Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2019 Oct/Nov Paper 6 · Variant 1

1 A student investigates an enzyme controlled reaction. Catalase is an enzyme that is found inside living cells, such as those found in beans. It catalyses the breakdown of hydrogen peroxide. Oxygen gas is released during the reaction and a foam is produced. (a) Procedure • A student places some liquidised beans in a test-tube. • He adds some hydrogen peroxide solution and starts a stopclock. • He measures the time it takes for the foam produced to reach the top of the test-tube. • He empties the test-tube and rinses it with distilled water. • He repeats the procedure two more times. • His stopclock readings are shown in Fig. 1.1. min sec min sec min sec trial 1 trial 2 trial 3 Fig. 1.1 (i) Read the stopclocks in Fig. 1.1. Record in Table 1.1 the time in seconds for each trial. [2] (ii) Calculate the average time taken. Record this value in Table 1.1. Table 1.1 time taken for foam to reach the top of the test-tube / s trial 1 trial 2 trial 3 average [1] (iii) State one variable that must be kept constant in this experiment. ..................................................................................................................................... [1] (b) Fig. 1.2 shows a test-tube containing liquidised beans and hydrogen peroxide solution. Draw on Fig. 1.2 suitable apparatus to collect the oxygen gas produced. foam liquidised beans and hydrogen peroxide solution Fig. 1.2 [1] (c) Describe the test to identify oxygen gas. Include the observation for a positive result. test ............................................................................................................................................ observation for a positive result ................................................................................................ [2] (d) The student tests the liquidised beans for their nutrient content. He uses Benedict’s solution and biuret solution. The liquidised beans test positive with both solutions. Use this information to complete Table 1.2. Table 1.2 colour observed after adding test solution nutrient content of beans test solution Benedict’s solution biuret solution [4] (e) Describe how the student could test a liquid for the presence of fat. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] [Total: 13]

Mark scheme: 1(a)(i) 90 85 95 ; ; 2 1(a)(ii) 90 ; 1 1(a)(iii) any one of: Temperature / volume / amount of beans / same size test-tube / amount / volume / concentration of hydrogen peroxide AVP ; 1 1(b) gas tight and works and safe ; 1 1(c) glowing splint ; relights ; 2 1(d) yellow / green / orange / red ; reducing sugar ; purple / lilac ; protein ; 4 1(e) (add) ethanol (to dissolve the fat) and (pour solution into) water ; white emulsion ; 2

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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. A student suggests that the rate of photosynthesis in aquatic plants is affected by the colour of light that the plant receives. Plan an investigation to see which colour of light produces the greatest rate of photosynthesis in an aquatic plant. You are given several samples of the same aquatic plant and sources of red light, blue light and green light. You may also use any other common laboratory apparatus. Do not carry out this investigation. Include in your answer: • what you would do, including the apparatus you would use • what you would measure • what you would control • how you would use your results to draw a conclusion • a labelled diagram, if you wish. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7] [Total: 7]

Mark scheme: 2 apparatus pond weed in container of water ; method use of one light source on its own ; all three light sources used separately ; repeats i.e. more than one full set of results ; measure number of bubbles / volume of gas produced ; in a set time ; or time ; collect set volume of gas / number of bubbles ; control same plant / same amount / same species of plant ; same distance of lamp from plant / same light intensity ; same temperature ; same water source ; same carbon dioxide concentration ; no contamination from other light sources ; conclusion greatest volume of gas / number of bubbles or shorter time to collect is colour / light that gives greatest rate ORA ; Max 7 7

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3 A student investigates the effect of the surface area of a solid on the rate of the reaction. She reacts marble chips (calcium carbonate) with hydrochloric acid. This reaction produces a gas. (a) Procedure • She sets up the apparatus as shown in Fig. 3.1. bung delivery tube test-tube for marble chips limewater and acid Fig. 3.1 • She removes the bung from the empty test-tube. • She places 10 marble chips of approximately the same size in the empty test-tube. • She adds 5 cm3 hydrochloric acid to the marble chips and replaces the bung. • She immediately starts the stopclock. • She stops the stopclock when the limewater turns milky. • She records in Table 3.1 this time t to the nearest second. She repeats the procedure using 20, 30 and 40 marble chips. (i) Fig. 3.2 shows the stopclock reading for 20 marble chips. Read and record in Table 3.1 this time to the nearest second. min sec 20 marble chips Fig. 3.2 Table 3.1 1 rate time t t number of marble chips / s / 1s 10 60 0.017 20 30 21 0.048 40 11 0.091 [1] (ii) State the name of the gas which turns limewater milky. ..................................................................................................................................... [1] (iii) Describe what the student needs to do to the apparatus and used chemicals between each experiment. apparatus ........................................................................................................................... ........................................................................................................................................... used chemicals .................................................................................................................. ........................................................................................................................................... [2] 1(b) (i) Calculate the rate for 20 marble chips. t Record in Table 3.1 this value to two significant figures. [2] (ii) The surface area of the marble chips increases as the number of chips increases. Use the information in Table 3.1 to state the relationship between the rate of the reaction and the total surface area of the marble chips. ........................................................................................................................................... ..................................................................................................................................... [1] (c) (i) State one variable which is kept constant in this experiment. ..................................................................................................................................... [1] (ii) Suggest one reason why varying the number of marble chips is not a fair way of changing the total surface area. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Suggest one other major source of inaccuracy in the procedure for this experiment. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 10]

