Question
Explain the similarity and difference in two events, namely adding $NaOH$ to water and adding $CaO$ to water.
✓
Answer
Similarity: Both $NaOH$ and $CaO$, when dissolved separately in water, solid $NaOH$ dissolves releasing heat, resulting in rise in temperature. This reaction is exothermic reaction. When solid $CaO$ dissolves in water, $Ca ( OH )_2$ is formed, large amount of heat is evolved. This reaction is also exothermic reaction. Both reactions are combination reactions and single product is obtained.
$
\begin{aligned}
& NaOH _{(s)}+ H _2 O \rightarrow NaOH _{( aq )}+\text { Heat } \\
& CaO _{( s )}+ H _2 O \rightarrow Ca ( OH )_{2( aq )}+\text { Heat }
\end{aligned}
$
Difference:
1. Aqueous solution of $NaOH$ is considered as a strong alkali.
2. Aqueous solution of $Ca ( OH )_2$ is considered as a weak alkali.
$
\begin{aligned}
& NaOH _{(s)}+ H _2 O \rightarrow NaOH _{( aq )}+\text { Heat } \\
& CaO _{( s )}+ H _2 O \rightarrow Ca ( OH )_{2( aq )}+\text { Heat }
\end{aligned}
$
Difference:
1. Aqueous solution of $NaOH$ is considered as a strong alkali.
2. Aqueous solution of $Ca ( OH )_2$ is considered as a weak alkali.
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