(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.
| Table of value (observation) | |||
| S/N | t(min) | Tc(°C) | To(°C) |
| 1 | 0.00 | 85.00 | 85.00 |
| 2 | 1.00 | 83.00 | 84.00 |
| 3 | 2.00 | 81.00 | 83.00 |
| 4 | 3.00 | 79.00 | 81.00 |
| 5 | 4.00 | 78.00 | 79.00 |
| 6 | 5.00 | 75.00 | 78.00 |
| 7 | 6.00 | 73.00 | 76.00 |
| 8 | 7.00 | 71.00 | 75.00 |
| 9 | 8.00 | 70.00 | 73.00 |
| 10 | 9.00 | 68.00 | 71.00 |
| 11 | 10.00 | 66.00 | 69.50 |
| 12 | 11.00 | 65.00 | 68.00 |
| 13 | 12.00 | 63.00 | 66.00 |
| 14 | 13.00 | 62.00 | 64.00 |
| 15 | 14.00 | 60.00 | 62.00 |
| 16 | 15.00 | - | 61.00 |
| 17 | 16.00 | - | 60.00 |
Time taken to cool from 85°C to 65°C
Tin C = 11 minutes
Tin D = 12.40 minutes
Precautions: i
- ensured there was no error due to parallax when reading my thermometer.
- ensured that the liquid in the tins was gently stirred.
(b)i. Silvered wall minimized radiation.
Insulating cork minimized convection.
(i) Factors affecting the rate of evaporation.
- Temperature
- Nature of liquid.
- Humidity
- Area of liquid surface exposed
- Draught
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