Question

What is sodium carbonate extract? What is its utility in qualitative analysis?

Answer 1

Hint: Sodium carbonate extract is used when salt is insoluble in water for the confirmation of anion. Whereas water extract of inorganic salt is used when salt is soluble in water. Water extract is prepared by dissolving unknown inorganic compounds in water.

Complete step by step solution
For the confirmatory analysis of acidic radicals we use the soda extract or sodium carbonate extract. It is prepared when the given inorganic compound is insoluble in water.
Preparation of sodium carbonate extract: to prepare the sodium carbonate extract take $ 1:3 $ ratio of unknown salt and sodium carbonate in $ 15\text{ ml} $ of water i.e. one part of salt to the 3 part of sodium carbonate. Boil the mixture for 15 minutes and then filter off. The filtrate in the beaker is known as sodium carbonate extract.
When we boil the mixture the following reaction takes place.
Example: $ \text{Ca}{{\text{C}}_{2}}{{\text{O}}_{4}}+\text{N}{{\text{a}}_{2}}\text{C}{{\text{O}}_{3}}\to \text{CaC}{{\text{O}}_{3}}+\text{N}{{\text{a}}_{2}}\text{ }{{\text{C}}_{2}}{{\text{O}}_{4}} $
 $ \text{CaC}{{\text{O}}_{3}} $ is insoluble in water left as reside whereas $ \text{N}{{\text{a}}_{2}}{{\text{C}}_{2}}{{\text{O}}_{4}} $ is soluble in water it is taken as filtrate which is soda extract.
Before the detection of the oxide radicals firstly acidified the soda extract by sulphate acid because sodium carbonate is basic in nature.
Utility of sodium carbonate extract in Qualification analysis
It is used for the detection of anion in the mixture when the numbers of salts are insoluble in water and dilute acids.
It removes the basic radicals from the salt in residence which interfere in the detection of acidic radicals because the same basic radicals impart the color to the solution.
The residence is also used as it contains basic radicals. It is particularly used to detect basic radicals of group 1 to group V for the purpose of dissolving the residue in direct or cone HCl .

Note
As sodium carbonate extract is used to detect the acidic radicals in noryanie chemistry. Question arises what are acidic and basic radicals.
Acidic radicals: The negatively charged radicals or ions is called acidic radicals as $ \text{c}{{\text{l}}^{-}},\text{ }{{\text{F}}^{-}},\text{ S}{{\text{o}}_{4}}^{+} $ etc.
Basic radicals: The positively charged radicals are called basic radicals.
Example $ \text{B}{{\text{a}}^{++}},{{\text{K}}^{+}},\text{N}{{\text{a}}^{+}},\text{M}{{\text{g}}^{2+}} $ etc.
Salts are formed by both i.e. it is a combination of acidic and basic radical.
Examples: $ {{\text{k}}^{+}}\text{c}{{\text{l}}^{-}},\text{ N}{{\text{a}}^{+}}\text{c}{{\text{l}}^{-}},\text{ Ba ci,} $ etc.