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Question
Identify the gas evolved and give the chemical test in the following case:
Dilute hydrochloric acid reacts with sodium sulphite.
Solution
Gas Evolved:
When dilute hydrochloric acid reacts with sodium sulphite, the gas evolved is sulphur dioxide.
Reaction:
\[\ce{Na2SO3 + 2HCl -> 2NaCl + H2O + SO2 ^}\]
Chemical Test for sulphur dioxide: Pass the gas through an acidified potassium dichromate \[\ce{(K2Cr2O7}\]) solution.
Observation: The solution changes color from orange to green due to the reduction of chromium from \[\ce{Cr^{6+}}\] to \[\ce{Cr^{3+}}\].
\[\ce{SO2 + H2O + K2Cr2O7 + H2SO4 -> Cr2(SO4)3 + K2SO4 + H2O}\]
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