Cambridge IGCSE Sciences - Co-ordinated (9-1) 0973 — 2022 May/June Paper 6 · Variant 2

1 A student investigates the movement of molecules through a cell membrane. The student uses dialysis (Visking) tubing that can act like a cell membrane. This tubing allows small molecules to pass through it but not large molecules. Procedure The student: Step 1 uses a syringe to put 2 cm3 of iodine solution into the dialysis tubing tied at one end Step 2 ties the open end with a knot to enclose the iodine solution inside and make a bag Step 3 rinses the outside of the bag with water Step 4 places the bag containing iodine solution into a beaker of starch solution as shown in Fig. 1.1 bag of iodine solution starch solution Fig. 1.1 Step 5 observes the colour in the bag and the colour in the beaker every minute for five minutes Step 6 records all colours in Table 1.1. Table 1.1 colour of solution time t / ............................... bag beaker 0 brown colourless 1 brown colourless 2 brown colourless 3 brown blue-black 4 brown blue-black 5 brown blue-black (a) Complete the heading in Table 1.1 by adding the unit for time. [1] (b) Iodine solution is a test for starch. Dialysis tubing allows small molecules to pass through it but not large molecules. Explain the observations for the colour of the solution inside the bag and the colour of the solution in the beaker after five minutes. Use the information provided and the results in Table 1.1. Include ideas about the size of molecules in your answer. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] (c) Suggest why a syringe is used to measure the 2 cm3 of iodine solution in Step 1 of the procedure instead of a measuring cylinder. ............................................................................................................................................. [1] (d) Suggest why the dialysis tubing is rinsed in Step 3 of the procedure. ............................................................................................................................................. [1] (e) At lower temperatures, molecules move more slowly. The student does the procedure at a lower temperature. Suggest how this affects the results. ............................................................................................................................................. [1] (f) (i) Starch is broken down into reducing sugar by the enzyme amylase. Describe a test to confirm the presence of reducing sugar. Include the colour observed for a positive result. test .................................................................................................................................... ........................................................................................................................................... observation ........................................................................................................................ [3] (ii) The enzyme amylase is a protein. Describe a test to confirm the presence of protein. Include the colour observed for a positive result. test .................................................................................................................................... ........................................................................................................................................... observation ........................................................................................................................ [2] [Total: 12]

Mark scheme: 1(a) minutes ; 1 1(b) 3 of: iodine turns blue-black in presence of starch ; starch molecules are large; iodine molecules are small ; bag doesn’t contain starch / starch cannot diffuse into the bag / starch cannot get though the membrane (because iodine brown / not blue-black) OR iodine (molecules move into) in beaker / starch / iodine (diffuses) out of the bag / iodine goes through the membrane (because iodine is blue-black) ; 3 1(c) more precise ; 1 1(d) avoid iodine on (outside) of the bag; 1 1(e) longer time / slower to turn blue-black / change colour / more negative / brown results ; 1 1(f)(i) Benedict’s; heat; red / orange / yellow / green; 3 1(f)(ii) biuret; lilac / purple / mauve / violet ; 2

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2 Fig. 2.1 shows a magnified section through part of a leaf. A cell C B Fig. 2.1 (a) In the box, make a large pencil drawing of only the cell labelled C and the 5 cells touching it. Do not draw any other cells. [3] (b) (i) The distance between the points A and B in Fig. 2.1 shows the thickness of the leaf. Draw a line between points A and B in Fig. 2.1. Measure the length of line AB in Fig. 2.1. Record this length in millimetres to the nearest millimetre. length of line AB in Fig. 2.1 = .................................................. mm [1] (ii) The thickness of the actual leaf at AB is 0.75 mm. Calculate the magnification m of the photograph. Use the equation shown. length of line AB in Fig. 2.1 m = thickness of the actual leaf at AB m = ......................................................... [1] (c) A teacher states that the thickness of the actual leaf measured between points A and B does not show the thickness of the whole leaf. Suggest why the teacher is correct. State how you can improve confidence in the measurement of the thickness of the whole leaf. suggestion ................................................................................................................................ ................................................................................................................................................... improvement ............................................................................................................................. ................................................................................................................................................... ................................................................................................................................................... [3] [Total: 8]

Mark scheme: 2(a) clear and continuous outline; size ⩾ ½ box ; 1 cell surrounded by 5 cells in correct shape ; 2(b)(i) 76 and line drawn; 1 2(b)(ii) 101 / 101.3 ; 1 2(c) bulge on photo / thickness of the leaf varies AW; measure at several / many places; calculate average / mean; 3

