a) Place your five boiling tubes in colour order, from darkest red to lightest red. Record in Table 1.2 the order of your boiling tubes. Table 1.2 colour boiling tube darkest red ............................ ............................ ............................ ............................ lightest red ............................ [3] (b) State the relationship between concentration of ethanol and darkness of colour in this experiment. ................................................................................................................................................... ............................................................................................................................................. [1] (c) State why different volumes of water are used in this experiment. ................................................................................................................................................... ............................................................................................................................................. [1] (d) Describe one source of error in the procedure. ................................................................................................................................................... ............................................................................................................................................. [1] (e) Identify one safety hazard in the procedure and suggest a way to reduce the risk. safety hazard ............................................................................................................................ ................................................................................................................................................... way to reduce risk ..................................................................................................................... ................................................................................................................................................... [1] [Total: 7]

Mark scheme: 1(a) all five values recorded ; A higher than E ; all values in correct order ; 3 1(b) the higher the (concentration of) ethanol the higher the colour score ORA ; 1 1(c) so that total / final volume is constant; 1 1(d) not all put into boiling tubes at the same time / in the ethanol for different times; 1 1(e) use of a knife / cutting beetroot (into discs) AND cutting away from body / keep away from hands/fingers / use of a flat solid surface; OR ethanol flammable AND no naked flames; 1

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2 Photosynthesis takes place in aquatic plants (plants that live in water). Photosynthesis produces bubbles of oxygen gas. The greater the rate of photosynthesis, the faster the oxygen is produced. Figure 2.1 shows apparatus used to investigate the effect of light intensity (amount of light) on the rate of photosynthesis. oxygen gas test-tube lamp funnel support block green aquatic plant Fig. 2.1 Plan an investigation to find the relationship between light intensity and the rate of photosynthesis. You are provided with the apparatus in Fig. 2.1. You may also use any other common laboratory apparatus. You are not required to do this investigation. In your plan, include: • the additional apparatus needed • a brief description of the method and an explanation of any safety precautions you will take • what you will measure • which variables you will keep constant • how you will process your results to draw a conclusion. You may include a table that can be used to record the results if you wish. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 2 One marking point from each section and any other two marks 1. Apparatus timer / stopwatch / stop-clock ; ruler / light meter / method of varying light intensity (e.g. variable resistor / light filters) ; 2. Method and safety use blackout ; put lamp at different distances ; do at least five different distances ; care with hot lamp because of burns to hand / electricity and water because of shock / dark glasses to protect from bright light ; 3. Measurements same time and count number of bubbles / measure volume of gas OR same number of bubbles / volume and measure length of time ; measure distance to lamp / measure light intensity / suggests appropriate measurement of distance / light intensity ; 4. Constant variables same lamp / same plant / same amount / type / number of plant(s) ; same time / same volume / same number of bubbles (depends on method) ; same temperature (of water) ; 5. Processing results processes to give rate e.g. divide number of bubbles / volume of gas by time / state units for rate e.g. bubbles or volume per specified time ; do repeats under same conditions and take an average / exclude anomalous results / check results are similar ; plot volume / amount / number of bubbles / time / rate against distance of lamp / light intensity ; 7

