5SO\(_2\)(g) + 2KMnO\(_4\)(aq) + 2H\(_2\)O(l) → K\(_2\)SO\(_4\) + 2MnSO\(_4\)(aq) + 2H\(_2\)SO\(_4\)(aq)
In the reaction above, the products give a
When sulphur dioxide (SO₂) reacts with an acidified solution of potassium permanganate (KMnO₄), the initially purple solution turns colourless. The reason is because the reaction between SO₂ and KMnO₄ is a redox (reduction-oxidation) reaction. SO₂ acts as a reducing agent, meaning it causes the reduction of another substance (KMnO₄), While the permanganate ion (MnO₄⁻) in KMnO₄ is reduced to manganese(II) ions (Mn²⁺), which are colourless.
SO₂ is oxidized to sulphate ions (SO₄²⁻), which are also colourless. So, the purple colour of KMnO₄ is due to the permanganate ion, and when this ion is reduced, the solution becomes colourless.
There is an explanation video available below.
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