In this experiment, you will investigate how the temperature of the surroundings affects the rate of cooling of water. You are provided with: • stop-watch • a 250 cm³ beaker • a larger beaker (500 cm³ or 600 cm³) • a thermometer • a supply of hot water • a supply of mixed ice and water • paper towels to mop up spillages.

1. (a)Ask the supervisor to pour approximately 100 cm³ of hot water into the 250 cm³ beaker.
2. (a)(i)Measure the temperature θ of the water and immediately start the stop-watch. Record this temperature in the first row of Table 2.1.[1]
3. (a)(ii)Record in Table 2.1 the temperature θ of the water every 30s for 4 minutes. [Table 2.1] Empty the 250 cm³ beaker when you have finished taking the temperature of the water in it.[1]
4. (a)(iii)Calculate the average cooling rate C₁ of the water for the first 90s of the experiment. Use your readings in Table 2.1 and the equation: C₁ = (θ₀ - θ₉₀)/t where θ₀ is the temperature at 0s, θ₉₀ is the temperature at 90s and t is the time of 90s. Give the unit for C₁. C₁ = .................................................... unit ............ [2]
5. (a)(iv)Calculate the average cooling rate C₂ of the water for the final 90s of the experiment. Use the equation: C₂ = (θ₁₅₀ - θ₂₄₀)/t where θ₁₅₀ is the temperature of the water at 150s, θ₂₄₀ is the temperature of the water at 240s and t is the time of 90s. C₂ = .................................................... unit ............ [1]
6. (a)(v)Compare your values of C₁ and C₂. Explain any difference in these values.[1]
7. (b)Pour approximately 100 cm³ of iced water into the larger beaker. Ask the supervisor to pour approximately 100 cm³ of hot water into the 250 cm³ beaker. Carefully place the 250 cm³ beaker of hot water into the larger beaker of iced water as shown in Fig. 2.1. Make sure that the water from the larger beaker does not spill into the smaller beaker. [Figure 2.1]
8. (b)(i)Measure the temperature θ of the hot water and immediately start the stop-watch. Record, in Table 2.2, the temperature at times t = 0s, 30s, 60s, 90s and 120s. [Table 2.2][1]
9. (b)(ii)Calculate the average cooling rate C₃ for the first 90s of the experiment. Use your readings in Table 2.2 and the equation: C₃ = (θ₀ - θ₉₀)/t C₃ = .................................................... unit ............ [1]
10. (b)(iii)Describe how C₃ differs from C₁. Explain your answer.[1]
11. (b)(iv)State one variable that you should keep constant to make a valid comparison of C₁ and C₃.[1]

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