Question

Sodium Carbonate cannot be used in place of $(NH_4)_2CO_3$ for the identification of $Ca^{2+},\, Ba^{2+}$ and $Sr^{2+}$ ions (in group V) during mixture analysis because :

• A. $Mg^{2+}$ ions will also be precipitated.
• B. Concentration of $CO_3^{2-}$ ions is very low.
• C. Sodium ions will react with add radicals.
• D. Na+ions will interfere with the detection of $Ca^{2+},\, Ba^{2+},\, Si^{2+}$ ions.

Answer 1

Answer: (A)

If $Na_2CO_3$ is used in place of $(NH_4)_2CO_3$. It will precipitate group $V$ radicals as well as magnesium radicals. The reason for this is the high ionization of $Na_2CO_3$ in water into $Na^+$ and $CO_3^{--}$. Now the higher concentration of $CO_3^{--}$ is available which exceeds the solubility product of group $V$ radicals as well as that of magnesium radicals.