Question 122 marks
Question
Fig. 1.1 shows some raisins, which are made by drying grapes. Raisins contain high concentrations of sugars. Fig. 1.1 Osmosis is the movement of water across a partially permeable membrane from a dilute solution to a concentrated solution. A student investigated the effect of temperature on the rate of osmosis. Step 1 The student labelled one empty beaker cold and one empty beaker hot. Step 2 50 cm3 of cold water was poured into the cold beaker. Step 3 10 raisins were lined up along a ruler. Each raisin was touching end to end. Step 4 The total length of the line of 10 raisins was measured. The student recorded this measurement in their notebook. Step 5 The group of 10 raisins was placed in the cold beaker. Step 6 50 cm3 of hot water was poured into the hot beaker. Step 7 A second group of 10 raisins was lined up along the ruler, each touching end to end. The length of the line was measured and recorded. Fig. 1.2 shows the measurements the student recorded during step 4 and step 7. cold beaker raisins 112 mm hot beaker raisins 115 mm Fig. 1.2 Step 8 The second group of 10 raisins was placed in the hot beaker. Step 9 The temperatures of the water in each beaker were measured. The thermometers are shown in Fig. 1.3. 30 45 25 40 20 35 cold hot beaker beaker Fig. 1.3 (a) (i) State the temperatures shown on the thermometers in Fig. 1.3. Include the unit. water temperature in the cold beaker …… water temperature in the hot beaker …… [2] Step 10 A stop-clock was started. Step 11 After 20 minutes, the raisins were removed from the cold beaker. Step 12 The cold beaker raisins were lined up along the ruler, touching end to end and the total length of the 10 raisins was measured. Step 13 Step 11 and step 12 were repeated for the hot beaker raisins. A drawing of the two lines of raisins from step 12 and step 13 is shown in Fig. 1.4. cold beaker raisins 0 1 2 3 4 5 6 7 8 9 10 11 12 13 ruler hot beaker raisins 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Fig. 1.4 (ii) Prepare a table to record the results. Complete the table by: • recording the measurements shown on the notebook in Fig. 1.2 • measuring and recording the length of the lines of raisins shown in Fig. 1.4. [4] (iii) Use the information in your table in 1(a)(ii) to calculate the change in length for each group of 10 raisins. change in length of the cold beaker raisins …… change in length of the hot beaker raisins …… [1] (iv) State a conclusion for these results. …… [1] (b) (i) State one variable that was kept constant in this investigation. …… [1] (ii) Suggest why it was better to measure the total length of 10 raisins touching end to end rather than just measuring the length of one raisin. …… [1] (c) A student investigated the effect of different concentrations of sodium chloride solution on osmosis in potatoes. The student used this method: • Make four different concentrations of sodium chloride solution in separate test-tubes. • Cut a piece of potato into five cylinders that are approximately the same length and diameter. • Measure and record the mass of each potato cylinder. • Put one potato cylinder into a test-tube containing distilled water. • Put one potato cylinder into each of the four test-tubes containing the different sodium chloride solutions. • Leave the potato cylinders in the test-tubes for 30 minutes. • After 30 minutes, remove the potato cylinders from the test-tubes. • Dry the potato cylinders with a paper towel. • Measure and record the mass of each potato cylinder. (i) State the variable that was measured (dependent variable) in this investigation. …… [1] The student’s results are shown in Table 1.1. Table 1.1 concentration of sodium chloride potato cylinder potato cylinder percentage solution initial mass / g final mass / g change in mass / mol per dm3 0.0 1.13 1.32 16.8 0.2 1.03 1.08 4.9 0.4 1.19 1.06 –10.9 0.6 1.13 0.86 –23.9 0.8 1.14 0.82 (ii) Using the information in Table 1.1, calculate the percentage change in mass for the potato cylinder in the 0.8 mol per dm3 sodium chloride solution. Give your answer to one decimal place. Space for working. …… % [3] (iii) Using the data in Table 1.1 and your answer to 1(c)(ii), plot a line graph on the grid of the concentration of sodium chloride solution against the percentage change in mass. One axis has been started for you. 0.0 [4] (iv) Estimate the concentration of sodium chloride solution at which there would be no percentage change in the mass of the potato cylinder. Show on your graph how you obtained your estimate. …… mol per dm3 [2] (v) Suggest why the student calculated the percentage change in mass rather than using the difference in the mass of the potato cylinders. …… [1] (vi) Suggest why the student dried the potato cylinders before measuring their mass. …… [1] [Total: 22]
Mark scheme
1(a)(i) temperatures recorded as 21.5 and 41(.0) ; 2 °C ; 1(a)(ii) table drawn with minimum three columns and headings underlined ; 4 headers and length units correct ; four lengths recorded including 112 and 115 in correct positions ; R if units in body of table correct final length measurements from Fig 1.4 i.e.,117±1 and 124±1 ; e.g. beaker initial length final length / temperature / mm / mm cold 112 117 ±1 hot 115 124 ±1 1(a)(iii) correct calculation for both ; 1 ecf for incorrect measurements in 1(a)(ii) cold = 5 (mm) hot = 9 (mm) 1(a)(iv) higher temperature increases the rate of osmosis / more water moves 1 into the raisins / AW, in hot water (compared to cold) / ora ; 1(b)(i) any one from: 1 type of raisin / fruit ; volume of water added ; number / amount, of raisins in each group ; orientation of raisins ; time left in water ; 1(b)(ii) any one from: 1 each raisin has only small change / a large group will give a larger change ; smaller percentage error in a large measurement / larger measurement more accurate ; some of the raisins may not change as expected / AW ; 1(c)(i) mass (of potato cylinder) ; 1 1(c)(ii) –28.1 (%) ;;; 3 MP1 correct figures selected from table 1.14 and 0.82 or 0.32 MP2 correct calculation and answer to any number of decimal places MP3 correct rounding to one decimal place ecf for incorrect MP2 and MP3 from incorrect previous step 1(c)(iii) axes labelled with units ; 4 suitable even scale and plotting area occupies at least half the grid in both directions ; at least four points plotted accurately ± half a small square ; suitable line drawn ; 1(c)(iv) correct reading from candidate’s graph ; 2 indication on the graph of where reading taken ; 1(c)(v) starting mass was not the same / to allow a comparison / AW ; 1 1(c)(vi) remove any excess solution so that it is not included in the mass ; 1