Question

How many of the following acid radicals give colourless gas on reaction with dilute $H_2SO_4$

Answer 1

5

Answer 2

The reaction of each acid radical with dilute $H_2SO_4$ is analyzed to determine the gaseous products and their colors: \begin{itemize} \item $C_2O_4^{2-}$ (Oxalate): Reacts to form $H_2C_2O_4$, which decomposes into $CO \uparrow$ and $CO_2 \uparrow$. Both are colorless gases. \item $Br^-$ (Bromide): Reacts to form $HBr \uparrow$, which is a colorless gas. \item $NO_2^-$ (Nitrite): Reacts to form $HNO_2$, which decomposes to $NO \uparrow$. $NO$ is colorless but oxidizes in air to $NO_2$ (brown fumes). In the context of observed gases, this is considered colored. \item $CO_3^{2-}$ (Carbonate): Reacts to form $H_2CO_3$, which decomposes into $CO_2 \uparrow$. This is a colorless gas. \item $S^{2-}$ (Sulfide): Reacts to form $H_2S \uparrow$. This is a colorless gas with a characteristic rotten egg smell. \item $PO_4^{3-}$ (Phosphate): No gas is evolved. \item $SO_4^{2-}$ (Sulfate): No gas is evolved. \item $HCO_3^-$ (Bicarbonate): Reacts to form $H_2CO_3$, which decomposes into $CO_2 \uparrow$. This is a colorless gas. \end{itemize} The acid radicals that produce colorless gases are $C_2O_4^{2-}, Br^-, CO_3^{2-}, S^{2-}, HCO_3^-$. There are 5 such radicals.