Wondrous Water
By John Cowens

Online Extra: Hot Water vs. Cold Water

Today, we know the ancient Greeks were wrong about Earth's four basic elements being water, air, earth and fire. There are actually more than 90! We also know that water is composed of two elements – oxygen and hydrogen. It's not difficult to make water out of oxygen and hydrogen; we do it frequently. Whenever a substance containing hydrogen is burned, water is formed. At first, it's in the form of vapor. When the vapor cools, it turns into water. The flame of a gas stove, burning candles and automobiles (to mention a few) are producers of water.

Water is usually so commonplace that we think little about it until it becomes scarce. When wells and springs dry up, or the supply is temporarily shut off for repairs to pipes or pumps, we suddenly become unusually thirsty. No life can exist without water. We can live longer without food than water. Water is the most important compound on earth.

Why we need water
When we are in good health our bodies contain a large amount of water. In the tissues of an adult there are about 10 gallons. Three to 10 quarts of this water must be replaced every day. We don't usually drink that amount of water because we get part of our supply from our food. When foods reach the dining table they are almost 75% water; the water may be hidden but it's there. About 75% of a ripe potato is water and about 80% can be found in an apple or fish.

Chemists use more water than any other compound. Most chemical plants are located where water is plentiful and inexpensive. One reason is that few chemical changes can take place without water. Water is also useful in a chemical plant for washing away waste substances.

What's the solution?
Water is important because it forms solutions with many substances. While there is nothing dazzling about this experiment, it has an important purpose. It assists in explaining the solutions that chemists make from water and other liquids. Although chemists use solutions, so do you. You have made solutions many times, probably without realizing it. Whenever you stir sugar in a glass of iced tea or lemonade, you've made a solution. Whenever you drink water, your body will use it to make solutions.

Materials:

• table salt


• sand


• bowl or pan


• glass tumbler


• teaspoon


• water

Procedures:
I recommend using clean building sand for this experiment. You can wash sand if you put a handful in a pan and let water from a faucet run over it until the overspill is clear.

1. Put a teaspoonful of clean sand in a tumbler full of clear water.
2. Stir for a moment.
3. When you stop stirring, the sand will settle to the bottom of the tumbler. You can see it there. It has not been altered in any way. Sand does not dissolve in water. This is not a solution.
4. Add a teaspoonful of table salt (iodized salt used to improve the flavor of food, not sea salt) to the sand and water.
5. Stir for a moment.
6. The salt will dissolve. This time you have made a solution. Although the salt is invisible, it is still present. If you put a drop of the solution on your tongue, you can taste the unseen salt.

Since salt dissolves in water, a chemist would say that it is soluble in water. Because sand does not dissolve in water, sand is insoluble in water.

This experiment brought water to our attention in its role as a solvent. Water is the most plentiful and most useful solvent. Even though it does not dissolve everything, it does dissolve more substances than any other fluid known. Best of all, this most useful solvent is provided by nature.

Which is the best solvent?
Substances usually dissolve more quickly in hot solvents than in cold solvents. Perhaps you've noticed that sugar dissolves more quickly in a cup of hot tea than it does in a glass of iced tea.

Materials:

• two cups


• two spoons


• two lumps of cane sugar


• boiling water


• cold water

Procedures:
This experiment is a race between two lumps of sugar.

1. Fill one of the cups almost full of boiling water.
2. Put the same amount of cold water in the other cup.
3. Choose two lumps of sugar of the same size and drop one in each cup at the same time.
4. Stir the contents of both cups at the same time. The sugar lump in the hot water will dissolve faster than the one in the cold water.

Hot water will dissolve more cane sugar than will an equal amount of cold water. This is not true of table salt. Practically the same amount of salt dissolves in cold water as in hot water.

I hope your students enjoy these experiments as much as mine have. Good luck staying dry!

Online Extra: Hot Water vs. Cold Water

John Cowens teaches sixth grade at Fleming Middle School in Grants Pass, OR.

January, 2007 Volume 37, Number 4