Onions are vegetables that are harvested from the plant Allium cepa. In many countries, small onions are used to make pickled onions. Pickled onions can be stored for a long time because the growth of microorganisms is prevented. Pickled onions are made using this method. • Remove the dry outer layer from small onions. • Place the onions in a sodium chloride solution for several hours. • Remove the sodium chloride solution and place the onions in a solution of ethanoic acid (vinegar). Fig. 1.1 shows a container of pickled onions and some fresh onions that have not been pickled. dry outer layer of onion container of pickled onions fresh onion [Figure 1.1]

1. (a)(i)Some students decided to investigate how placing small onions in different concentrations of sodium chloride solution affects the mass of the onions. Identify the independent variable in this investigation.[1]
2. (a)(ii)The students were given a 20.0% stock solution of sodium chloride. The students decided to use the stock solution to make sodium chloride solutions with concentrations of 0.0%, 1.0%, 5.0%, 10.0%, 15.0% and 20.0%. The students made 140 cm³ of these solutions in separate beakers. Complete Table 1.1 to show how 140 cm³ of these solutions could be made by proportional dilution of the 20.0% stock solution of sodium chloride. Table 1.1 percentage concentration of sodium chloride solution volume of 20.0% sodium chloride solution /cm³ volume of /cm³ 0.0 1.0 5.0 10.0 15.0 20.0[2]
3. (b)(i)The students carried out this procedure. • The dry outer layer was removed from 30 small onions. • Five of the small onions were placed into each of the six beakers containing the sodium chloride solutions prepared by the students. • The onions were left in the sodium chloride solutions for 2 hours. • The mean percentage change in mass of the five small onions in each beaker was calculated. The students then repeated the whole procedure using a new set of 30 small onions. This time the onions were left in the sodium chloride solutions for 48 hours. Fig. 1.2 shows the results of the investigation. [Figure 1.2] Explain why the students calculated the percentage change in mass of the onions.[1]
4. (b)(ii)One of the students concluded that: The water potential of the onion cells is the same as the water potential of a 4.2% sodium chloride solution. With reference to the information provided, including the results shown in Fig. 1.2, suggest reasons why this conclusion should not be accepted.[4]
5. (c)(i)The turnip, Brassica rapa, is a root vegetable. Turnips are grown in many parts of the world. Fig. 1.3 shows freshly harvested turnips with the leaves still attached. [Figure 1.3] A student decided to investigate the effect of temperature on the rate of osmosis in turnips. In an initial test, the student removed the outer layer from a turnip and cut the turnip into small blocks. The student placed one of the turnip blocks into a beaker of distilled water, as shown in Fig. 1.4. Water entered the block by osmosis. [Figure 1.4] The student was provided with additional turnips and standard laboratory apparatus. Describe a method that the student could use to investigate the effect of increasing the temperature, over a range from 10°C to 50 °C, on the rate of osmosis in turnip blocks. Do not include the risk assessment or how to calculate the rate of osmosis from the results. Your method should be set out in a logical order and be detailed enough to allow another person to follow it.[6]
6. (c)(ii)Complete the sketch graph shown in Fig. 1.5 to predict the effect of increasing the temperature, over a range from 10°C to 50°C, on the rate of osmosis in turnips. Include axis labels with units in your answer. [Figure 1.5][2]
7. (c)(iii)Suggest one hazard of your method in (c)(i), the risk associated with the hazard and the precaution that would need to be taken. hazard risk precaution[1]

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