Question

Which of the following is a double replacement reaction? Ca(OH)2 + H2SO4 → CaSO4 + 2H2O CH4 + 2O2 → CO2 + 2H2O 8Fe + S8 → 8FeS Zn + H2SO4 → ZnSO4 + H2

Answer 1

That would be the first option Ca(OH)2 + H2SO4  → CaSO4 + 2H2O.

The Ca replaces the H2 in H2SO4,  and the  H2 replaces the Ca is Ca(OH)2.

Answer 2

Answer: Option (a) is the correct answer.

Explanation:

A chemical reaction in which there occurs exchange of two ions between two different compounds is known as a double replacement reaction.

For example, $Ca(OH)_{2} + H_{2}SO_{4} \rightarrow CaSO_{4} + 2H_{2}O$

Here, $OH^{-}$ ions of $CaOH_{2}$ is replaced by $SO^{21}_{4}$ ions of sulfuric acid and  $SO_{4}$ of sulfuric acid is replaced by $OH^{-}$ ions of $CaOH_{2}$.

When two atoms combine together to form a compound then it is known as synthesis reaction.

When a compound reacts with oxygen to give carbondioxide and water then it is known as combustion reaction.

When a metal is treated with an acid to yield hydrogen gas then it is known as single replacement reaction.

Therefore, we can conclude that $Ca(OH)_{2} + H_{2}SO_{4} \rightarrow CaSO_{4} + 2H_{2}O$  is a double replacement reaction.