Question

A sample of air turns lime water milky and also turns acidified potassium dichromate green in aqueous solution has low pH. This is due to the presence of pollutants.

Options

• CO₂

• SO₂

• Both CO₂ and SO₂

• None of these

Answer 1

SO₂ 

Explanation:

SO₂ turns lime water milky.

SO₂ in aqueous solution gives \[\ce{H2SO3}\].

\[\ce{H2SO3 <=> H+ + HSO^-_3}\]

CO₂ also turns lime water milky.

CO₂ in aqueous solution gives \[\ce{H2CO3}\].

\[\ce{H2CO3 <=> H+ + HCO^-_3}\]

\[\ce{H2SO3}\] is stronger acid than \[\ce{H2CO3}\]. Thus, ionisation of \[\ce{H2SO3}\] is larger than \[\ce{H2CO3}\]. Thus, pH of \[\ce{H2SO3}\] is lower than that of \[\ce{H2SO2}\].