Qualitative analysis of the anionic part of a salt using it's soda extract While testing for anions using dilute $\ce{H2SO4}$, we prefer using the soda extract for tests rather than the actual salt. But we don’t use it for tests of carbonates, bicarbonates and sulphites. Why is this so?
I get that soda extract itself is a carbonate so no point to use it for carbonates but why not bicarbonates and sulphites?
Also I’m told that we use soda extract because sodium salts are mostly soluble. Then why specifically sodium? Isn’t there any other metal we can use?
If a solution of $\ce{H2SO4}$ is added to a some carbonate, bicarbonate or sulfite, it will produce some $\ce{CO2}$ or $\ce{SO2}$ effervescence with gas bubbles filling the container where this test is done, and maybe cause it to overflow. With sodium bicarbonate the equation is :
$$\ce{H2SO4  + 2 NaHCO3 -&gt; Na2SO4 + 2 H2O + 2 CO2}$$
With sodium sulfite, it is :
$$\ce{Na2SO3 + H2SO4 -&gt; Na2SO4 + H2O + SO2}$$