Ice is one of three physical states easily explored at home or in the classroom.
Live demonstration of science concepts can be applied both in the classroom and at home with equal ease. You can observe substances as they change between solid, liquid and gaseous states without expensive lab equipment or advanced scientific knowledge. The demonstrations allow students to become involved, and the activities are quite safe. A predictive element can be added to increase the challenge for the students and retention of the material.
Liquid to Solid
A water phase change experiment from liquid to solid is easy to perform and offers simple variations to study the results. Pure water can be frozen once, then mixed with salt, sugar and Kool-Aid in subsequent trials to see what impacts, if any, these substances have on the freezing rate. The same container should be used for each as a quality control. Try using hot water versus cold water to see if the old myth about "hot water freezing faster than cold water" is true.
Freeze milk, window cleaner and other common items to see if each of these items will freeze and at what rate compared to water. Use a soldering iron to melt solder and then observe how fast it solidifies. Involving the students in the possible reasons for the very fast "freeze time" will help them understand the relationship between a material's freezing point, room temperature and freeze time.
Solid to Liquid
Sugar can be easily melted in a typical saucepan or double boiler. Melting sugar will show the students how some phase changes are not easily reversible. The molecules of the sugar are changed by heating and one cannot turn it back into the powder form.
Water is a great source for a simple experiment where ice is placed into a pan with the heat set on low. Time how long the ice takes to melt, and then repeat the experiment at different temperatures. Perhaps you can have the students predict the melt time on "high" after timing the low and medium results, or graph the results for each test to help in predicting.
Liquid to Gas
If water is heated to 212 degrees Fahrenheit, it will change from a liquid to a gas. If it's boiled in an open container, the liquid water will gradually disappear into the air as a gas. If you boil away a 1/4 cup of water on "high," then you might invite prediction as to how long twice as much water will take and so forth. Try adding other liquids such as soy sauce into the water, keeping the total amount of liquid the same. Does it affect the time of liquid to gas phase change?
Heating cooking oil on high heat for 20 minutes and then re-measuring it will demonstrate how the higher boiling point of the oil prevents much from changing to a gas on the stove at the temperature specified. A comparison between water loss and oil loss during the experiment should help illustrate the effect of boiling point on phase change from liquid to gas.
Gas to Liquid
Water again offers a simple but visual phase change when going from a gas to a liquid. Filling a cup with ice and water and placing it on a non-porous surface at room temperature will yield a classic "ring" around the base in a few minutes. Have the students guess where the water came from, and if there is a relationship between the temperature of the glass and the rate of condensation.
Sublimation
Sublimation is when a phase is "skipped" and a material goes directly from solid to gas or vice-verse. Get some dry ice from a store and place it in an insulated container on a table. Observe it slowly disappearing without any liquid visible.
A less exotic demonstration can be performed with ordinary ice cubes. Weigh a bowl with some ice cubes inside, place in the freezer for a week and re-weigh. The bowl and cubes will weigh less because some of the ice will have sublimated into gas inside the dry freezer environment.
Chemical Reactions
Substances can combine to release gases from liquids and solids as they react with each other or change temperature on their own. A combination of vinegar and baking soda will create a chemical change to release gas bubbles of carbon dioxide. Shaking a transparent bottle of cola and carefully unscrewing the cap (do this outdoors) will demonstrate the gas, which was dissolved in the liquid at colder temperatures, escaping. Be careful as this can be a messy demonstration.
Tags: from liquid, phase change, boiling point, change from, change from liquid, cold water
