# Saturated and Unsaturated Vapour Pressure

## Saturated and Unsaturated Vapour Pressure

What is a saturated solution?

If in a water sugar solution, the amount of dissolved sugar is equal to the
maximum amount that a given amount of water can dissolve at a certain
temperature, then that solution is called a saturated solution.

What is an unsaturated solution?

If in a water sugar solution, the amount of dissolved sugar is less than that
amount that a given amount of water can dissolve at a certain temperature,
then that solution is called a saturated solution.

What is saturated vapour?

At a certain temperature in an enclosed space, if the amount of vapour present
is equal to the maximum vapour capacity of that space, then that vapour is
called saturated vapour.

What is unsaturated vapour?

At a certain temperature in an enclosed space, if the amount of vapour present
is less than the maximum vapour capacity of that space, then that vapour is
called unsaturated vapour.

What is vapour pressure?

Vapour enclosed in a container behaves like gas which means vapour molecules
move randomly and erratically in different directions and collide with each
other and the container wall and as a result, create pressure. This pressure
is called vapour pressure.

What is saturated vapour pressure?

The pressure of saturated vapour at a certain temperature is called saturated
vapour pressure.

What is unsaturated vapour pressure?

The pressure of unsaturated vapour at a certain temperature is called
unsaturated vapour pressure.

What is called Torricelli’s vaccum?

When a one-meter-long one-end closed glass tube is filled with pure mercury
and is put upside down on a mercury-filled pot, the mercury level inside the
glass tube goes down a little and settles down at a certain height and thus a
vacuum is created on top of the mercury. This void is called Torricelli’s
vacuum.

Saturated vapour pressure increases with temperature rise

If the temperature of Torricelli’s vacuum is increased when that space is
saturated with vapour, it is seen that more water is evaporating and mercury
column height is going down. Therefore, it can be realized that saturated
vapour pressure increases with temperature rise.

Saturated vapour pressure doesn’t depend on vapour volume

Having Torricelli’s vacuum saturated with water vapour, if the glass tube is
gradually lowered, it is seen that the volume of Torricelli’s vacuum is
decreasing while mercury column height remains the same even if it remains so
until Torricelli’s vacuum disappears. It can be postulated from this event
that at a fixed temperature, saturated vapour pressure doesn’t depend on the
volume of vapour.

Saturated vapour pressure depends on the nature of liquid

If any liquid other than water is inserted into Torricelli’s vacuum, it is
seen that saturated vapour pressure is different from that of water.