2. Is the following reaction a redox reaction? Justify your answer by showing the oxidation numbers for each element and show your work. (5 Marks)

To determine if the reaction

\[ \text{S(s)} + \text{HNO}_3(aq) \rightarrow \text{SO}_2(g) + \text{NO}(g) + \text{H}_2O(l) \]

is a redox reaction, we need to assign oxidation numbers to each element in the reaction and look for changes in these numbers.

Step 1: Assign Oxidation Numbers

1. Sulfur (S) in elemental form (S(s)):

   • Oxidation number = 0

2. HNO3 (aq):

   • Hydrogen (H) = +1
   • Nitrogen (N) = +5
   • Oxygen (O) = -2 (there are three oxygens, contributing -6)
   • The overall charge is neutral (0), which verifies: +1 + 5 + (-6) = 0.

3. SO2 (g):

   • Sulfur (S) = +4
   • Oxygen (O) = -2 (there are two oxygens, contributing -4)
   • +4 + (-4) = 0, confirming it balances.

4. NO (g):

   • Nitrogen (N) = +2
   • Oxygen (O) = -2
   • +2 + (-2) = 0, confirming it balances.

5. H2O (l):

   • Hydrogen (H) = +1 (two hydrogens, contributing +2)
   • Oxygen (O) = -2
   • +2 + (-2) = 0, confirming it balances.

Summary of Oxidation Numbers:

• Reactants:

  • S (0)
  • H (1) | N (5) | O (-2) in HNO3

• Products:

  • S (+4) in SO2
  • N (+2) in NO
  • H (1) | O (-2) in H2O

Step 2: Determine Changes in Oxidation Numbers

By comparing the oxidation numbers:

• Sulfur:

  • Changes from 0 in S(s) to +4 in SO2 (Oxidation, loss of electrons).

• Nitrogen:

  • Changes from +5 in HNO3 to +2 in NO (Reduction, gain of electrons).

Step 3: Conclusion

Since oxidation involves an increase in oxidation number (S from 0 to +4), and reduction involves a decrease in oxidation number (N from +5 to +2), we have:

• The oxidation half-reaction: \( S(s) \rightarrow SO_2(g) \)
• The reduction half-reaction: \( HNO_3(aq) \rightarrow NO(g) + \text{other products} \)

Thus, because there are elements undergoing both oxidation and reduction in this reaction, it is a redox reaction.

Final Answer:

Yes, the reaction is a redox reaction, evidenced by the oxidation of sulfur from 0 to +4 and the reduction of nitrogen from +5 to +2.

Yes, the reaction:

\[ \text{S(s)} + \text{HNO}_3(aq) \rightarrow \text{SO}_2(g) + \text{NO}(g) + \text{H}_2O(l) \]

is a redox reaction.

Oxidation Numbers:

• S(s): 0
• HNO3: H (+1), N (+5), O (-2)
• SO2: S (+4), O (-2)
• NO: N (+2), O (-2)
• H2O: H (+1), O (-2)

Changes:

• Sulfur: 0 (in S) → +4 (in SO2) (oxidation)
• Nitrogen: +5 (in HNO3) → +2 (in NO) (reduction)

Conclusion:

Since sulfur is oxidized and nitrogen is reduced, this is a redox reaction.