Question

Soda extract is prepared by:
A. Fusing soda and mixture and then extracting with water.
B. Dissolving $NaHC\mathop O\nolimits_3 $ and mixture in $dil.HCl$.
C. Boiling $\mathop {Na}\nolimits_2 C\mathop O\nolimits_3 $ and mixture in $dil.HCl$.
D. Boiling $\mathop {Na}\nolimits_2 C\mathop O\nolimits_3 $and mixture in distilled water.

Answer 1

Hint: It is used to identify anions in mixture which are insoluble in water and dil. acids and also it helps to prevent the cation in interfering.

Complete step by step solution:
We know that Sodium carbonate, also called soda extract is prepared during the qualitative analysis of anions present in a given mixture.
Generally, we prepare soda extract for those given compounds which are insoluble in water. It is prepared because it brings all the anions of the given sample into solution, otherwise they might be insoluble and we couldn’t carry out the experiment properly.
When the mixture under examination is partially or completely insoluble in water, then we have to prepare sodium carbonate extract. In order to prepare soda extract, we have to mix the given mixture or salt with $\mathop {Na}\nolimits_2 C\mathop O\nolimits_3 $ in 1:2 ratio and sufficient amounts of distilled water should also be added. Now, boil the whole content for 15-20 minutes and after that filter the content. The filtrate which we get after filtration is used as soda extract. For example: If $\mathop {Ca}\nolimits_3 \mathop {\left( {P\mathop O\nolimits_4 } \right)}\nolimits_2 $ is the given salt, then the reaction which will happen:
$\begin{gathered}
  \mathop {Ca}\nolimits_3 \mathop {\left( {P\mathop O\nolimits_4 } \right)}\nolimits_2 + \mathop {3Na}\nolimits_2 C\mathop O\nolimits_3 \to 3CaC\mathop O\nolimits_3 + 2\mathop {Na}\nolimits_3 P\mathop O\nolimits_4 \\
    \\
\end{gathered} $
Therefore, on above basis we can say that option D. is the correct answer.

Note: It should be noted that if ammonia is given out on boiling the mixture with sodium carbonate solution, the former must be expelled completely because it tends to complex copper, cadmium, nickel etc. into the soluble amine which goes further into the filtrate.
Also, there are some cations such as copper, arsenic and antimony which form soluble complexes with sodium carbonate and hence these cations partly go into sodium extract.