Try leaving a glass of tap water on the table for a day without touching it. You’ll notice the sides of the glass are speckled with bubbles. Where did this gas come from? It came right out of the water, in fact. As the water passed through the pipes on its way to your home, gases from the surrounding air were dissolved into it.
As the water warms, it is able to hold less gas. Boiling the water removes a lot of the dissolved gases in the water, just as a glass of water left out on a table will release bubbles.
Freezing the water does the same thing. Ice is formed as the water molecules line up with one another, which also pushes out dissolved gases and minerals. Because the water freezes from the top down, the dissolved gases are pushed slowly to the bottom until it collects into bubbles. Filtered water has less dissolved minerals in it, also making for clearer ice cubes. So should you be using non-filtered water for this activity, to make the difference more obvious?
When you think of snow, icebergs or glaciers, you rarely think of them as transparent. They are often shades of white or blue, and sometimes even pink or green. The reason has little to do with the ice itself, but what lies trapped in it.
As light passes through the solid ice and hits a bubble, it bends or ‘refracts’. Sometimes it will bend enough to bounce right back out again, reflecting most of the light and making the snow or iceberg look a bright white colour. If there is something in the ice capable of absorbing some of the light, like minerals or algae, it will bounce back a colour like green or pink.
Warning: This activity requires boiling water. Younger scientists should seek the help of an adult.
You will need
- A small pot
- Ice cube trays or small containers
- 1 litre bottle of filtered water
- A freezer
- A pen
What to do
- Pour half of your filtered water into a pot and boil it for at least five minutes. Let it cool and repeat.
- Fill one of your containers or ice cube trays with the remaining, non-boiled water.
- Once the pot has finished boiling, fill the second container with the hot water. Take care not to scald your hands.
- Place both containers into the freezer, using your pen and paper to keep a note or make a label detailing which one contains the boiled water.
- Wait two hours (if the containers are large, you might have to wait overnight).
- Take out the containers. If there’s ice on the outside of the containers, remove the ice before comparing them (you might need to run some warm water over the outside of them first).
- Which ice looks the clearest?