A student determined the specific latent heat of vaporisation of water.
Figure 9 shows some of the equipment used.
This is the method used:
Put 50
Measure the mass of the beaker and water.
Use a heater to boil the water and keep it boiling for 600 seconds.
Measure the mass of the beaker and water after 600 seconds.
i- What measuring instrument should be used to measure the volume of water?
[1 mark]
SOLUTION
Measuring Cylinder
ii- What is a hazard in the student’s investigation?
[1 mark]
SOLUTION
III- What is a hazard in the student’s investigation?
The initial mass of the beaker and water was 0.080 kg. The final mass of the beaker and water was 0.071 kg.
The energy transferred by the immersion heater as the water boiled was 25 200 J.
Calculate the specific latent heat of vaporisation of water given by the student’s data. Give the unit.
Use the Physics Equations Sheet.
[5 marks]
SOLUTION
Let us first measure the mass of water.
m a s s o f w a t e r = i n i t i a l m a s s - f i n a l m a s s
m a s s o f w a t e r = 0.080 - 0.071
m a s s o f w a t e r = 0.080 - 0.071
m a s s o f w a t e r = 0.009 k g
Now, use
E = m L
L = E m = 252 00 0.009 J k g
Iv- Some thermal energy was transferred to the surroundings while the water was being heated.
Explain how this affected the student’s value for the specific latent heat of vaporisation of water.
[ 2 marks]
SOLUTION
Less than 2 5200 J
v- Some of the water evaporated before its temperature reached 100 °C.
Explain how this affected the student’s value for the specific latent heat of vaporisation of water.
[2 marks]
SOLUTION
The measured change in mass would be greater than the actual change. Hence, the value measured by student would be smaller than the actual.
