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. You are going to investigate the effect of temperature on the rate of osmosis. Read all the instructions but DO NOT CARRY THEM OUT until you have drawn a table for your results in the space provided in 1(a)(ii). You should use the safety equipment provided while you are carrying out the practical work. Step 1 Label one empty 100 cm3 beaker cold raisins and one empty 100 cm3 beaker hot raisins. Step 2 Label one paper towel cold and one paper towel hot. Step 3 Take 15 raisins and line the raisins up, touching end to end along a ruler, as shown in Fig. 1.2. 0 1 2 3 4 5 6 7 8 9 Fig. 1.2 Step 4 Measure the length of the line of raisins. Record your measurement in your table in 1(a)(ii). Step 5 Place the 15 raisins from step 4 into the empty beaker labelled hot raisins. Step 6 Repeat steps 3 and 4 with a second group of 15 raisins. Place these raisins into the empty beaker labelled cold raisins. Step 7 Raise your hand when you are ready for hot water to be put into the 250 cm3 beaker labelled hot water. Step 8 Put 50 cm3 of hot water into the beaker labelled hot raisins. Step 9 Put 50 cm3 of cold water into the beaker labelled cold raisins. Step 10 Start the stop-clock. Step 11 Measure the temperatures of the water in the beakers labelled cold raisins and hot raisins and record your measurements in 1(a)(i). Step 12 Leave the raisins to soak for 20 minutes. Continue with the rest of the questions while you are waiting. Step 13 After 20 minutes, measure the final temperatures of the water in the beakers labelled cold raisins and hot raisins and record your measurements in 1(a)(i). (a) (i) Record the temperatures of the water in the beakers. Include the unit. water temperature in the cold raisins beaker in step 11 …… water temperature in the hot raisins beaker in step 11 …… water temperature in the cold raisins beaker in step 13 …… water temperature in the hot raisins beaker in step 13 …… [2] Step 14 Place the sieve over the waste container. Tip the contents of the cold raisins beaker into the sieve. Place the raisins from the sieve onto the paper towel labelled cold. Step 15 Line up the 15 raisins so that they are touching end to end along the ruler. Measure the length of the line of raisins. Record your measurement in your table in 1(a)(ii). Step 16 Repeat steps 14 and 15 using the hot raisins beaker and the paper towel labelled hot. (ii) Prepare a table to record your results from steps 4, 6, 15 and 16. [4] (iii) Use the information in your table in 1(a)(ii) to calculate the change in length for each group of 15 raisins. change in length of cold raisins …… change in length of hot raisins …… [1] (iv) State a conclusion for your 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 15 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) four temperatures recorded and the hot temperature higher than 2 the cold temperature in step 11 ; °C ; 1(a)(ii) table drawn with minimum of three columns and headings 4 underlined ; headers and length units correct ; R if units in body of table four lengths recorded ; final ‘hot’ lengths higher than initial ‘hot’ lengths ; e.g. beaker initial length final length / temperature / mm / mm cold hot check supervisor’s report if results not as expected 1(a)(iii) correct calculation for both from candidate’s data ; 1 1(a)(iv) conclusion that matches the candidate’s results ; 1 expected: higher temperature increases the rate of osmosis / more water moves into 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