Facts At Your Fingertips: Matter and materials – Acids and bases
Acids and bases are chemical opposites: acids produce positively charged hydrogen ions and bases produce negatively charged hydroxide ions.
Many acids and bases can be combined to produce useful substances, such as salts and soaps.
Acids
Some powerful acids are very corrosive, which means they can destroy, or “eat through,” other substances.
Weaker acids, such as lemon juice and vinegar, have a strong, sour taste. These are often used to flavor food and can also be found in many household cleaning products.
Bases and alkalis
Strong bases can be as dangerous as strong acids, although a base that destroys other substances is usually known as caustic rather than corrosive.
Sodium hydroxide (caustic soda) can eat through some metals. Sodium bicarbonate, or baking soda, is a weak base, often used in cooking. Some bases are water-soluble and are called alkalis.
Mixing acids and bases
When certain acids and bases are mixed, they can react to produce water and a salt.
Soap is made when a strong base is added to a fatty acid (a building block of fats found in our bodies and food), breaking it down to form a hard or soft soap (depending on the base).
Measuring acids and bases
The strength of acids and bases is measured using the pH (power of hydrogen) scale.
It ranges from zero (strong acid) to 14 (strong base). Pure water is seven on the pH scale, which is neutral—neither acid nor base. The pH of a substance can be measured using a pH indicator such as litmus paper.
The color of the indicator changes according to the pH of the substance.