What is the oxidation number of the tin in Sn(OH)3-?
The Correct Answer and Explanation is:
To determine the oxidation number of tin (Sn) in the complex ion Sn(OH)₃⁻, we must use the basic rules for assigning oxidation states.
- Oxidation number of oxygen in OH⁻: The hydroxide ion (OH⁻) consists of an oxygen atom and a hydrogen atom. The oxidation number of oxygen is typically -2, while hydrogen in a compound with nonmetals is usually +1. Since the overall charge of the hydroxide ion is -1, the oxidation number of oxygen is indeed -2, and hydrogen is +1.
- Oxidation number of the whole hydroxide ion (OH⁻): Since the hydroxide ion has a charge of -1, the sum of the oxidation numbers of the atoms in the hydroxide ion must equal -1.
- Oxidation number of Sn in Sn(OH)₃⁻: The ion Sn(OH)₃⁻ contains three hydroxide ions. The oxidation numbers of the three hydroxide ions will each contribute -1 to the total charge of the complex. The total contribution from the three hydroxide ions is -3.
- Balancing the charges: The complex ion Sn(OH)₃⁻ has an overall charge of -1. To balance the charge, the oxidation number of Sn must be such that the sum of the oxidation number of Sn and the charges from the three hydroxide ions equals -1. Since the three hydroxide ions contribute -3, the oxidation number of Sn must be +2 to balance this out: x+(−3)=−1⇒x=+2x + (-3) = -1 \quad \Rightarrow \quad x = +2x+(−3)=−1⇒x=+2
Therefore, the oxidation number of Sn in Sn(OH)₃⁻ is +2.
This method uses the principle of charge balance and oxidation number rules to find the oxidation state of tin. The key is recognizing the charges of the hydroxide ions and ensuring the sum of the oxidation states equals the charge of the entire ion.