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3 A student investigates the rate of reaction when calcium carbonate reacts with dilute hydrochloric acid. (a) Procedure The student: Step 1 uses a measuring cylinder to place 25 cm3 of dilute hydrochloric acid into a conical flask Step 2 sets up the apparatus shown in Fig. 3.1 measuring cylinder dilute hydrochloric acid clamp water Fig. 3.1 Step 3 removes the stopper from the conical flask Step 4 adds the calcium carbonate to the conical flask, quickly replaces the stopper and immediately starts a stop-watch Step 5 measures the volume of gas in the measuring cylinder every 30 seconds for five minutes Step 6 records these volumes in Table 3.1. (i) Suggest another method of collecting and measuring the volume of gas. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) State the name of a piece of apparatus the student can use to measure the 25 cm3 of dilute hydrochloric acid in Step 1 more accurately. ..................................................................................................................................... [1] (iii) Suggest how the student knows when the reaction has finished. ........................................................................................................................................... ..................................................................................................................................... [1] (b) Fig. 3.2 shows part of the student’s notebook. Calcium carbonate is a white solid. When calcium carbonate is added to hydrochloric acid it fizzes. When the reaction has stopped there is a solid and a colourless liquid in the conical flask. Fig. 3.2 Suggest which reagent, calcium carbonate or dilute hydrochloric acid, is in excess. Give a reason for your answer. Use the notebook to help you answer the question. ................................................................................................................................................... ............................................................................................................................................. [1] (c) Fig. 3.3 shows the measuring cylinder at 60 seconds and 150 seconds. Record these volumes in Table 3.1. 20 20 gas 40 40 60 60 water 80 80 100 100 cm3 cm3 volume of gas at 60 seconds volume of gas at 150 seconds Fig. 3.3 Table 3.1 time / s volume of gas / cm3 0 0 30 10 60 90 40 120 44 150 180 41 210 50 240 51 270 51 300 51 [2] (d) (i) On the grid, plot a graph of volume of gas (vertical axis) against time. [3] (ii) Circle the anomalous point on the graph. [1] (iii) Draw the line of best-fit which shows how the volume of gas changes with time. [1] (e) (i) A faster reaction has a steeper line than a slower reaction. When the reaction is finished, there is no more increase in the volume of gas given off. Describe how the rate of the reaction changes during the course of this reaction. Explain how your graph shows these changes. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (ii) The student repeats the experiment using the same amounts of calcium carbonate and dilute hydrochloric acid. This time, the acid is at a higher temperature. The rate of reaction increases. Draw a line on the grid in (d) to show the results you expect from this faster reaction. Label the line F. [2] [Total: 15]

Mark scheme: 3(a)(i) (gas) syringe ; 1 3(a)(ii) burette / volumetric pipette ; 1 3(a)(iii) stops fizzing / no (more) gas collected / formed ; 1 3(b) solid / calcium carbonate and left (in the conical flask / at the end) ; 1 3(c) 34 ; 47 ; 2 3(d)(i) axes correct way round and labelled with quantity and unit ; axes linear and plotted points cover ⩾ ½ the grid ; points plotted correctly ; 3 Question Answer Marks 3(d)(ii) point at 180 s ; 1 3(d)(iii) line from origin showing curve and then level ; 1 3(e)(i) any 2 from: reaction is fast at the start as the graph is steep ; rate of reaction decreases / reaction slowing down as the curve gets less steep ; reaction stops and line is horizontal / reaction stops and volume stays the same ; 2 3(e)(ii) line drawn to the left of the original curve and doesn’t cross it at any point before it goes horizontal ; to same height ; 2

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4 Fig. 4.1 shows some of a student’s notes about testing for gases and ions. When dilute nitric acid and aqueous silver nitrate are added to chlorides, a white precipitate is made. When dilute nitric acid and aqueous barium nitrate are added to sulfates, a white precipitate is made. When aqueous ammonia is added to metal ions, a precipitate is often made. Iron(II) ions give a green precipitate, iron(III) ions a brown precipitate, copper ions a blue precipitate which dissolves in excess ammonia to give a dark blue solution, calcium a white precipitate and zinc a white precipitate that dissolves in excess ammonia. When aqueous sodium hydroxide is added to metal ions, a precipitate is often made. Iron(II) ions give a green precipitate, iron(III) ions a brown precipitate, copper ions a blue precipitate, calcium a white precipitate and zinc a white precipitate that dissolves in excess ammonia. Fig. 4.1 The student has aqueous calcium chloride and aqueous copper sulfate. Complete Table 4.1 with the results the student gets with these two solutions. Table 4.1 observations test aqueous calcium chloride aqueous copper sulfate add a few drops of aqueous ammonia add excess aqueous ammonia add a few drops of aqueous sodium hydroxide add dilute nitric acid and aqueous barium nitrate add dilute nitric acid and aqueous silver nitrate [5]

Mark scheme: 4 Test observations calcium chloride copper sulfate add a few drops of aqueous ammonia add excess aqueous ammonia white ppt ; (white ppt) blue ppt and dark blue solution / dissolves to give dark blue colour ; add a few drops of aqueous sodium hydroxide white ppt and blue ppt ; add dilute nitric acid and aqueous barium nitrate no ppt / colourless (solution) / no change / no reaction/ nothing happens and white ppt ; add dilute nitric acid and aqueous silver nitrate white ppt and no ppt / blue solution / no change / no reaction / nothing happens ; 5

