Question

Sodium salt of an organic acid ‘Produces effervescence with conc. ${{\text{H}} _ {2}} \text{S}{{\text{O}} _ {4}} $. ‘X’ reacts with the acidified aqueous $\text {CAC}{{\text{l}} _ {2}} $ solution to give a white precipitate which decolorizes acidic solution of $\text {MN}{{\text{O}} _ {4}} $‘X’ is:
(a) HCOO Na
(b) $\text{C}{{\text{H}} _ {3}} \text {COONa}$
(c) $\text{N}{{\text{a}} _ {2}} {{\text{C}} _ {2}} {{\text{O}} _ {4}} $
(d) ${{\text{C}} _ {6}} {{\text{H}} _ {5}} \text {COONa}$

Answer 1

Hint: Oxalic acid is compound which when reacted with the concentrated ${{\text{H}} _ {2}} \text{S}{{\text{O}} _ {4}} $ produces the effervescence i.e. There is the evolution of carbon dioxide gas and its salt too on reaction produces the effervescence. Now solve it and find ‘X’.

Complete Solution :
The given data suggests the salt of organic compounds which gives effervescence with conc. sulphuric acid is ‘$\text{N}{{\text{a}}_{2}}{{\text{C}}_{2}}{{\text{O}}_{4}}$’ i.e. sodium oxalate. It is a white crystalline solid and is an organic compound made up of sodium and oxalate ions. Sodium salt oxalate reacts readily with the concentrated sulphuric acid and produces effervescence i.e. the bubbles are formed in the solution due to the evolution of carbon dioxide gas on reaction which tries to escape from the solution. Besides the carbon dioxide gas, carbon monoxide gas is formed which also escapes from the solution. Now, the point is that we should take sodium salt of which organic compound. Always remember that the oxalic acid on reaction with the concentrated sulphuric acid always gives carbon dioxide gas and it is the gas mainly responsible for the effervescence in the solution.
- So , the Sodium salt of an organic acid 'X' is sodium oxalate $\text{N}{{\text{a}}_{2}}{{\text{C}}_{2}}{{\text{O}}_{4}}$ ​which on reaction with the acid i.e. concentrated sulphuric acid gives effervescence of $\text{C}{{\text{O}}_{2}}$ gas . the reaction occurs as:
$N{{a}_{2}}{{C}_{2}}{{\text{O}}_{4}}\text{+}{{\text{H}}_{2}}\text{S}{{\text{O}}_{2}}\to \text{N}{{\text{a}}_{2}}\text{S}{{\text{O}}_{4}}\text{+}{{\text{H}}_{2}}\text{O+CO}\uparrow \text{+C}{{\text{O}}_{2}}\uparrow $
Sodium oxalate
 (X)

when the sodium oxalate is made to react with the acidified aqueous $\text {CAC}{{\text{l}} _ {2}} $ ​ solution, the calcium displaces sodium from the sodium oxalate and gives calcium oxalate precipitates which are white in color and sodium chloride is also formed.
$\text{N}{{\text{a}}_{2}}\text{C}{{\text{O}}_{4}}\text{+Ca C}{{\text{l}}_{2}}\to \text{Ca}{{\text{C}}_{2}}{{\text{O}}_{4}}\downarrow \text{+2NaCl}$
                                Calcium oxalate

when this calcium oxalate is made to react with an acidic solution of $\text {MN}{{\text{O}} _ {4}} $, it decolorizes the solution.
$\text{5}{{\text{C}}_{2}}{{\text{O}}_{4}}\text{+16}{{\text{H}}^{+}}\text{+2MnO}_{4}^{-}\to \text{2M}{{\text{n}}^{2+}}\text{+10C}{{\text{O}}_{2}}\text{+8}{{\text{H}}_{2}}\text{O}$
So, the correct answer is “Option C”.

Note: Be careful while writing all the reactions and balance them properly and correctly and always write all the reactions required in the answer to explain it.