Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2019 Oct/Nov Paper 6 · Variant 2

1 A student investigates the nutrient content of yogurt and rice water. He uses Benedict’s solution, biuret solution and iodine solution. The yogurt gives a positive result with Benedict’s solution and biuret solution. The rice water gives a positive result with iodine solution. All other test results are negative. (a) Complete Table 1.1 to show the student’s observations of the final colours for each of the test-tubes. A colour should be recorded in every box. Table 1.1 observation with observation with observation with food sample Benedict’s solution biuret solution iodine solution yogurt rice water [4] (b) Use the results to state the nutrients present in each food sample. yogurt contains ......................................................................................................................... rice water contains .................................................................................................................... [3] (c) State which of these tests requires the use of heat. ............................................................................................................................................. [1] (d) A student wants to compare concentrations of the nutrient tested for with Benedict’s solution. State one variable that would need to be kept the same. ............................................................................................................................................. [1] (e) A student carries out this investigation but also tests samples of protein, reducing sugar and starch with the three test solutions. Explain how this improves the investigation. ................................................................................................................................................... ............................................................................................................................................. [1] (f) (i) A student tests a liquid for the presence of fats by adding two substances. He gets a positive result. Name the two substances added in the test. .................................................................. and .................................................................. State his observation. ........................................................................................................................................... [2] (ii) Explain why the test in (f)(i) is not suitable for testing for the presence of fat in milk. ..................................................................................................................................... [1] [Total: 13]

Mark scheme: 1(a) Yellow / green / orange / red ; Purple / lilac ; orange / brown / yellow Blue and blue; Blue-black; 4 1(b) (yogurt) protein; reducing sugar ; (rice water:) starch ; 3 1(c) Benedict's / (reducing) sugar ; 1 1(d) any one from: same volume / amount of food samples ; same volume / amount / concentration / batch of Benedict’s ; (leave for) same time ; same temperature ; 1 1(e) check reagents working / (confirm) colours for a positive result ; 1 1(f)(i) ethanol / alcohol and water ; white emulsion ; 2 1(f)(ii) cannot see result AW ; 1

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2 Fig. 2.1 shows a photograph of the cut surface of half a tomato. A B Fig. 2.1 (a) In the box, make an enlarged detailed pencil drawing of Fig. 2.1. [4] (b) (i) Draw a straight line between points A and B on Fig. 2.1. This is the actual width of the tomato. Measure and record this width in millimetres to the nearest millimetre. actual width .................................................. mm [1] (ii) Draw a line to show this width on your drawing. Measure and record the length of this line in millimetres to the nearest millimetre. width on drawing .................................................. mm [1] (iii) Use your measurements in (b)(i) and (b)(ii) to calculate the magnification m of your drawing. Use the equation shown. width on drawing m = actual width m = ......................................................... [1] [Total: 7]

Mark scheme: 2(a) clear and continuous outline ; larger than original ; central detail ; seeds visible ; 4 2(b)(i) 42 ; 1 2(b)(ii) line drawn and correct measurement ; 1 2(b)(iii) correct calculation ; 1

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3 A student investigates the reaction between zinc and aqueous copper sulfate. (a) She records the colours of the zinc and the aqueous copper sulfate as shown in Fig. 3.1. grey zinc…………………………………… blue aqueous copper sulfate……………… Fig. 3.1 She measures the temperature of the aqueous copper sulfate and records in Table 3.1 the value to the nearest 0.5 °C for time = 0. Table 3.1 time temperature / s / °C 0 20.0 30 39.0 60 41.0 90 39.5 120 38.5 150 37.5 180 210 36.0 240 35.5 270 300 34.0 • She places the zinc in a plastic cup. • She adds 20 cm3 aqueous copper sulfate to the zinc and starts the stopclock. • She stirs the mixture continuously. • She measures the temperature of the mixture every 30 seconds for 300 seconds. • She records in Table 3.1 these values to the nearest 0.5 °C. (i) Suggest a suitable piece of apparatus for measuring the volume of the aqueous copper sulfate. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Fig. 3.2 shows the thermometer readings at time = 180 s and time = 270 s. °C °C 40 40 30 30 time = 180 s time = 270 s Fig. 3.2 Read the thermometers in Fig. 3.2 and record in Table 3.1 the temperatures to the nearest 0.5 °C. [2] (iii) Suggest why it is not appropriate to record the temperatures in Fig. 3.2 to the nearest 0.25 °C. ........................................................................................................................................... ..................................................................................................................................... [1] (b) (i) Use the results in Table 3.1 to plot a graph of temperature against time. You do not need to start the temperature axis at zero. temperature / °C time / s [2] (ii) Draw the best-fit smooth curve. [1] (iii) Use the graph to find the maximum temperature reached during the experiment. Mark this temperature on your graph. maximum temperature .....................................................°C [2] (iv) The student records the colours of the solid and the liquid in the final mixture from (a). These are shown in Fig. 3.3. pinky brown solid……………………………… colourless liquid……………………………… Fig. 3.3 Use these observations and those in (a) to suggest the name of one of the products of this reaction. ..................................................................................................................................... [1] (v) Suggest the type of reaction that has taken place between zinc and aqueous copper sulfate. type of reaction ............................................................................................................ [1] (c) Suggest why the maximum temperature rise in the experiment should be more accurate when read from the graph than from the results in Table 3.1. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 12]

