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Question
What do you observe when dilute sulphuric acid is added to the following:
Sodium Sulphide
Solution
The reaction between dil. sulphuric acid and sodium sulphite occurs in two steps and is a double replacement reaction.
In the first step, sulphuric acid reacts with sodium sulphide to give sodium sulphate and sulphurous acid.
\[\ce{H2SO4 + Na2SO3 -> Na2SO4 + H2SO3}\]
In the second step, sulphurous acid, which is highly unstable decomposes spontaneously into sulphur dioxide and water.
\[\ce{H2SO3 -> SO2 + H2O}\]
Thus, the overall reaction is written as:
\[\ce{H2SO4 + NaSO3 ->Na2SO4 + SO2 ++ H2O}\]
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