Chemical Properties of Base

These notes are based on the chapter Acids Bases and Salts from NCERT book based on CBSE syllabus.

Types of base
Reaction of base with metal
Reaction of base with metal oxide

What is base?

Base is a substance which is bitter in taste and feels soapy on touch, and turns red litmus paper to blue.

Sodium hydroxide (caustic soda), calcium hydroxide, sodium carbonate (washing soda), lime (Calcium oxide), potassium hydroxide (caustic potash), etc. are examples of base.

Types of Base

Base can be divided in two types – Water soluble and water insoluble.

The ionic salt of alkali and alkaline earth metals are soluble in water. These are also known as alkali. For example: sodium hydroxide, magnesium hydroxide, calcium hydroxide, etc. Alkali is considered as strong base.

Reaction of Base with Metals

When alkali (base) reacts with metal, it produces salt and hydrogen gas.

Alkali + Metal ⇨ Salt + Hydrogen

Reaction of sodium hydroxide with zinc

Example 1: Sodium hydroxide gives hydrogen gas and sodium zincate when reacts with zinc metal.

2NaOH + Zn ⇨ Na₂ZnO₂ + H₂

Reaction of sodium hydroxide with aluminium

Example 2: Sodium aluminate and hydrogen gas are formed when sodium hydroxide reacts with aluminium metal.

2NaOH + 2Al + 2H₂O ⇨ 2NaAlO₂ + 2H₂

Reaction of base with oxides of non-metals

Non-metal oxides are acidic in nature. For example; carbon dioxide is a non-metal oxide. When carbon dioxide is dissolved in water it produces carbonic acid.

Therefore, when a base reacts with non-metal oxide both neutralize each other resulting production of salt and water.

Base + Non-metal oxide ⇨ Salt + Water

Reaction of sodium hydroxide with carbon dioxide

Example 1: Sodium hydroxide gives sodium carbonate and water when it reacts with carbon dioxide.

2NaOH + CO₂ ⇨ Na₂CO₃ + H₂O

Reaction of calcium hydroxide with carbon dioxide

Example 2: Calcium hydroxide gives calcium carbonate and water when it reacts with carbon dioxide.

Ca(OH)₂ + CO₂ ⇨ CaCO₃ + H₂O

General Properties of Base

Concentrated or strong bases are caustic on organic matter and react violently with acidic substances. Caustic means corroding in nature.
Bases in aqueous solutions or molten bases dissociate in ions and conduct electricity.
Bases turn red litmus paper blue, phenolphthalein pink, keep bromothymol blue in its natural colour of blue, and turn methyl orange-yellow.
The pH of a basic solution at standard conditions is greater than seven.
Bases are bitter in taste and feel soapy on touch.