Mark scheme: 3(a)(i) measuring cylinder ; 1 3(a)(ii) (time = 180 s) 36.5 ; (time = 270 s) 35.0 ; 2 3(a)(iii) can only read to half a division / graduations are 1 °C ; 1 3(b)(i) linear scale and using at least half of grid ; at least 4 points correctly plotted to within ½ square within the first 180 seconds ; 2 3(b)(ii) best-fit smooth curve including one maximum ; 1 3(b)(iii) maximum temperature read correctly from graph ; maximum temperature marked on graph ; 2 3(b)(iv) copper / zinc sulfate ; 1 3(b)(v) displacement / exothermic / redox ; 1 3(c) best-fit line allows for a maximum between readings ; 1

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4 A student carries out tests on four aqueous solutions H, J, K and L to find out which is aqueous sodium hydroxide. The other three are aqueous solutions of the same acid but each has a different concentration. The student carries out further tests to identify the acid and place the three acid solutions in order of concentration. (a) He is supplied with the chemicals listed. aqueous barium nitrate aqueous copper sulfate aqueous silver nitrate He cannot use any other chemicals or testing materials. He carries out a test using one of the chemicals listed to find out which solution H, J, K or L is aqueous sodium hydroxide. State the chemical he uses to identify J as aqueous sodium hydroxide. Give the observation for this positive test. test ............................................................................................................................................. observation ................................................................................................................................ [1] (b) He carries out a controlled test on the three remaining acid solutions using marble chips. His observations are shown in Fig. 4.1. observations H produces a very fast stream of bubbles K produces a slow stream of bubbles L produces a fast stream of bubbles Fig. 4.1 (i) State two variables which must be controlled in this test. controlled variable 1 ........................................................................................................... controlled variable 2 ........................................................................................................... [2] (ii) Use the observations in Fig. 4.1 to state the order of concentration of the three acid solutions. Explain how you use the observations to find the order of the concentrations. most concentrated acid solution .................... .................... least concentrated acid solution .................... explanation ......................................................................................................................... ........................................................................................................................................... [2] (c) H, K and L are the same acid. Describe tests that the student uses to identify the acid. He uses only chemicals from the list in (a). Complete Table 4.1 with the chemicals used in the tests, and the observation for a positive test. Table 4.1 observation for a positive acid test test sulfuric hydrochloric [3] [Total: 8]

Mark scheme: 4(a) add copper sulfate and blue ppt ; 1 4(b)(i) Max two from: same number / amount / mass of chips ; same size / surface area of chips ; same temperature ; same volume / amount of acid / HKL / solution ; 2 4(b)(ii) H (most) L K (least) ; faster bubbling / more bubbles in H / more concentrated / slower bubbling / less bubbles in K / least concentrated; 2 4(c) white ppt ; white ppt ; barium nitrate and silver nitrate in correct position in table and no other reagents ; 3

