Chemistry
A water insoluble substance A on reacting with dilute H2SO4 releases a gas which turns a paper dipped in acidified potassium dichromate solution green. When the gas is passed through lime water, the solution obtained turns blue litmus red. On bubbling the gas through lime water, it initially became turbid and the turbid nature disappeared when the gas is passed in excess.
(a) Identify the substance 'A'.
(b) Write the chemical equations of the reactions involved.
(c) State the type of reactions that are involved.
Answer
(a) The substance A is sodium sulphite.
(b) The reactions involved are:
SO2 formation
Na2SO3 + H2SO4 ⟶ Na2SO4 + H2O + SO2Reaction with potassium dichromate
K2Cr2O7 + 3SO2 + H2SO4 ⟶ K2SO4 + Cr2(SO4)3 + H2OReaction with lime water
Ca(OH)2 + SO2 ⟶ CaSO3 + H2OExcess SO2
CaSO3 + SO2 + H2O ⟶ Ca(HSO3)2
(c)
SO2 formation - Double displacement reaction
Reaction with potassium dichromate - Redox reaction
Reaction with lime water - Combination reaction
Excess SO2 - Combination reaction
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