Liquid and solid water; the growth of ice crystals

Depending on how you approach this topic, the activity should take between one and two hours.

Equipment

Materials per group

• Ice
• Water

Equipment per group

• Molecular models
• Laboratory glassware – eg beakers
• Measuring cylinders
• Thermometer
• Stop-watch
• Safety glasses

Health, safety and technical notes

• Read our standard health and safety guidance here.
• Wear eye protection.
• Observing ice melting is not hazardous, though work with supercooled water could be. 
• This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete. 

Commentary

Liquid water is made up of clusters of water molecules joined together by hydrogen bonds, which are continually breaking and reforming.

As they turn into solid ice, they become fixed into the three-dimensional pattern of the crystal. The hydrogen bonds hold the molecules further apart in ice so that it is less dense than water. This activity is intended to encourage students to think more deeply about the process of freezing.

After learning about hydrogen bonding, the students may explore the arrangement of the atoms in space by building a model of an ice structure.

They can work in groups to do this, each student constructing a few molecules and then joining them together. Orbital molecular models are very suitable. This in itself is an exercise in group problem-solving and may be done as a competition

Extension

This topic lends itself well to a discussion based on ‘What if?’ Students could discuss what would happen if ice were not less dense than water, if it was a good conductor of heat, etc.

When ice grows in a living system, the process causes violent changes within the cells. Cryobiologists look at the biological effects of this phase change. They study the effects of low temperature on living things – food preservation is an important application.

The phase change that occurs when a liquid metal solidifies is of great importance in metallurgy. Again, heat dissipation is significant as it can determine the direction of growth of crystals in the melt. By controlling the heat flow, it is possible to produce a turbine blade made of a single crystal.

Notes

This resource is part of a collection of problem-solving activities, designed to engage learners in small group work. Find out how to use these resources, and obtain a list of suggested ‘junk items’ here.