Question:
Small quantities of \(NO\) and \(HNO_3\) are formed as impurities when \(N_2\) is prepared from \(NH_4Cl(aq)\) and \(NaNO_2(aq)\). These impurities can be removed by passing the \(N_2\) gas through which of the following?
Small quantities of \(NO\) and \(HNO_3\) are formed as impurities when \(N_2\) is prepared from \(NH_4Cl(aq)\) and \(NaNO_2(aq)\). These impurities can be removed by passing the \(N_2\) gas through which of the following?
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During laboratory preparation of nitrogen from \(NH_4Cl\) and \(NaNO_2\), traces of nitrogen oxides may be formed. Acidified potassium dichromate is commonly used as a purification reagent because it removes these impurities while leaving \(N_2\) unaffected.
Updated On: Jul 18, 2026
- \(H_2SO_4(aq)\) containing \(SO_3\)
- \(H_2SO_4(aq)\) containing \(K_2Cr_2O_7\)
- \(H_2SO_4(aq)\) containing \(KMnO_4\)
- \(HCl(aq)\) containing \(KMnO_4\)
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The Correct Option is B
Solution and Explanation
Step 1: Write the reaction for preparation of nitrogen.
Nitrogen is prepared in the laboratory by reacting ammonium chloride with sodium nitrite. \[ NH_4Cl + NaNO_2 \rightarrow N_2 + NaCl + 2H_2O \] During the reaction, small amounts of \[ NO \] and \[ HNO_3 \] may also be formed as impurities.
Step 2: Identify the impurities to be removed.
The gaseous mixture contains: \[ N_2 + NO + HNO_3 \] We need a reagent that removes \(NO\) and acidic impurities without reacting with nitrogen gas.
Step 3: Role of acidified potassium dichromate.
Acidified potassium dichromate \[ K_2Cr_2O_7/H_2SO_4 \] is a strong oxidizing agent. It oxidizes nitric oxide (\(NO\)) to higher oxides of nitrogen, which are absorbed by the acidic medium.
The acidic medium also helps in removing traces of nitric acid and other nitrogen oxide impurities.
Nitrogen gas itself remains unaffected because it is chemically inert under these conditions.
Step 4: Examine the other options.
\[ H_2SO_4 + SO_3 \] mainly acts as a dehydrating and absorbing agent but is not suitable for complete removal of \(NO\).
\[ H_2SO_4 + KMnO_4 \] is a stronger oxidizing mixture and may lead to side reactions.
\[ HCl + KMnO_4 \] produces chlorine gas: \[ 2KMnO_4+16HCl \rightarrow 2MnCl_2+5Cl_2+2KCl+8H_2O \] which would contaminate the nitrogen sample.
Step 5: Final conclusion.
Therefore, the impurities \(NO\) and \(HNO_3\) are removed by passing the gas through \[ \boxed{H_2SO_4(aq)\ \text{containing}\ K_2Cr_2O_7} \] Hence, option (2) is correct.
Nitrogen is prepared in the laboratory by reacting ammonium chloride with sodium nitrite. \[ NH_4Cl + NaNO_2 \rightarrow N_2 + NaCl + 2H_2O \] During the reaction, small amounts of \[ NO \] and \[ HNO_3 \] may also be formed as impurities.
Step 2: Identify the impurities to be removed.
The gaseous mixture contains: \[ N_2 + NO + HNO_3 \] We need a reagent that removes \(NO\) and acidic impurities without reacting with nitrogen gas.
Step 3: Role of acidified potassium dichromate.
Acidified potassium dichromate \[ K_2Cr_2O_7/H_2SO_4 \] is a strong oxidizing agent. It oxidizes nitric oxide (\(NO\)) to higher oxides of nitrogen, which are absorbed by the acidic medium.
The acidic medium also helps in removing traces of nitric acid and other nitrogen oxide impurities.
Nitrogen gas itself remains unaffected because it is chemically inert under these conditions.
Step 4: Examine the other options.
\[ H_2SO_4 + SO_3 \] mainly acts as a dehydrating and absorbing agent but is not suitable for complete removal of \(NO\).
\[ H_2SO_4 + KMnO_4 \] is a stronger oxidizing mixture and may lead to side reactions.
\[ HCl + KMnO_4 \] produces chlorine gas: \[ 2KMnO_4+16HCl \rightarrow 2MnCl_2+5Cl_2+2KCl+8H_2O \] which would contaminate the nitrogen sample.
Step 5: Final conclusion.
Therefore, the impurities \(NO\) and \(HNO_3\) are removed by passing the gas through \[ \boxed{H_2SO_4(aq)\ \text{containing}\ K_2Cr_2O_7} \] Hence, option (2) is correct.
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