Acids, Bases and Salts: Properties and Reactions

What are Acids, Bases and Salts?

An acid is a substance that dissolves in water to produce hydrogen ions (H+), tastes sour, and turns blue litmus paper red. A base is a substance that produces hydroxide ions (OH-) in water, feels soapy, and turns red litmus paper blue; a base that dissolves in water is called an alkali. A salt is the compound formed, along with water, when an acid reacts with a base.

Properties of Acids

• Sour taste (e.g. citric acid in lemons).
• Turn blue litmus paper red.
• React with reactive metals to produce hydrogen gas.
• React with carbonates to produce carbon dioxide gas.
• Have a pH value less than 7.

Properties of Bases

• Bitter taste and slippery/soapy feel.
• Turn red litmus paper blue.
• React with acids to form a salt and water (neutralisation).
• Have a pH value greater than 7.

Neutralisation and Salt Formation

When an acid reacts with a base, they neutralise each other, forming a salt and water: Acid + Base → Salt + Water. For example, hydrochloric acid reacting with sodium hydroxide produces sodium chloride (common salt) and water.

The pH Scale

The pH scale runs from 0 to 14 and measures how acidic or alkaline a substance is: values below 7 are acidic, 7 is neutral (pure water), and above 7 is alkaline/basic. Indicators such as litmus paper or universal indicator solution are used to test pH.

Everyday Uses

Acids are used in car batteries, food preservation and cleaning; bases are used in soap making, antacids for indigestion, and in agriculture to reduce soil acidity; salts such as sodium chloride are essential for cooking and food preservation, and many other salts are used as fertilizers.