You are provided with a measuring cylinder, two different tins labeled C and D, a thermometer, and other necessary materials. Use the measuring cylinder pro...
Question 1 Report
- You are provided with a measuring cylinder, two different tins labeled C and D, a thermometer, and other necessary materials.
- Use the measuring cylinder provided to measure 100 cm of water and pour it into the tin label.
- Heat the water in the tin almost to boiling (90°C).
- Remove the tin and place it on a cork or wooden stand.
- Insert the thermometer into the tin and record the temperature of the water every minute starting from 85°C until the temperature falls to 60°C.
- Repeat the experiment with the tin labeled D using exactly the same volume of water and temperature range. Tabulate your readings.
- On the same graph sheet and using the same axis and scales, plot two graphs of temperature on the vertical axis and time on the horizontal axis from the readings obtained using tins C and D.
- Label the graphs appropriately as C and D to correspond with the tins used.
- From each graph, read off the time taken to cool from 85°C to 65°C.
- State two precautions taken to ensure accurate results.
(b)i. Explain how heat losses by radiation and convection are minimized in a vacuum flask.
ii. State four factors that affect the rate of evaporation of a liquid in an open container.
Answer Details
(a) Cooling curves for tins C and D
100 cm3 of water was used in each tin. The temperature was recorded at one-minute intervals as the water cooled.
| Time, t (min) | Temperature in tin C, T (°C) | Temperature in tin D, T (°C) |
|---|---|---|
| 0 | 85 | 85 |
| 1 | 83 | 84 |
| 2 | 81 | 83 |
| 3 | 79 | 81 |
| 4 | 78 | 79 |
| 5 | 75 | 78 |
| 6 | 73 | 76 |
| 7 | 71 | 75 |
| 8 | 70 | 73 |
| 9 | 68 | 71 |
| 10 | 66 | 69.5 |
| 11 | 65 | 68 |
| 12 | 63 | 66 |
| 13 | 62 | 64 |
| 14 | 60 | 62 |
| 15 | – | 61 |
| 16 | – | 60 |
The two cooling curves, plotted on the same axes, are:
From the graph:
- Time for tin C to cool from 85 °C to 65 °C = 11.0 min.
- Time for tin D to cool from 85 °C to 65 °C = 12.4 min.
Precautions
- Use the same volume of water and the same initial temperature in both tins.
- Keep the thermometer bulb fully immersed without touching the base or side of the tin; stir the water gently before taking each reading and read the thermometer at eye level.
(b)(i) Vacuum flask
The silvered surfaces of the double walls reflect thermal radiation and are poor emitters and absorbers; hence heat loss by radiation is minimized. The vacuum between the walls contains virtually no particles, so convection currents cannot occur. The insulating stopper also prevents air circulation at the neck of the flask.
(b)(ii) Factors affecting evaporation
- Temperature of the liquid.
- Area of the liquid surface exposed.
- Humidity of the surrounding air.
- Speed of air movement or draught over the surface.
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