Preparation of Salt cake : (i) The anhydrous sodium sulphate (salt cake) is obtained as a by-product in the manufacture of hydrochloric acid.
(ii) Salt cake is also produced during the manufacture of sodium carbonate when `NaCl` is heated w'ith `H_2SO_4`.
(iii) Now-a-days, it is manufactured by heating `NaCl` with sod. bisulphate (nitre cake). Nitre cake is obtained by the action of `H_2SO_4` on sodium nitrate (Chile saltpetre).
`undersettext(Chile saltpeter )(NaNO_3) + H_2SO_4 -> undersettext(Nitre cake)(NaHSO_4) + HNO_3`
`undersettext(Nitre cake)(NaCl) + NaHSO_4 -> undersettext(Salt cake)(Na_2SO_4) + HCl uparrow`
Preparation of Glauber's salt, `Na_2SO_4.10H_2O :` The salt cake `(Na_2SO_4)` is dissolved in water and the solution is subjected for crystallization. Below `32-C`, the decahydrate salt crystallises out from the aqueous solution. Above `32-C` the anhydrous salt separates. Saturated solution of the decahydrate, on cooling below `12-C`, gives crystals of heptahydrare.
`text(Properties)` :
(i) The decahydrate effloresces in dry air forming the anhydrous salt. It is a crystalline solid, soluble in water.
(ii) On treatment with lead, barium or strontium salts, it forms the corresponding insoluble sulphate, e.g.
`Pb(NO_3)_2 + Na_2SO_4 -> PbSO_4 downarrow + 2NaNO_3`
(iii) When a solution having equivalent quantity of anhydrous `Na_2SO_4` and conc. `H_2SO_4` is cooled, prismatic crystals of sodium bisulphate (sodium hydrogen sulphate, `NaHSO_4` ) are formed.
`Na_2 SO_4 +H_2SO_4 -> 2NaHSO_4`
(iv) On heating with carbon it is reduced to sod. sulphide.
`Na_2SO_4 + 4C -> Na_2S +4 CO`
`text(Uses)` : Sodium sulphate is used :
(i) in the manufacture of craft paper (brown paper for wrapping, etc.) and paper board,
(ii) in the manufacture of window glass,
(iii) as mild laxative (in medicine) and
(iv) in the preparation of `Na_2S, Na_2S_2O_3` and `NaHSO_4`. sod. bisulphate is an acidic salt in solution and can be used in place of sulphuric acid. For example, `Al_2O_3`, which is not attacked by `H_2SO_4`, may be converted into sulphate when fused with sodium hydrogen sulphate.
`Al_2O_3 + 6NaHSO_4 -> Al_2(SO_4)_3 + 3Na_2SO_4 + 3H_2O`
Preparation of Salt cake : (i) The anhydrous sodium sulphate (salt cake) is obtained as a by-product in the manufacture of hydrochloric acid.
(ii) Salt cake is also produced during the manufacture of sodium carbonate when `NaCl` is heated w'ith `H_2SO_4`.
(iii) Now-a-days, it is manufactured by heating `NaCl` with sod. bisulphate (nitre cake). Nitre cake is obtained by the action of `H_2SO_4` on sodium nitrate (Chile saltpetre).
`undersettext(Chile saltpeter )(NaNO_3) + H_2SO_4 -> undersettext(Nitre cake)(NaHSO_4) + HNO_3`
`undersettext(Nitre cake)(NaCl) + NaHSO_4 -> undersettext(Salt cake)(Na_2SO_4) + HCl uparrow`
Preparation of Glauber's salt, `Na_2SO_4.10H_2O :` The salt cake `(Na_2SO_4)` is dissolved in water and the solution is subjected for crystallization. Below `32-C`, the decahydrate salt crystallises out from the aqueous solution. Above `32-C` the anhydrous salt separates. Saturated solution of the decahydrate, on cooling below `12-C`, gives crystals of heptahydrare.
`text(Properties)` :
(i) The decahydrate effloresces in dry air forming the anhydrous salt. It is a crystalline solid, soluble in water.
(ii) On treatment with lead, barium or strontium salts, it forms the corresponding insoluble sulphate, e.g.
`Pb(NO_3)_2 + Na_2SO_4 -> PbSO_4 downarrow + 2NaNO_3`
(iii) When a solution having equivalent quantity of anhydrous `Na_2SO_4` and conc. `H_2SO_4` is cooled, prismatic crystals of sodium bisulphate (sodium hydrogen sulphate, `NaHSO_4` ) are formed.
`Na_2 SO_4 +H_2SO_4 -> 2NaHSO_4`
(iv) On heating with carbon it is reduced to sod. sulphide.
`Na_2SO_4 + 4C -> Na_2S +4 CO`
`text(Uses)` : Sodium sulphate is used :
(i) in the manufacture of craft paper (brown paper for wrapping, etc.) and paper board,
(ii) in the manufacture of window glass,
(iii) as mild laxative (in medicine) and
(iv) in the preparation of `Na_2S, Na_2S_2O_3` and `NaHSO_4`. sod. bisulphate is an acidic salt in solution and can be used in place of sulphuric acid. For example, `Al_2O_3`, which is not attacked by `H_2SO_4`, may be converted into sulphate when fused with sodium hydrogen sulphate.
`Al_2O_3 + 6NaHSO_4 -> Al_2(SO_4)_3 + 3Na_2SO_4 + 3H_2O`