Properties of water and ice. STEM session plan.
Water seems boring – no color, taste, or smell. However, it has amazing properties that are fascinating and useful. Investigate what happens to the water when you put it into the freezer. This simple STEM experiment demonstrates the principle that ice takes up more space than its equivalent as water.
Timing: 10 min preparation. Overnight freeze. 15–20 min to examine the result and run follow-up experiments.
Materials: Plastic cup (avoid glass cup as frozen water can break the glass), water, freezer, tub.
Preparation and investigation: fill the plastic cup with water almost up to the brim, leaving some space. If there is enough space in the freezer, let each student fill their cups and put students’ names on it. Put the cups in the freezer overnight.
The next day take the cups out of the freezer and observe what happened to the water.
Trigger questions: What happened to the water? How does the ice feels? Did you notice that the block of ice is larger than the top of the cup?
Enrichment: Take the ice out o f the cup and place it into the tub with water. What happens to the ice? Does it sink or float? What happens to the ice after some time? Has it disappeared?
What is happening?
Usually, when things freeze – in other words when they turn from a liquid into a solid – they shrink or get smaller. This is because, normally, if you make something hotter, it the molecules inside it vibrate more. When it vibrates more, it tends to take up more space, so it tends to expand.
Ice is very unusual in that, as it gets colder, although the particles are certainly vibrating less, it nonetheless expands or gets larger. When water freezes, the molecules get themselves into the most stable configurations and align in specific order. This order takes up more volume than the random orientation the water molecules can achieve in the liquid phase.
When liquid water is cooled, it contracts like one would expect until a temperature of approximately 4 degrees Celsius is reached. After that, it expands slightly until it reaches the freezing point, and then when it freezes it expands by approximately 9%.
So, the water molecules are slightly further apart when in solid form than when in liquid form. The mass of water in solid state stays the same as in a liquid form but the volume has increased, the density of the ice is reduced compared to the liquid water. This is the reason why ice can float on the water.
Did you know that when water finds its way into rock cracks freezes later, it expands and can split off a piece of rock.