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Water

by Ron Kurtus (6 April 2007)

Water is the most abundant and useful of the thousands of compounds known to man. It can be formed through oxidation, reduction and neutralization. Properties of water include being a cleansing agent and being able to cause inactive materials to react with each other, thus speeding up the chemical action. The composition of water can be determined by analysis and synthesis.

Questions you may have include:

• How is water formed?
• What are the chemical properties of water?
• How is the composition of water found?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

Formation of water

Water is formed as one of the products in many chemical reactions:

Direct union of oxygen and hydrogen through burning

Hydrogen plus oxygen yields water: 2H₂ + O₂ → 2H₂O

Oxidation of a compound of hydrogen

Acetylene plus oxygen yields carbon dioxide plus water: 2C₂H₂ + 5O₂ → 4CO₂ + 2H₂O

Reduction of an oxide by hydrogen

Copper oxide plus hydrogen yields copper plus water: CuO + H₂ → Cu + H₂O

Neutralization of the base by an acid

Potassium hydroxide plus hydrochloric acid yields potassium chloride plus water: KOH + HCl → KCl + H₂O

Chemical properties

Water is a principal cleansing agent, because of its ability to dissolve other substances. Because it readily form solutions, water is able to bring together otherwise in active materials and cause them to react with each other much more quickly than in the dry states. Thus, water is one of our most important aids in speeding up chemical action.

Other major properties include:

• Water is an extremely stable compound. Extreme heat is required to break apart water molecules.
• Water or steam will react with various metals, such as sodium, calcium and iron. Typically, parts or all of the hydrogen of the water is replaced by the mental.
• Water can be broken into hydrogen and oxygen gases through the process of electrolysis, which is running electric current through the liquid.
• Water combined with certain metallic oxides or basic and hydrides to form bases.
• Water also combines with certain non-metallic oxides or acid and hydrides to form acids.
• Water reacts with certain salts to form both an acid and a base.
• Water combined with some compounds when they crystallize from a solution forming hydrides.

Many chemical reactions cannot proceed without the presence of some water. For example, a spark applied to a mixture of perfectly dry hydrogen and oxygen no action occurs however, if there is even a minute trace of water present the mixture explodes readily. Similarly, phosphorus does not catch fire in dry air, but it quickly burst into a flame if there is the slightest amount of moisture present.

Finding the composition of water

The composition of a material consists of its chemical formula, which indicates which elements are included in the material and how many of each are in the molecule. Although we already know that water is H₂O, it is good to go through the exercise of finding its composition. The common methods used to find the composition of a material are by analysis and synthesis.

Analysis

Analysis consists of breaking apart a compound into its elements. By using electrolysis, you can break water into hydrogen and oxygen gases. The method will show that there is twice as much volume of hydrogen gas as there is of oxygen gas. Thus, the equation: 2H₂O → 2H₂ + O₂.

Synthesis

The synthesis of water is the process of forming the compound by the direct union of its elements or of other compounds.

The composition of water may be determined through synthesis by volume. This is done by forming a reaction between measured volumes of oxygen and hydrogen. It is seen that two volumes of hydrogen and one volume of oxygen combine to make water with no excess gas left over.

Summary

Water is an abundant and useful compound. It can be formed through oxidation, reduction and neutralization. A major properties of water is that it can cause inactive materials to react with each other. The composition of water can be determined by analysis and synthesis.

Answers to Readers' Questions

Resources

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Mini-quiz to check your understanding

1. How can an acid be used to form water?

2. What happens when iron is exposed to water?

3. What would happen if you burned two parts of hydrogen with two parts of oxygen?

If you got all three correct, you are on your way to becoming a Champion in Chemistry. If you had problems, you had better look over the material again.

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