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Chemistry Practical Work The Cooling Curve of Water
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Introduction
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Hot water loses heat when it is left at room temperature. The heat moves from the hot water into the surrounding air.
Aim
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To find out the rate of loss of heat from a hot water.
Method
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1. Set up the apparatus as shown in the photograph below. (N.B.
You must practise using the Bunsen burner before you carry out this experiment).
2. While you are waiting for the water to boil prepare your results table. When the water starts to boil turn the Bunsen burner off at the gas tap.
3. Take a centigrade thermometer and a stop watch. Place the bulb of the thermometer in the hot water so that it is in the water but not touching the glass beaker at all. Hold the thermometer at an angle so as not to burn your hand.
4. Record the temperature and immediately start the stop watch.
5. Repeat point 4. every 30 seconds for 10 minutes.
Results
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Record your results a table:
| Time (min) |
Temperature (°C) |
| 0,0 |
|
| 0,5 |
|
| 1,5 |
|
| 2,0 |
|
| 2,5 |
|
| 3,0 |
|
| 3,5 |
|
| 4,0 |
|
| 4,5 |
|
| 5,0 |
|
| 5,5 |
|
| 6,0 |
|
| 6,5 |
|
| 7,0 |
|
| 7,5 |
|
| 8,0 |
|
| 8,5 |
|
| 9,0 |
|
| 9,5 |
|
| 10,0 |
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Now make a graph of your results with Time (mins) on the horizontal axis and Temperature (°C) on the vertical axis. (N.B.
Information about drawing line graphs).
Conclusion
What shape is your graph? Does it show that hot water loses heat at the same rate over 10 minutes or that the rate of heat loss changes with time?
N.B. A straight line would indicate a constant rate of heat loss. A curved line would indicate that the rate changes.
What happens to the rate of heat loss as the water in the beaker cools down?
Do you think there will come a time when the water in the beaker is no longer losing heat? Explain your answer.
If the water in the beaker stopped losing heat but you continued to take its temperature for a few minutes, what do you think would happen to the line of the graph?
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