Question

Which of the following pairs will give chlorine gas most quickly, upon reaction?

• A. $\mathrm{HCl}$and ${\mathrm{KMnO}}_4$
• B. $\mathrm{NaCl}$and ${\mathrm{H}}_3{\mathrm{PO}}_4$
• C. $\mathrm{NaCl}$and ${\mathrm{MnO}}_2$
• D. ${\mathrm{CaCl}}_2$and ${\mathrm{Br}}_2$

Answer 1

The correct option is A

$\mathrm{HCl}$and ${\mathrm{KMnO}}_4$

The explanation for the correct answer

(A) $\mathbf{HCl}\mathbf{}$and ${\mathbf{KMnO}}_{\mathbf{4}}$

• ${\mathrm{KMnO}}_4$is a good oxidizing agent
• It oxidizes $\mathrm{HCl}$and readily produces ${\mathrm{Cl}}_2$gas.
• The reaction can be written as
• $$\begin{gathered} 2{\mathrm{KMnO}}_4\left(\mathrm{s}\right)+16\mathrm{HCl}\left(\mathrm{aq}\right)\to 2\mathrm{KCl}\left(\mathrm{aq}\right)+2{\mathrm{MnCl}}_2\left(\mathrm{aq}\right)+8{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+5{\mathrm{Cl}}_2\left(\mathrm{g}\right) \\ (\mathrm{Potassium}(\mathrm{Hydrochloric}(\mathrm{Potassium}(\mathrm{Manganese}\left(\mathrm{II}\right)\left(\mathrm{Water}\right)\left(\mathrm{Chlorine}\right) \\ \mathrm{permanganate})\mathrm{acid})\mathrm{Chloride})\mathrm{Chloride}) \end{gathered}$$

Hence, Option (A) $\mathbf{HCl}\mathbf{}$and ${\mathbf{KMnO}}_{\mathbf{4}}$ is correct

The explanation for the incorrect answer

(B) $\mathbf{NaCl}\mathbf{}$and ${\mathbf{H}}_{\mathbf{3}}{\mathbf{PO}}_{\mathbf{4}}$

• The reaction between $\mathrm{NaCl}$and ${\mathrm{H}}_3{\mathrm{PO}}_4$can be written as
• $$\begin{gathered} 3\mathrm{NaCl}\left(\mathrm{aq}\right)+{\mathrm{H}}_3{\mathrm{PO}}_4\left(\mathrm{aq}\right)\to 3\mathrm{HCl}\left(\mathrm{aq}\right)+{\mathrm{Na}}_3{\mathrm{PO}}_4\left(\mathrm{aq}\right) \\ (\mathrm{Sodium}(\mathrm{Phosphoric}(\mathrm{Hydrochloric}(\mathrm{Sodium} \\ \mathrm{Chloride})\mathrm{acid})\mathrm{acid})\mathrm{Phosphate}) \end{gathered}$$
• This reaction does not produce ${\mathrm{Cl}}_2$gas.

(C) $\mathbf{NaCl}\mathbf{}$and ${\mathbf{MnO}}_{\mathbf{2}}$

• The reaction between $\mathrm{NaCl}$and ${\mathrm{MnO}}_2$can be written as
• $$\begin{gathered} 2\mathrm{NaCl}\left(\mathrm{aq}\right)+{\mathrm{MnO}}_2\left(\mathrm{aq}\right)\to {\mathrm{Na}}_2\mathrm{O}\left(\mathrm{s}\right)+\mathrm{MnO}\left(\mathrm{s}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right) \\ (\mathrm{Sodium}(\mathrm{Manganese}\left(\mathrm{IV}\right)(\mathrm{Disodium}(\mathrm{Manganese}\left(\mathrm{II}\right)\left(\mathrm{Chlorine}\right) \\ \mathrm{Chloride})\mathrm{Oxide})\mathrm{Oxide})\mathrm{Oxide}) \end{gathered}$$
• Here Chlorine gas is evolved but in less amount.

(D) ${\mathbf{CaCl}}_{\mathbf{2}\mathbf{}}$and ${\mathbf{Br}}_{\mathbf{2}}$

• The reaction between ${\mathrm{CaCl}}_2$and ${\mathrm{Br}}_2$can be written as
• $$\begin{gathered} {\mathrm{CaCl}}_2\left(\mathrm{aq}\right)+{\mathrm{Br}}_2\left(\mathrm{g}\right)\to {\mathrm{CaBr}}_2\left(\mathrm{aq}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right) \\ (\mathrm{Calcium}(\mathrm{Bromine})(\mathrm{Calcium}\left(\mathrm{Chlorine}\right) \\ \mathrm{chloride})\mathrm{Bromide}) \end{gathered}$$
• Here Chlorine gas is evolved but in less amount.

Therefore, Option (A) $\mathbf{HCl}\mathbf{}$and ${\mathbf{KMnO}}_{\mathbf{4}}\mathbf{}$is correct.