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5 A student determines an approximate value for the specific heat capacity of glass. The specific heat capacity c of glass is the amount of thermal energy required to raise the temperature of 1 g of glass by 1 °C. (a) She uses a balance to find the mass m of an empty beaker P. Fig. 5.1 shows the reading on the balance. 47 . 81 g Fig. 5.1 Write down the mass of beaker P to the nearest gram. m = .......................................................g [1] (b) • She pours 100 cm3 of cold water into beaker P. • She measures and records the temperature θ1 of the cold water to the nearest 0.5 °C. Fig. 5.2 shows the thermometer reading. °C 20 10 Fig. 5.2 Write down the temperature θ1 of the cold water. θ1 = .....................................................°C [1] (c) • She pours 100 cm3 of hot water into a second beaker Q. • She places the thermometer into the hot water. • She measures and records the temperature θ2 of the hot water. 81.0 θ2 = ...........................................................°C • She pours the hot water from beaker Q into the cold water in beaker P. • She stirs the mixture. • She measures and records the temperature θ3 of the mixture. 48.0 θ3 = ...........................................................°C Explain why she stirs the mixture before recording its temperature. ................................................................................................................................................... ............................................................................................................................................. [1] (d) (i) Calculate the rise in temperature (θ3 – θ1) of the cold water. (θ3 – θ1) = .....................................................°C [1] (ii) Calculate the fall in temperature (θ2 – θ3) of the hot water. (θ2 – θ3) = .....................................................°C [1] (e) (i) Calculate the gain in thermal energy Ec of the cold water. Use the equation shown. Ec = 420 × (θ3 – θ1) Ec = ...................................................... J [1] (ii) Calculate the loss in thermal energy Eh of the hot water. Use the equation shown. Eh = 420 × (θ2 – θ3) Eh = ...................................................... J [1] (f) The difference between Eh and Ec is approximately equal to the thermal energy Eg gained by the glass beaker P. (i) Use your answers to (e)(i) and (e)(ii) to calculate the thermal energy gained by the glass. Use the equation shown. Eg = Eh − Ec Eg = ...................................................... J [1] (ii) Use your answers to (a), (d)(i) and (f)(i) to calculate the specific heat capacity c of glass. Use the equation shown. Eg = m × c × (θ3 – θ1) c = .............................................. J / g °C [2] (g) State two practical reasons why any value for the specific heat capacity of glass determined using this experiment is not accurate. reason 1 .................................................................................................................................... ................................................................................................................................................... reason 2 .................................................................................................................................... ................................................................................................................................................... [2] (h) Suggest one improvement to the apparatus that will give a more accurate value for the specific heat capacity of glass. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 13]

Mark scheme: 5(a) 48 ; 1 5(b) 18.5 ; 1 5(c) to ensure that all the water is at the same temperature ; 1 5(d)(i) 29.5 ; 1 5(d)(ii) 33 ; 1 5(e)(i) 12390 ; 1 5(e)(ii) 13860 ; 1 5(f)(i) 1470 ; 1 5(f)(ii) correct substitution / manipulation ; 1.04 (J / g °C) ; 2 5(g) Max two from: no lagging / lid / insulation ; heat / energy loss ; not all glass at same temperature ; water T not same as glass T water left in beaker after pouring ; volume of hot water approximate ; mass of beaker only to nearest g / rounding (the balance) reading ; transfer hot water too slowly ; misreading thermometer / misreading mass ; 2 5(h) insulate beaker(s) / use a lid / measure the volume with measuring cylinder ; 1

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6 A student investigates how the resistance of a wire depends upon its length. To calculate resistance he uses the equation shown. V R = I The apparatus available is listed. • power supply • ammeter • voltmeter • switch • several metres of resistance wires of different materials and thicknesses • metre rule • wire cutters • connecting leads • crocodile clips • beaker of cold water Plan an experiment to investigate how the resistance of the wire depends upon its length. You must select apparatus for your experiment from the list above. You may not use any other apparatus. You are not required to carry out this investigation. Include in your answer: • a diagram of the circuit you would use • how you would carry out the experiment • the key variables you would control • a table with column headings to show how you would present your results (you are not required to enter any readings in the table) • how you would use your readings to come to a conclusion. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 6 circuit diagram: cell in series with wire (and switch) ; voltmeter in parallel with the wire ; ammeter in series with the wire ; (cell) voltmeter, ammeter symbols correct ; method: take readings of V and I ; for three (or more lengths) / more lengths ; repeats – each length ; key variables: thickness / radius / diameter / cross sectional area of wire ; material / type of wire ; temperature of wire ; table: headings: l, V, I, R ; and all correct units present ; conclusion: compare readings of R and l (in the table) / plot graph of R vs l ; 7

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