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Question

Which one of the following reactions is not associated with the Solvay process of manufacture of sodium carbonate?


A
NaCl+NH4HCO3NaHCO3+NH4Cl
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B
2NaOH+CO2Na2CO3+H2O
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C
2NaHCO3Na2CO3+H2O+CO2
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D
NH3+H2O+CO2NH4HCO3
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Solution

The correct option is A 2NaOH+CO2Na2CO3+H2O
In the first step, CO2 is made to pass through a concentrated aqueous solution of NaCl and NH3.
NaCl+CO2+NH3+H2ONaHCO3+NH4Cl  - (1)

The bicarbonate precipitates out and because the solution is already basic it is less soluble than NaCl
The CO2 needed for teh above reaction is derived from calcination of limestone:

CaCO3CO2+CaO - (2)

The NH4Cl from the first reaction (1) is made to react with the CaO obtained from calcination (2):

2NH4Cl+CaO2NH3+CaCl2+H2O

Observe the products of this reaction - particularly CaCl2 and NH3
The former is a useful by-product while ammonia is recycled or fed back into the very first reaction at the top.

The sodium bicarbonate NaHCO3 precipitated out initially from the first reaction is then converted to the final product, 
sodium carbonate Na2CO3, by calcination (160–230 °C), producing water and carbon dioxide as by-products:

2NaHCO3Na2CO3+H2O+CO2

The carbon dioxide from step (IV) is recovered for re-use in step (I).

Chemistry

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