Mark scheme: 3(a)(i) 29 ; 1 3(a)(ii) carbon dioxide ; 1 3(a)(iii) wash out apparatus ; discard chemicals ; 2 3(b)(i) 0.034(482758) any number of sf greater than 2 ; 0.034 i.e. 2sf ; 2 3(b)(ii) the greater the surface area the greater the rate ; 1 3(c)(i) any one of: volume / amount of acid / concentration of acid / temperature / volume / amount of limewater ; 1 3(c)(ii) chips not exactly the same size ; 1 3(c)(iii) timing to the same milkiness (opaqueness of ppt.) in limewater ; 1

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4 A student investigates the properties of compound H and identifies the ions in H. (a) (i) He places 25 cm3 of distilled water in a large test-tube. He measures the temperature T1 of this water. Fig. 4.1 shows the thermometer reading of T1. °C 30 20 10 T1 Fig. 4.1 Read and record T1 to the nearest 0.5 °C. T1 = .....................................................°C [1] (ii) Procedure • He adds compound H to the water and stirs. • He measures the highest or lowest temperature T2 reached by the mixture. • He keeps this mixture for use in (b) and (c). • He describes the appearance of the mixture as shown in Fig. 4.2. colourless liquid appearance of mixture................................................................ Fig. 4.2 Fig. 4.3 shows the thermometer reading of T2. °C 30 20 10 T2 Fig. 4.3 Read and record T2 to the nearest 0.5 °C. T2 = .....................................................°C [1] (iii) Calculate the temperature change ΔT when H is added to water in (a)(ii). Include a plus (+) or minus (–) sign as appropriate. ΔT = .....................................................°C [1] (iv) State two conclusions about what happens when H is mixed with water. Use the observation in Fig. 4.2 and the calculation in (a)(iii). conclusion 1 ....................................................................................................................... conclusion 2 ....................................................................................................................... [2] (b) (i) He places some of the mixture from (a)(ii) in a test-tube and adds an equal volume of dilute nitric acid. He then adds a few drops of barium nitrate solution. His observations are shown in Fig. 4.4. observations remains a colourless solution with nitric acid................................................................... remains a colourless solution with barium nitrate................................................................... Fig. 4.4 State the conclusions that the student can make from the observations in Fig. 4.4 about the anions present or not present in H. ........................................................................................................................................... ..................................................................................................................................... [2] (ii) He places some of the mixture from (a)(ii) in a test-tube and adds an equal volume of dilute nitric acid. Then he adds a few drops of silver nitrate solution. His observations are shown in Fig. 4.5. observations remains a colourless solution with nitric acid................................................................... white ppt. with silver nitrate................................................................... Fig. 4.5 State the conclusions that the student can make from the observations in Fig. 4.5 about the anions present or not present in H. ........................................................................................................................................... ..................................................................................................................................... [1] (c) The student tests the mixture from (a)(ii) for the presence of a cation. He concludes that the cation is the ammonium ion. Complete Table 4.1 to show the tests and observations that confirm this conclusion. Table 4.1 test observation ............................................. remains colourless and no ppt. ............................................. warm and place damp litmus ............................................. papers at the mouth of the test-tube ............................................. [2] [Total: 10]

Mark scheme: 4(a)(i) 23.5 ; 1 4(a)(ii) 18.0 / 18 ; 1 4(a)(iii) –5.5 ; 1 4(a)(iv) H is soluble in water / H dissolves ; absorbs heat / endothermic ; 2 4(b)(i) not carbonate ; not a sulfate ; 2 4(b)(ii) chloride / Cl – ; 1 4(c) (add aqueous) sodium hydroxide ; (red litmus to) blue ; 2