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3 You are going to investigate some reactions of dilute sulfuric acid. (a) Procedure Step 1 Add approximately 2 cm depth of dilute sulfuric acid to a test-tube. Step 2 Add approximately 1 cm depth of dilute nitric acid followed by approximately 1 cm depth of aqueous barium nitrate to the test-tube. (i) Describe your observations. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Name the negative ion (anion) present in dilute sulfuric acid. ..................................................................................................................................... [1] (b) Procedure Step 1 Add approximately 2 cm depth of dilute sulfuric acid to a boiling tube (large test-tube). Step 2 Add a small spatula load of solid sodium hydrogencarbonate to the boiling tube. Describe your observations. ................................................................................................................................................... ............................................................................................................................................. [2] (c) Procedure Step 1 Add approximately 5 cm depth of dilute sulfuric acid to a clean test-tube. Step 2 Add one piece of magnesium to the test-tube. The mixture fizzes. (i) Test the gas made with a lighted splint. Name the gas made. observation with lighted splint ........................................................................................... name of gas ...................................................................................................................... [1] (ii) Procedure Step 1 Add approximately 5 cm depth of dilute sulfuric acid to a clean boiling tube. Step 2 Add one piece of magnesium into the dilute sulfuric acid and immediately start the stop-watch. Step 3 Stop the stop-watch when the mixture stops fizzing. Record to the nearest second this time in seconds. time = ...................................................... s [2] (d) Procedure Step 1 Add approximately 5 cm depth of dilute sulfuric acid to a clean boiling tube. Step 2 Measure the temperature of the dilute sulfuric acid. (i) Record this temperature in Table 3.1. [1] Table 3.1 temperature of dilute sulfuric acid / °C temperature of reaction mixture / °C temperature increase / °C (ii) Step 3 Add approximately 5 cm depth of aqueous sodium hydroxide to the acid in the boiling tube. Step 4 Stir the mixture with the thermometer for approximately 20 seconds. Step 5 Measure the temperature of the reaction mixture. Record this temperature in Table 3.1. [1] (iii) Calculate the temperature increase. Record your answer in Table 3.1. [1] (iv) The temperature increase is not as large as expected. This is because some thermal energy (heat) is transferred into the air. Suggest a change in the apparatus or an addition to the apparatus that reduces this loss in thermal energy (heat). ........................................................................................................................................... ..................................................................................................................................... [1] (v) Suggest why the reaction mixture is stirred before its temperature is recorded. ........................................................................................................................................... ..................................................................................................................................... [1] (vi) Suggest why it is better to repeat the experiment and calculate the average temperature increase. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 13]

Mark scheme: 3(a)(i) white precipitate ; 1 3(a)(ii) sulfate ; 1 3(b) effervescence / fizzes / bubbles ; colourless solution ; 2 3(c)(i) (squeaky) pop AND hydrogen ; 1 3(c)(ii) greater than 15 seconds ; time converted into seconds ; 2 3(d)(i) temperature recorded ; 1 3(d)(ii) temperature recorded that is higher than in (d)(i) ; 1 3(d)(iii) correct temperature increase calculated ; 1 3(d)(iv) lid / insulation ; 1 3(d)(v) to ensure even temperature throughout ; 1 3(d)(vi) idea that takes into account variation in results / temperature / idea of temperature varying / temperatures may be different (each time) ; 1

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4 You are going to use a spring to determine the mass of an unknown object O. The apparatus shown in Fig. 4.1 has been set up for you. cm metre rule clamp stand spring suspended from clamp lower ring Fig. 4.1 (a) Record the reading r0 on the metre rule at the bottom of the spring. (Do not include the lower ring.) Give your answer in centimetres to the nearest 0.1 cm. r0 = ................................................... cm [1] (b) (i) Procedure Step 1 Add a mass m = 100 g to the spring. Step 2 Record in Table 4.1 the reading rl on the metre rule at the bottom of the spring. Step 3 Remove the mass from the spring. [1] Table 4.1 m rl e / g / cm / cm 100 200 300 400 500 (ii) Describe how you avoid line-of-sight (parallax) errors when taking the reading at the bottom of the spring. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Repeat the procedure in (b)(i) with values of mass m = 200 g, 300 g, 400 g and 500 g. [2] (iv) Calculate the extension e of the spring for each mass m added to the spring. Use the equation shown. e = rl – r0 Record your values in Table 4.1. [1]

Mark scheme: 4(a) suitable value recorded to nearest 0.1 cm ; 1 4(b)(i) value recorded > (a) ; 1 4(b)(ii) idea that the metre rule is read perpendicular to the scale / take the reading perpendicular (to bottom of the spring) / use of fiducial aid ; 1 4(b)(iii) all values recorded ; values increasing with increasing mass ; 2 Question Answer Marks 4(b)(iv) extensions correctly calculated ; 1 4(c)(i) axes correct, labelled and with units, correct way round ; linear scale so that plotted points cover at least ½ grid in each direction ; points plotted correctly  1 / 2 small square ; 3 4(c)(ii) good best-fit line judgement ; 1 4(d)(i) correct calculation of extension ; 1 4(d)(ii) correct value of mass found from candidate’s graph ; evidence of working shown on the graph ; 2

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