Question

Which of the following method(s) is/are used in preparing a base?

• A. Burning of metal in air
• B. Adding water to a metal oxide.
• C. Reaction between an acid and base
• D. Heating metal carbonates

Answer 1

Answer: (B), (C)

The correct options are
B

Adding water to a metal oxide.

C

Reaction between an acid and base

When metal oxides react with water, they form bases by associating with hydroxyl ion present in water. Basic oxides can be formed by direct combination of metals with oxygen. For e.g.,
CaO + $H_{2}O$ $\to$ $Ca(OH{)}_2$

On heating metal carbonates, the metal carbonate undergoes thermal decomposition to form a metal oxide and carbon dioxide gas. Hence no base is formed. For eg,

$CaC{O}_3\to CaO+C{O}_2$

On adding water to a reactive metal, they form a base and hydrogen gas. For eg,

$2Na+2H_{2}O\to 2NaOH+H_2$

By burning metal in air, metal reacts with oxygen to form a metal oxide. For eg,

$2Mg+O_2\to 2MgO$