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)

Question

S(s) + HNO3 (aq ) → SO2 (g) + NO (g) + H2O (l)

Answer 1

To determine if the reaction $S(s)+HN{O}_3(aq)\to S{O}_2(g)+NO(g)+H_{2}O(l)$ is a redox reaction, we can analyze the oxidation states (oxidation numbers) of the elements involved before and after the reaction.

Step 1: Assign oxidation states

1. Reactants:

   • Sulfur ($S$): In its elemental form, sulfur has an oxidation state of 0.
   • Hydrogen ($H$) in $HN{O}_3$: The oxidation state of hydrogen is +1.
   • Nitrogen ($N$) in $HN{O}_3$: The oxidation state of nitrogen can be calculated as follows:
     • The total charge of $HN{O}_3$ is 0.
     • $H:+1$
     • $O:-2\times 3=-6$
     • Let the oxidation state of $N$ be $x$.
     • Therefore: $$+1+x-6=0⟹x=+5$$
   • Oxygen ($O$) in $HN{O}_3$: The oxidation state of oxygen is -2.

2. Products:

   • Sulfur ($S$) in $S{O}_2$:
     • The total charge of $S{O}_2$ is 0.
     • Let the oxidation state of $S$ be $y$.
     • So we have: $$y-2\times 2=0⟹y=+4$$
   • Nitrogen ($N$) in $NO$:
     • The total charge of $NO$ is 0.
     • Let the oxidation state of $N$ be $z$.
     • Therefore: $$z-2=0⟹z=+2$$
   • Hydrogen ($H$) in $H_{2}O$: The oxidation state of hydrogen is +1.
   • Oxygen ($O$) in $H_{2}O$: The oxidation state of oxygen is -2.

Step 2: Summary of oxidation states

• Reactants:

  • $S:0$
  • $H:+1$ (from $HN{O}_3$)
  • $N:+5$ (from $HN{O}_3$)
  • $O:-2$ (from $HN{O}_3$)

• Products:

  • $S:+4$ (from $S{O}_2$)
  • $N:+2$ (from $NO$)
  • $H:+1$ (from $H_{2}O$)
  • $O:-2$ (from $H_{2}O$)

Step 3: Determine changes in oxidation states

• Sulfur ($S$):

  • Changes from 0 (reactant) to +4 (product) = oxidation (loss of electrons).

• Nitrogen ($N$):

  • Changes from +5 (reactant) to +2 (product) = reduction (gain of electrons).

Conclusion:

Since there is a change in oxidation states for both sulfur and nitrogen, this indicates that oxidation and reduction processes are occurring. Therefore, we identify this reaction as a redox reaction.

Final Verdict: Yes, this reaction is a redox reaction due to the changes in oxidation states of sulfur (oxidation) and nitrogen (reduction).