Which species in each pair is a better oxidizing agent under standard-state conditions? (a) br2 au3 + (b) h2 ag + (c) cd2 + cr3 + (d) o2 in acidic media o2 in basic media?

(a) Au³⁺; (b) Ag⁺; (c) Cd²⁺; (d) O₂ in acidic media

Explanation:

You've had Trends in the Periodic Table. Now, here are Trends in Standard Reduction Potentials.

The strength of oxidizing agents increases from bottom to top on the left-hand side. The strength of reducing agents increases from top to bottom on the right-hand side.

Thus, for each pair of half reactions, we need to look only at which one has the more positive standard reduction potential.

(a) Br₂/Au³⁺

Au³⁺ (aq) + 3e⁻ ⟶ Au (s) 1.498 V

Br₂ (ℓ) + 2e⁻ ⟶ 2Br⁻ (aq) 1.066 V

Au³⁺ is the stronger oxidizing agent.

(b) H₂/Ag⁺

Ag⁺ (aq) + e⁻ ⟶ Au (s) 0.7996 V

H₂ (g) + 2e⁻ ⟶ 2H⁻ (aq) - 2.33 V

Ag⁺ is the stronger oxidizing agent.

(c) Cd²⁺/Cr³⁺

Cd²⁺ (aq) + e⁻ ⟶ Cd (s) - 0.4030 V

Cr³⁺ (aq) + 3e⁻ ⟶ Cr (s) - 0.744 V

Cd²⁺ is the stronger oxidizing agent.

(d) O₂, H⁺/O₂, OH⁻

O₂ (g) + 4H⁺ (aq) + 4e⁻ ⟶ 2H₂O (ℓ) 1.224 V

O₂ (g) + H₂O (ℓ) + 4e⁻ ⟶ 4OH⁻ (aq) 0.401 V

O₂ in acid is the stronger oxidizing agent.