Ice Experiments – Making Frost

Today is day 2 of our week of icy experiments, you can see yesterdays fun with freezing here.

When we left the house yesterday to go to school, Z and S were fascinated by the frost on the car and ground, so we thought we would try to make some at home.

A clean and empty tin can

Crushed ice

Water

Salt

How to make frost on a can

Fill the tin can about half full with ice and add some salt and water.

Wait and watch the frost form.

How does frost form?

The air around us can hold a lot of water which is called water vapour.  You can’t see it but it’s usually there (especially in a kitchen).  We can often see this water vapour when it condenses on windows, cars, grass and cobwebs.  We call this dew.  Cold surfaces generally make the water vapour condense because colder air can’t hold as much water so what it can’t hold turns into droplets on surfaces.

 If the surface is very cold (below the freezing point of water) the condensed water vapor freezes, this is what we see as frost.

In our experiment we filled a can with crushed ice and a bit of water.  This makes the water and the can sit at around the freezing point of water (zero degrees Celsius).  However we need to get it even colder and we do this by adding salt.  Salt lowers the melting point of ice (and we might investigate this process later on), but by doing so it means that the surface of the can is actually below freezing point.  This makes the water vapour in the air (and you can make sure there is some by putting the can on a wet paper towel) condense and freeze on the can.

Look closely at the frost, you can see crystals of ice growing on each other.  Next time you see frost outside take a closer look

See here for more ice experiments.