In this experiment you will investigate the rate of cooling of water at the top and at the bottom of a beaker of hot water. You are provided with: • a boss, clamp and stand • a 250 cm³ beaker • a thermometer • a stop-watch • a supply of hot water • paper towels to mop up any water spillages.

1. (a)• Ask your supervisor to pour hot water into the beaker until it reaches the 200 cm³ mark on the side of the beaker. • Lower the thermometer into the beaker by adjusting the position of the boss, until the bulb of the thermometer is just covered by the hot water. The arrangement of apparatus is shown in Fig. 2.1. [Figure 2.1] • Wait for approximately 30 s. • Start the stop-watch and read the thermometer.
2. (a)(i)Record the temperature reading at time t = 0 to the nearest 0.5 °C in the second column of Table 2.1. [1][1]
3. (a)(ii)• Wait for 3 minutes. Record the temperature reading at time t = 3.0 min in the second column of Table 2.1. [1] Table 2.1 time t/min bulb just below surface temperature/°C bulb just above bottom temperature/°C 0 3.0[1]
4. (a)(iii)Explain why you waited for 30 s before reading the initial temperature of the hot water. ......................................................................................................................................................... ......................................................................................................................................................... [1][1]
5. (b)• Remove the thermometer from the beaker and pour the water away. • Ask your supervisor to pour another 200 cm³ of hot water into the beaker. Repeat the procedure in (a) but positioning the thermometer lower in the beaker so that the bulb is just above, but not touching, the bottom of the beaker. The arrangement of apparatus is shown in Fig. 2.2. [Figure 2.2] Record the temperature of the water at times t = 0 and t = 3.0 min in the third column of Table 2.1 on page 6. [1][1]
6. (c)(i)Calculate the average rate of cooling P_T of the hot water at the top of the beaker. Use the equation: average rate of cooling = decrease in temperature of the water / time taken Give the unit of your answer. P_T = .............................................. unit ....................... [2][2]
7. (c)(ii)Calculate the average rate of cooling P_B of the hot water at the bottom of the beaker. P_B = .............................................. [1][1]
8. (d)(i)Use your results to suggest why a hot liquid should be stirred before measuring its temperature. ......................................................................................................................................................... ......................................................................................................................................................... [1][1]
9. (d)(ii)State one way in which the apparatus in this experiment is arranged to make it easy to read the thermometer accurately. ......................................................................................................................................................... ......................................................................................................................................................... [1][1]
10. (e)The experiment is repeated to check the results. Suggest one variable that must be kept constant. ......................................................................................................................................................... ......................................................................................................................................................... [1][1]

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