Mild acids, such as acetic acid in vinegar, taste sour.
Strong acids, such as sulphuric acid, are highly corrosive. They can dissolve metals.
Acids are solutions that are made when certain substances containing hydrogen dissolve in water.
Hydrogen atoms have a single electron. When acid-making substances dissolve in water, the hydrogen atoms lose their electron and become positively charged ions. Ions are atoms that have gained or lost electrons.
The strength of an acid depends on how many hydrogen ions form.
The opposite of an acid is a base. Weak bases such as baking powder taste bitter and feel soapy. Strong bases such as caustic soda are corrosive.
A base that dissolves in water is called an alkali. Alkalis contain negatively charged ions – typically ions of hydrogen and oxygen, called hydroxide ions.
When you add an acid to an alkali, both are neutralized. The acid and alkali react together forming water and a salt.
Chemists use indicators such as litmus paper to test for acidity. Acids turn litmus paper red. Alkalis turn it blue. The strength of an acid may be measured on the pH scale. The strong acid (laboratory hydrochloric) has a pH of 1. The strongest alkali has a pH of 14. Pure water has a pH of about 7 and is neutral – neither acid nor alkali.