Final answer:
The oxidation number of arsenic in the arsenate ion AsO₄³⁻(aq) is +5, determined by knowing that oxygen has an oxidation number of -2 and the overall charge of the ion is -3.
Step-by-step explanation:
Determining the Oxidation Number of Arsenic in AsO₄³⁻(aq)
To determine the oxidation number of arsenic in the arsenate ion AsO₄³⁻(aq), we need to use the known oxidation numbers of the other elements and the overall charge of the ion. Oxygen generally has an oxidation number of -2. Since there are four oxygen atoms, their total oxidation number is -2 x 4 = -8. The overall charge of the ion is -3, so the sum of the oxidation numbers of arsenic and oxygen must equal -3:
As + (-8) = -3
This equation simplifies to As = -3 + 8, which gives As = +5. Therefore, the oxidation number of arsenic in AsO₄³⁻ is +5.