Why should crushed ice be used in the experiment

1
Why should crushed ice be used in the experiment?
To increase the surface area of ice andkeep good
contact with the heater. Crushed ice should be
used because this enhances the thermal contact
between the ice and the heater. Therefore, less
heat is wasted to heat up the air between the ice
cubes.
Would you expect the value of the specific latent
heat of fusion of ice obtained in the experiment
to be higher than, equal to, or lower than the
accepted value? Explain briefly.
The value obtained is higher than the accepted
value. This is because some energy supplied by
the heater is lost to the surroundings. The
actual energy absorbed by the ice should be
lesser.
2
Describe, with the aid of a diagram, how a
control set can be set up to improve the accuracy
of the experiment.
An immersion heater is set up without connecting
to the power supply. The actual mass of ice
melted by the energy supplied by the heater is
the mass difference between the masses of water
in the two beakers.
Why should the melting ice be used?
Melting ice is used to make sure that the
temperature of the ice is at 0 C. Hence, no
energy is absorbed as the heat capacity to raise
the temperature of the ice to 0 C.
3
Why is the control necessary?
This is to account for the ice melted at room
temperature.
After switching off the heater, the cups are not
removed until the drip rates become steady. Why?
This is to allow time for the energy from the
heater to be conducted to the ice to melt it
(water and ice are poor conductors of heat).
4
The immersion heater should not be switched on
unless it is fully immersed in water. Why?
Otherwise the heater may overheat and gets
damaged.
What are the possible sources of error in the
experiment?
5
A student suggests adding a lid on the beaker so
as to improve the accuracy of the experiment.
If the beaker is covered with a lid, the steam
will not be able to escape from the beaker. As a
result, water vapour will condense on the lid and
return back to the beaker. This will lead to a
serious experimental error.
Is the value of specific latent heat of
vaporization obtained in the experiment usually
higher or lower than the accepted value? Explain
briefly.
Due to the heat loss to the surroundings, the
energy recorded by the kilowatt-hour meter is
higher than the energy absorbed by the water. The
value obtained is usually higher than the
accepted value.
6
Comment on the statementThe calculated value of
the specific latent heat of vaporization of water
should be lower than the accepted value because
some boiling spills out from the cup.
Although water may spill out from the beaker, the
main source of error is due to the heat lost to
the surroundings. As the energy supplied is
always greater than the energy absorbed, the
calculated value would be greater than the
accepted value.
Suggest a method to improve the accuracy of the
experiment.
Use a polystyrene cup instead of a beaker because
polystyrene is a poor conductor of heat. Wrapping
the beaker with cotton wool.