This basic experiment is useful to students just starting their experiments with water to see how it responds in various circumstances. The student fills a plastic container to the top with water, puts a lid on it and then places it in the freezer. The student should leave the container in the freezer for at least eight hours. After the appropriate amount of time, the student has to remove the cup from the freezer--he will note first that the water has frozen and second, that the freezing effect has pushed the lid up off the top of the container, showing that the volume of the water has expanded.
To show that water is denser as a liquid than as a solid, the student must fill a cup with water and pour in some cooking oil. After the cooking oil rises to the top and the two fluids separate fully, the student must put the cup into the freezer and leave it for eight hours or overnight. After the chosen amount of time has passed, the student will find that the oil is now at the bottom of the cup and the frozen, less dense, water is on top.
The Mpemba effect states that water changes faster from its liquid state to its solid state when the water is hot. To test this effect, the student has to try freezing multiple cups of water with different temperatures. Since there are multiple factors in this experiment, it is important to keep the conditions the same: The cups should all go into the same freezer, should contain the same amount of water and should all be made of the same material (for instance, a paper drinking cup or a plastic cup). Following these instructions, the student should place water of varying starting temperatures into the cups and put them all in the freezer. He has to then check periodically to see which ones are freezing fastest.
In this experiment, a student will learn why ocean water rarely freezes over but rivers, lakes and ponds freeze as expected. The student should start with two cups of the same material and the same size. She should add the same amount of fresh water at the same temperature to each cup, adding 2 tablespoons of salt to one cup. She then puts both cups into the freezer and lets them stand for eight hours. When the time has passed, the student should find that the fresh water cup is frozen, but the salt water cup is still in liquid form, even though its temperature is below 32 degrees Fahrenheit.