In this experiment you will investigate the rate of cooling of hot water in a test-tube under different conditions. You are provided with: • a test-tube • a 250 cm³ glass beaker • a thermometer, –10°C to 110°C, graduated in 1°C intervals • a 100 cm³ or 250 cm³ measuring cylinder • a stop-watch • a clamp, boss and stand • a supply of hot water (approximately 80°C) • a supply of cold water (at room temperature) • a supply of warm water (approximately 40°C). (a) The test-tube has been arranged as shown in Fig. 2.1. [Figure 2.1] • Pour 200 cm³ of cold water into the beaker. • Ask the supervisor to pour hot water into the test-tube until it is approximately one-third full. • Lower the test-tube into the beaker of cold water until the level of the hot water in the test-tube is below the level of the cold water in the beaker. See Fig. 2.2. [Figure 2.2] • Place the thermometer into the test-tube. • Wait for approximately 30s before measuring the temperature and starting the stop-watch.

1. (a)(i)Measure the temperature θ of the hot water in the test-tube and start the stop-watch immediately. Record the temperature at time t = 0 in the second column of Table 2.1.[1]
2. (a)(ii)Measure the temperature θ of the hot water every 30s for 180 s. Record your readings in the second column of Table 2.1.[2]
3. (b)Describe in detail one precaution that you take to make sure that the temperature measurements are as accurate as possible.[1]
4. (c)Empty the test-tube. • Empty the cold water from the beaker. • Pour 200 cm³ of warm water into the beaker. • Ask the supervisor to pour hot water into the test-tube until it is approximately one-third full. • Lower the test-tube into the beaker of warm water until the level of the water in the test-tube is below the level of the warm water in the beaker. • Place the thermometer into the test-tube. • Wait for approximately 30s before measuring the temperature and starting the stop-watch. Repeat the steps described in (a)(i) and (a)(ii), recording your results in the third column of Table 2.1.[2]
5. (d)Calculate the temperature decrease of the hot water in the test-tube after cooling for 180s in both the beaker of cold water and the beaker of warm water. Use your temperature readings in Table 2.1. temperature decrease when cooling in the cold water = .................... °C temperature decrease when cooling in the warm water = .................... °C[1]
6. (e)(i)Use your answers to (d) to decide how the temperature of the water in the beaker affects the rate of cooling of hot water in the test-tube. State your conclusion.[2]
7. (e)(ii)Suggest one improvement to the experimental procedure described in (a) and (c) that allows a more valid comparison to be made between the two rates of cooling.[1]

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