WAEC - Chemistry (2022 - No. 14)
A colourless gas with a pungent smell is evolved when dilute hydrochloric acid is added to a sample of a salt. The gas evolved could turn
acidified K\(_{2}\)Cr\(_{2}\)O\(_{7}\) solution colourless
acidified KMnO\(_{4}\) solution colourless
Fe(NO\(_{3}\))\(_{2}\) solution green
Pb(NO\(_{3}\))\(_{2}\) paper black
Explanation
If the potassium manganate(VII) solution is acidified with dilute sulfuric acid, the purple solution becomes colourless.
The salt that reacts with dilute hydrochloric acid to produce a pungent smelling gas which decolourizes acidified purple potassium tetraoxomanganate (VII) solution is Na\(_2\)SO\(_3\)
Na\(_2\)SO\(_3\)(s) + HCl(aq) → NaCl(aq) + H\(_2\)O(l) + SO\(_2\)(g)
When SO\(_2\) gas which is colourless with a pungent smell, reacts with acidified KMnO\(_4\), it becomes decolorized from purple colour.
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