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5 A student calculates an approximate value for the density of modelling clay. (a) She moulds a piece of modelling clay into a block, similar to the one shown in Fig. 5.1. h l w Fig. 5.1 (i) Measure and record the length l, width w and height h of the block in Fig. 5.1 to the nearest 0.1 cm. l = ..........................................................cm w = ..........................................................cm h = ..........................................................cm [2] (ii) Calculate the volume V of the block. Use the equation shown. V = l × w × h V = ...................................................cm3 [1] (b) (i) State one reason why the value for the volume is not accurate. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Suggest an alternative method of measuring the volume of the block that would give the student a more accurate value. ........................................................................................................................................... ..................................................................................................................................... [1] (c) Procedure • The student attaches a mass to a metre rule. • She fixes the position of the mass with its centre over the 15.0 cm mark. • She does not move this mass. • She places a pivot under the 50.0 cm mark, as shown in Fig. 5.2. mass secured to rule block of x modelling clay 0 100 15.0 cm mark 50.0 cm mark Fig. 5.2 • She places the block of modelling clay on the metre rule. • She adjusts the position of the block of modelling clay until the rule is just balanced. Fig. 5.3 shows the position of the centre of the block when the rule is balanced. 66 67 68 69 70 position of centre of block at balance Fig. 5.3 (i) Determine the distance x from the centre of the block to the 50.0 cm mark on the rule. Show your working. x = .................................................... cm [2] (ii) Calculate the mass m of the block of modelling clay. Use the equation shown. 1750 m = x m = .......................................................g [1] (d) (i) State one reason why the value for the mass that you have calculated in (c)(ii) may not be accurate. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Use your answers to (a)(ii) and (c)(ii) to calculate the density d of the modelling clay. Use the equation shown. m d = V d = ...............................................g / cm3 [1] [Total: 10]

Mark scheme: 5(a)(i) w = 3.4 h = 2.0 all to nearest millimetre 2 5(a)(ii) V = 36(.04) (cm3) ; 1 5(b)(i) block is not a regular shape / corresponding sides unequal / difficult to measure because sides not straight / rule only reads to the nearest mm ; 1 5(b)(ii) use a measuring cylinder / displacement can / displacement of water ; 1 5(c)(i) 68.6 ; x = 18.6 ; 2 5(c)(ii) m correct and rounded correctly, 1750 ÷ (c)(i) ; 1 5(d)(i) difficult to obtain an exact balance / centre of block difficult to place over mark ; 1 5(d)(ii) calculation correct, (c)(ii) ÷ (a)(ii) ; 1

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6 A student investigates how the resistance of a wire depends upon its length. He sets up the circuit shown in Fig. 6.1. V resistance wire C A B l metre rule A power source Fig. 6.1 (a) Procedure • He closes the switch. • He places the sliding contact C on the wire so that the length of wire l = 10.0 cm. • He measures, and records in Table 6.1, the current I in the wire. • He measures, and records in Table 6.1, the potential difference V across the wire. • He opens the switch. Fig. 6.2 shows the voltmeter reading for l = 10.0 cm. 0.5 0.4 0.6 0.3 0.7 V 0.2 0.8 0.1 0.9 0 1.0 Fig. 6.2 (i) Record the value of V in Table 6.1. Table 6.1 resistance R length l current I potential difference V / cm / A / V / .................. 10.0 0.36 20.0 0.36 0.62 1.7 30.0 0.36 0.91 2.5 40.0 0.36 1.20 3.3 50.0 0.36 4.2 [1] (ii) Complete the column heading in Table 6.1 by inserting the missing unit for resistance. [1] (iii) Calculate the resistance of the 10.0 cm length of the wire. Use the equation shown. V R = I Record your answer in Table 6.1. [1] (b) He repeats the procedure in (a) for values of length l = 20.0 cm, 30.0 cm, 40.0 cm and 50.0 cm. From the information given in Table 6.1, calculate the missing value of potential difference V when l = 50.0 cm. Record this value in Table 6.1. [1] (c) (i) Plot a graph of R (vertical axis) against l . Start your axes from the origin (0, 0). [3] (ii) Draw the best-fit straight line on the graph in (c)(i). [1] (d) (i) Another student states that the resistance R of the wire is directly proportional to the length l . State whether your graph agrees with this statement. Justify your answer by referring to the graph you have drawn. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) State how the student could improve the investigation so that she can be more confident about the conclusion in (d)(i). ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 10]

Mark scheme: 6(a)(i) 0.31 ; 1 6(a)(ii) Ω ; 1 6(a)(iii) 0.9 / 0.86 (Ω) ; 1 6(b) 1.51 (V) ; 1 6(c)(i) axes labelled with units correct orientation ; suitable choice of scales (⩾ half the grid used) ; 4 plots correct to half a small square ; 3 6(c)(ii) good best-fit line judgement ; 1 6(d)(i) (expect yes) (straight) line through the origin ; 1 6(d)(ii) more values of l / repeats ; 1

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