(a) Sodium sulphite and sodium carbonate :
On adding dilute sulphuric acid to sodium sulphite and warming, a colourless gas with suffocating smell of burning sulphur is evolved. The evolved gas turns lime water milky and changes the colour of acidified K2Cr2O7 solution from orange to green suggesting that it is SO2.
Na2SO3 + H2SO4 (dil.) ⟶ Na2SO4 + H2O + SO2↑
On adding dilute sulphuric acid to sodium carbonate and warming, a colourless gas is evolved with brisk effervescence. The evolved gas extinguishes a burning wooden splinter and turns lime water milky but has no effect on acidified K2Cr2O7 solution suggesting that it is CO2.
Na2CO3 + H2SO4 (dil.) ⟶ Na2SO4 + H2O + CO2↑
(b) Copper and magnesium :
Magnesium on reaction with dil. sulphuric acid produces a colourless, odourless gas with brisk effervescence. The gas evolved is hydrogen as it burns with a pale blue flame producing a pop sound.
Copper does not react with dil. sulphuric acid liberating hydrogen as it is lower in metal reactivity series than hydrogen.
(c) Sodium sulphide and sodium sulphite :
When dil. sulphuric acid is added to sodium sulphide and heated, hydrogen sulphide gas is evolved which has the smell of rotten eggs.
Na2S + H2SO4 ⟶ Na2SO4 + H2S ↑
On adding dilute sulphuric acid to sodium sulphite and warming, a colourless gas with suffocating smell of burning sulphur is evolved. The evolved gas turns lime water milky and changes the colour of acidified K2Cr2O7 solution from orange to green suggesting that it is SO2.
Na2SO3 + H2SO4 (dil.) ⟶ Na2SO4 + H2O + SO2↑