Chemistry - Salt Analysis Question with Solution | TestHub

Explain the question: Count colourless gases in dil. acid group. Concept: Action of dilute acids on anions. Solution:

Anions in the "dilute acid group" react with dilute HCl or dilute ${\mathrm{H}}_2{\mathrm{SO}}_4$ to liberate gases. We evaluate each ion from the list to see if the evolved gas is colourless:${\mathrm{CO}}_3^{2-}$ (Carbonate): Evolves ${\mathrm{CO}}_2$, which is colourless and odourless (turns lime water milky). ${\mathrm{HCO}}_3^{-}$(Bicarbonate): Also evolves ${\mathrm{CO}}_2$, which is colourless. ${\mathrm{SO}}_3^{2-}$ (Sulfite): Evolves ${\mathrm{SO}}_2$, which is a colourless gas with a pungent smell of burning sulfur. ${\mathrm{HSO}}_3^{-}$(Bisulfite): Also evolves ${\mathrm{SO}}_2$, which is colourless. ${\mathrm{NO}}_2^{-}$(Nitrite): Evolves ${\mathrm{NO}}_2$, which is a reddish-brown (colored) gas. ${\mathrm{S}}_2{\mathrm{O}}_3^{2-}$ (Thiosulfate): Evolves ${\mathrm{SO}}_2$ (along with yellow sulfur precipitate), which is colourless. ${\mathrm{S}}^{2-}$ (Sulfide): Evolves ${\mathrm{H}}_2\mathrm{S}$, which is a colourless gas with a rotten egg smell.

${\mathrm{CH}}_3{\mathrm{COO}}^{-}$(Acetate): Evolves ${\mathrm{CH}}_3\mathrm{COOH}$ (acetic acid) vapors, which are colourless and have a vinegar-like smell.

From the list, only ${\mathrm{NO}}_2^{-}$produces a colored gas $\left({\mathrm{NO}}_2\right)$. All other seven anions produce colourless products. The total number of anions is 7 . Final Answer: 7.