procedure
1.heat water in the Beaker up to 100°C.
2.put off the burner.
3.when the water reaches 70°C, start measuring the temperature after every minute.
4.measure the temperature till the water reaches ambient temperature.
5.plot the graph of temperature versus time (in mins).
Answers
Introduction:
The rate at which an object cools (i.e. how quickly its temperature decreases) depends upon several factors, including:
Surface area
Volume
Type of insulation
Temperature difference with the surroundings
For this investigation, the effect of the temperature of water upon the rate of cooling will be investigated. The temperature-drop over 5 minutes (600 seconds) will be measured for 200ml of water at different start temperatures. The average rate of cooling can then be found by:
avg-rate-of-cooling = temperature drop/time
Apparatus:cooling
digital stopwatch
250ml beaker
rubber bung
thermometer
bunsen burner
tripod
gauze
retort stand and clamp
goggles
Control Variables:
Volume of water used: 150ml
Size of beaker (i.e. constant surface area): 250ml
Time interval of cooling: 5.0 minutes (600 seconds)
Temperature of the room: 21°C
Method:
Fill an empty beaker with exactly 150ml of water (check side-scale of beaker)
Set up apparatus as shown above. Ensure the thermometer is about 2cm above the bottom of the beaker.
Light the bunsen burner and put on a blue flame. Heat up the water.
When the temperature on the thermometer has reached 90°C, immediately switch off the burner.
Start the stopwatch and time for 5.0 minutes.
Read the thermometer value at the 5.0 minute mark.
Before repeating the experiment, check the level of water is still 150ml (some may have evaporated) and add more water if required.
For different start temperatures, repeat steps 3-7 but turn off the burner at the desired temperature.
Results:
Start Temperature of Water (°C) Temperature after 5min (°C) Drop in Temperature
(°C)
Average Rate of Cooling x 1000 (°C/s)
80 70 10 17
75 66 9 15
70 62 8 13
65 59 6 10
60 55 5 8
cooling-rate-graph
Conclusion:
There is a strong correlation between the average rate of cooling and the start temperature: the greater the start temperature, the faster the average rate of cooling.
