Question

The normal rain water is slightly acidic and its $pH$ value is $5.6$ because of which one of the following ?

• A. $CO _2+ H _2 O \rightarrow H _2 CO _3$
• B. $N _2 O _5+ H _2 O \rightarrow 2 HNO _3$
• C. $2 SO _2+ O _2+2 H _2 O \rightarrow 2 H _2 SO _4$
• D. $4 NO _2+ O _2+2 H _2 O \rightarrow 4 HNO _3$

Answer 1

Answer: (A)

We are aware that normally rain water has a $pH$ of $5.6$ due to the presence of $H ^{+}$ions formed by the reactions of rain water with carbon dioxide present in the atmosphere.
$ H _2 O ( l )+ CO _2( g ) \leftrightharpoons H _2 CO _3( aq )$
$H _2 CO _3( aq ) \leftrightharpoons H ^{+}( aq )+ HCO _3^{-}( aq ) $