Name the gas evolved in each of the following cases:
(i) Action of heat on magnesium carbonate
(ii) Action of heat on calcium nitrate
(iii) Addition of dilute sulphuric acid to sodium sulphite
(iv) Action of heat on washing soda
(v) Action of dilute hydrochloric acid on zinc sulphide
Answers
Gases evolved in the given reactions :
(i) Action of heat on magnesium carbonate evolves carbon dioxide gas.
MgCO₃ + ∆ → MgO + CO₂
(ii) Action of heat on calcium nitrate produces a reddish-brown gas of nitrogen dioxide, along with colourless oxygen.
2Ca(NO₃)₂ + ∆ → 2CaO + 4NO₂ + O₂
(iii) Addition of dilute sulphuric acid to sodium sulphite produces a pungent odour of sulphur dioxide gas.
Na₂S₂O₃ + dil. H₂SO₄ → Na₂SO₄ + H₂O + SO₂
(iv) Action of heat on washing soda produces water vapour.
The chemical formula of washing soda is Na₂CO₃.10H₂O .
Na₂CO₃.10H₂O + ∆ → Na₂CO₃ + 10H₂O
(v) Action of dilute hydrochloric acid on zinc sulphide evolves hydrogen suplhide gas with a smell of rotten eggs.
ZnS + 2dil. HCl → ZnCl₂ + H₂S
Gases evolved in each of the reaction are:--
(i)Action of heat on magnesium carbonate is magnesium carbonate decomposes on heating and the evolved gas is carbon dioxide. The reaction is--- MgCO3+ heat------>MgO(s) + CO2(g).
(ii)Action of heat on calcium nitrate is that the compound decomposes to calcium oxide along with reddish brown gas known as nitrogen dioxide along with oxygen gas. The reaction is :--
2Ca(NO3)2 + heat-------->2CaO + 4NO2 + O2
(iii)Addition of dilute sulphuric acid on sodium sulphite is two step reaction, in step one sulphuric acid reacts with sodium sulphite to give sodium sulphate and sulphurous acid and in second step the acid decomposes to give water and sulphur dioxide gas is evolved. The reaction is:--
H2SO4(dilute) + Na2SO3--------->Na2SO4 + SO2 + H2O
(iv)Action of heat on washing soda is first the water of crystallization is removed then the dry Na2CO3 is further heated to give sodium oxide and CO2 as gaseous product. The reaction is:--
Na2CO3.10H2O + heat---------->Na2O + CO2 + 10H2O
(v)Action of dilute hydrochloric acid on zinc sulphide is we get black precipitate of zinc chloride and hydrogen sulphide gas is evolved which is pungent smelling gas. The reaction is:--
ZnS + HCl(dilute)---------->ZnCl2 + H2S