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5 A student investigates the resistance of different combinations of identical lamps. The student sets up the circuit shown in Fig. 5.1. This is circuit 1. A circuit 1 X Y Fig. 5.1 (a) On Fig. 5.1, draw the symbol for a voltmeter connected to measure the potential difference between point X and point Y. [2] (b) Procedure The student: • connects the voltmeter into circuit 1 to measure the potential difference between X and Y • closes the switch • records in Table 5.1 the potential difference V and the current I • opens the switch. Table 5.1 circuit V / V I / A R / ........... 1 2 3.0 0.25 12 3 2.8 0.20 14 (i) Fig. 5.2 shows the readings on the voltmeter and the ammeter. 0.5 1 2 V A 0 3 0 1.0 Fig. 5.2 Record in Table 5.1 the values of the potential difference V and the current I. [2] (ii) Suggest why the student opens the switch after completing the procedure. ..................................................................................................................................... [1] (c) Procedure The student: • connects circuit 2 as shown in Fig. 5.3 A circuit 2 X Y Fig. 5.3 • connects the voltmeter to measure the potential difference between X and Y • closes the switch • records in Table 5.1 the potential difference V and the current I • opens the switch. The student repeats the procedure in (c) for circuit 3, shown in Fig. 5.4. A circuit 3 X Y Fig. 5.4 (i) Calculate and record in Table 5.1 the total resistance R in circuit 1. Use the equation shown. V R = I [1] (ii) Complete the headings in Table 5.1 with the unit for resistance. [1] (d) Another student suggests that if each lamp has the same resistance, the resistance R in circuit 3 should be equal to 1.5 times the resistance R in circuit 2. Two quantities can be considered equal, within the limits of experimental error, if their values are within 10% of each other. State if the results support the student’s suggestion. Justify your statement by doing a calculation using appropriate values of R from Table 5.1. statement .................................................................................................................................. justification ................................................................................................................................ ................................................................................................................................................... ................................................................................................................................................... [2] (e) Another student finds that in their circuit 3, the lamps do not light up. Suggest one observation that the student makes to check if one of the lamps is broken. ................................................................................................................................................... ............................................................................................................................................. [1] (f) The student extends the investigation and connects the 3 lamps together in parallel to make circuit 4. (i) In the space provided, draw the circuit diagram for circuit 4. [2] (ii) State the name of a component that can be connected in series with the power supply in circuit 4 that will allow the brightness of the lamps to be changed. ..................................................................................................................................... [1] [Total: 13]

Mark scheme: 5(a) correct symbol ; correct parallel connection ; 2 5(b)(i) V = 2.9 ; I = 0.61 ; 2 5(b)(ii) cell/power supply may run down / wires may heat up ; 1 5(c)(i) 4.8 / 5 ; 1 Question Answer Marks 5(c)(ii)  / ohm ; 1 5(d) 12  1.5 times = 18 10 18 is 1.8 / 10 gives 16.2 AND not within 10 10 14 is 1.4 / 10 gives 15.4 AND not within 10 2 5(e) check if the ammeter gives a reading ; 1 5(f)(i) 3 lamps connected in parallel ; 3 lamps drawn and rest of circuit correct ; 2 5(f)(ii) variable resistor ; 1

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6 Plan an experiment to investigate how the area of the water surface in a beaker affects the rate of cooling of hot water in the beaker. Fig. 6.1 shows the area of the water surface. area of the water surface 100 APPROX 80 60 100 ml 40 water 20 Fig. 6.1 You are provided with: • a supply of hot water • a set of different sized beakers made from the same material, but with different areas of water surface. The beakers are lagged with insulation on their sides and bases. You may use any other common laboratory apparatus. Include in your plan: • any other apparatus needed • a brief description of the method, including what you will measure and how you will make sure your measurements are accurate • the variables you will control • a results table to record your measurements (you are not required to enter any readings in the table) • how you will process your results to draw a conclusion. You may include a labelled diagram if you wish. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 6 One mark from each section and any two others additional apparatus: stop-watch / timer ; thermometer ; measuring cylinder ; method: pour hot water into beaker and allow to cool/leave and more than one size / surface area ; measure temperature at start and end / time for a specific T drop / measure temperature every minute / time period ; 5 different sizes / surface areas ; repeat for each container ; table: columns for temperature and time / surface area against time ; with units ; control variables: volume of hot water ; initial hot water temperature ; room temperature ; time (of temperature loss) / temperature decrease ; processing and conclusion: calculate average to recognise / exclude anomalies ; calculate rate by loss of temperature  time ; calculate surface area by πr2 ; plot a graph of temperature against time / rate for each beaker and compare / surface area against time / rate ; use results to see whether increasing surface area increases or decreases the (rate of) temperature loss ; 7

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