NH3 + H2O + CO2 → NH4HCO3
NaCl + NH4HCO3-→ NaHCO3 + NH4Cl
2NaHCO3 → Na2CO3 + H2O + CO2
(i) Anhydrous Na2CO3 is called as soda ash, which does not decompose on heating but melts at 852°C
(ii) It forms number of hydrates.
Na2CO3. H2O------>. Crystal carbonate <-------Na2CO3 + moisture in air
Na2CO3.10H2O ----> Washing soda
(iii) Na2CO3 absorbs CO2 yielding sparingly soluble sodium bicarbonate which can be calcined at 250° to get pure sodium carbonate.
(iv) It dissolved in acid with effervescence of CO2 and causticised by lime to give caustic soda.
Na2CO3 + HCl > 2NaCl + H2O + CO2
Na2CO3 + Ca(OH)2 2NaOH + CaCO3
Uses : It is widely used in glass making as smelter .
Potassium Carbonate :
By Leblanc process, it can be prepared but by Solvay process it cannot be prepared because KHCO3 is soluble in water.
Properties: It resembles with Na2CO3, m.p. is 900ºC but a mixture of Na2CO3 and K2CO3 melts at 712ºC.
Uses : It is used in glass manufacturing.
Potassium Carbonate :
It occurs in nature as marble, limestone, chalk, coral, calcite etc. It is prepared by dissolving marble or limestone in HCl and removing iron and aluminium present, by precipitating with NH3 and then adding (NH4)2CO3 to the solution.
CaCl2 + (NH4)2CO3 ------>. CaCO3 + 2NH4Cl
1. It dissociates above 1000°C as follows:
CaCO3----->CaO + CO2
2. It dissolves in water containing CO2 forming Ca(HCO3)2 but is precipitated from the solution by boiling.
Magnesium carbonate :
It occurs in nature as magnesite, isomorphous with calcite. It is obtained as a white precipitated sodium bicarbonate to a solution of a magnesium salt; but only basic carbonate, called magnesia alba, having the approximate composition MgCO3.Mg(OH)2. 3H2O is precipitated.
Properties : Same with CaCO3.
Sodium bicarbonates :
Preparation : By absorption of CO2 in Na2CO3 solution.
Uses : It is used in medicine and as baking powder.
Preparation : Same NaHCO3
Properties : Same with NaHCO3
But, it is more alkaline and more soluble in water compared to NaHCO3.
Magnesium bicarbonate :
Sodium Chloride : Prepared from brine containing 25% NaCl.
(i) It is non-hygroscopic but the presence of MgCl2 in common salt renders it hygroscopic.
(ii) It is used to prepare freezing mixture in laboratory [Ice-common salt mixture is called freezing mixture and temperature goes down to – 23ºC.]
(iii) For melting ice and snow on road.
Potassium Chloride : It is also occurs in nature as sylvyne (KCl) or carnalite (2KCl . MgCl2 6H2O)
Uses : It is used as fertiliser.
Magnesium Chloride :
Preparation : By dissolving MgCO3 in dil. HCl.
MgCO3 + 2HCl → MgCl2 + H2O + CO2
(i) It crystallises as hexahydrate. MgCl2. 6H2O
(ii) It is deliquescent solid.
(iii) This hydrate undergoes hydrolysis as follows:
* Hence, Anhy. MgCl2 cannot be prepared by heating this hydrate.
* * Because of this formation of HCl, Sea water cannot be used in marine boilers which corrodes the iron body.
(iv) Anhydrous MgCl2 can be prepared by heating a double salt like. MgCl2 . NH4Cl . 6H2O as follows:
Sorel Cement: It is a mixture of MgO and MgCl2 (paste like) which set to hard mass on standing. This is used in dental filling, flooring etc.
Calcium chloroide :
(i) It is the by-product in solvay process.
(ii) It may also be prepared by dissolving the carbonate in HCl .
CaCO3 + 2HCl → CaCl2 + H2O + CO2
(i) It is deliquescent crystals.
(ii) It gets hydrolysed like MgCl2 hence anhydrous CaCl2 cannot be prepared.
CaCl2 + H2O CaO + 2HCl
Hence, anhy. CaCl2 is prepared by heating CaCl2.6H2O in a current of HCl (dry)
(iii) Anhy. CaCl2 is used in drying gases and organic compounds but not NH3 or alcohol due to the formation of CaCl2. 8NH3 and CaCl2. 4C2H5OH.
It is formed in the 1st step of Leblanc process by heating common salt with sulphuric acid.
2NaCl + H2SO4 → Na2SO4 + 2HCl
Thus the salt cake formed is crystallised out from its aqueous solution as Na2SO4.10H2O. This called as Glauber's salt.
** One interesting feature of the solubility of Glauber's salt is: when crystallised at below
32.4ºC, then Na2SO4. 10H2O is obtained but above 32.4ºC, Na2SO4 (anhy.) comes out.
Properties : It is reduced to Na2S when fused with carbon.
Na2SO4 + 4C → Na2S + 4CO
Uses : It is used in medicine.
Potassium Sulphate :
It occurs in sulphate of potash beds as schonite K2SO4. MgSO4.6H2O and Kainite, KCl .MgSO4.3H2O from which it is obtained by solution in water and crystallisation. It separates from the solution as anhydrous crystals whereas Na2SO4 comes as decahydrate.
Uses : It is used to prepare alum.
Magnesium Sulphate :
(i) It is obtained by dissolving Kieserite, MgSO4.H2O in boiling water and then crystallising the solution as a heptahydrate. i.e. MgSO4. 7H2O. It is called as Epsom salt.
(ii) It is also obtained by dissolving magnesite in hot dil. H2SO4.
MgCO3 + H2SO4 → MgSO4 + H2O + CO2
(iii) Or by dissolving dolomite (CaCO3, MgCO3) in hot dil. H2SO4 and removing the insoluble CaSO4 by filtration.
(iv) It is isomorphous with FeSO4.7H2O, ZnSO4.7H2O
Calcium Sulphate : It occurs as anhydrite CaSO4 and as the dihydrate CaSO4. 2H2O, gypsum, alabaster or satin-spar.
(ii) Solubility of CaSO4 at first increases upto a certain point and then decreases with rise of temperature.
(iii) Plaster of Paris is used in mould making due to its porous body.