Practical 12
Latent Heat of Vaporisation of Water
Introduction
In this experiment steam will be passed into an insulated cup (calorimeter) containing
water at a known temperature, as the steam condenses in the water it will give heat to
the water causing the temperature to rise. By measuring the rise in temperature of the
water the latent heat of vaporisation can be calculated.
Procedure
 Make sure there is water in the steam generator and switch it on. While you
are waiting for it to boil measure the mass of the calorimeter fill it half full of
water, measure it’s mass again to determine the mass of water.
 Measure the temperature of the water
 When the water is boiling steadily pass the steam into the cold water. The
steam must be passed through a water trap to catch any water droplets that
might escape with the steam.
Water Trap
Steam Generator

Calorimeter
When the temperature has risen by 10°C take out the tube delivering the steam
and switch off the heater.
 Determine the mass of condensed steam.
 Estimate the uncertainties in all your measurements.
Analysis
Given that:
Heat from condensing steam + Heat from condensed steam cooling = Heat to water
Write an equation and calculate the latent heat of vaporisation of water.
Calculate the uncertainty in the final result.
Compare your result with the value in the book. Is (your value – the book value)
greater than or less than the uncertainty in your measurements? If the difference is
too big, comment on why this might be so. How could the experiment be improved?
If you have time repeat the experiment with your suggested improvements.