Problem 17 - Chemistry An Atoms First Approach

Question

Specify which of the following equations represent oxidationreduction reactions, and indicate the oxidizing agent, the reducing agent, the species being oxidized, and the species being reduced. a. \(\mathrm{CH}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) \rightarrow \mathrm{CO}(g)+3 \mathrm{H}_{2}(g)\) b. \(2 \mathrm{AgNO}_{3}(a q)+\mathrm{Cu}(s) \rightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(a q)+2 \mathrm{Ag}(s)\) c. \(\mathrm{Zn}(s)+2 \mathrm{HCl}(a q) \rightarrow \mathrm{ZnCl}_{2}(a q)+\mathrm{H}_{2}(g)\) d. \(2 \mathrm{H}^{+}(a q)+2 \mathrm{CrO}_{4}^{2-}(a q) \rightarrow \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\)

Step-by-Step Solution

Answer

Reactions a, b, and c are redox reactions with the following agents and species: a. Oxidizing agent: \(H_2O(g)\), Reducing agent: \(CH_4(g)\), Species oxidized: C in \(CH_4(g)\), Species reduced: O in \(H_2O(g)\) b. Oxidizing agent: \(AgNO_3(aq)\), Reducing agent: \(Cu(s)\), Species oxidized: \(Cu(s)\), Species reduced: \(Ag^+(aq)\) c. Oxidizing agent: \(HCl(aq)\), Reducing agent: \(Zn(s)\), Species oxidized: \(Zn(s)\), Species reduced: \(H^+(aq)\) Reaction d is not a redox reaction as there is no change in the oxidation state of any elements involved.

Step 1: Determine the oxidation states of the elements involved

First, we should assign oxidation states to each element in the reactants and products of the given reactions: a. \(\mathrm{CH}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) \rightarrow \mathrm{CO}(g)+3 \mathrm{H}_{2}(g)\) C: -4 to +2, H: +1 to 0, O: -2 to -2 b. \(2 \mathrm{AgNO}_{3}(a q)+\mathrm{Cu}(s) \rightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(a q)+2 \mathrm{Ag}(s)\) Ag: +1 to 0, N: +5 to +5, O: -2 to -2, Cu: 0 to +2 c. \(\mathrm{Zn}(s)+2 \mathrm{HCl}(a q) \rightarrow \mathrm{ZnCl}_{2}(a q)+\mathrm{H}_{2}(g)\) Zn: 0 to +2, Cl: -1 to -1, H: +1 to 0 d. \(2 \mathrm{H}^{+}(a q)+2 \mathrm{CrO}_{4}^{2-}(a q) \rightarrow \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\) H: +1 to +1, Cr: +6 to +6, O: -2 to -2

Step 2: Identify redox reactions and their components

Now, let's identify which of the given reactions are redox reactions and determine their oxidizing agent, reducing agent, species being oxidized, and species being reduced: a. \(\mathrm{CH}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) \rightarrow \mathrm{CO}(g)+3 \mathrm{H}_{2}(g)\) Redox reaction (yes) Oxidizing agent: \(\mathrm{H}_{2}\mathrm{O}(g)\) Reducing agent: \(\mathrm{CH}_{4}(g)\) Species being oxidized: C in \(\mathrm{CH}_{4}(g)\) Species being reduced: O in \(\mathrm{H}_{2}\mathrm{O}(g)\) b. \(2 \mathrm{AgNO}_{3}(a q)+\mathrm{Cu}(s) \rightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(a q)+2 \mathrm{Ag}(s)\) Redox reaction (yes) Oxidizing agent: \(\mathrm{AgNO}_{3}(a q)\) Reducing agent: \(\mathrm{Cu}(s)\) Species being oxidized: \(\mathrm{Cu}(s)\) Species being reduced: \(\mathrm{Ag}^{+}(a q)\) c. \(\mathrm{Zn}(s)+2 \mathrm{HCl}(a q) \rightarrow \mathrm{ZnCl}_{2}(a q)+\mathrm{H}_{2}(g)\) Redox reaction (yes) Oxidizing agent: \(\mathrm{HCl}(a q)\) Reducing agent: \(\mathrm{Zn}(s)\) Species being oxidized: \(\mathrm{Zn}(s)\) Species being reduced: \(\mathrm{H}^{+}(a q)\) d. \(2 \mathrm{H}^{+}(a q)+2 \mathrm{CrO}_{4}^{2-}(a q) \rightarrow \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\) Redox reaction (no) There is no change in the oxidation state of any elements involved. In summary, reactions a, b, and c are redox reactions, and for each reaction, we have identified the oxidizing agent, reducing agent, species being oxidized, and species being reduced. Reaction d is not a redox reaction.