What is the oxidation number of Pin Ba(H2PO4)2?
A +1
B. +2
C. +3
D. +4
E. +5
F. +6
The Correct Answer and Explanation is :
The correct answer is A. +1.
To understand why, let’s break down the oxidation numbers in Ba(H₂PO₄)₂, which is barium dihydrogen phosphate.
- Identify the elements in the compound:
- Ba (Barium): This is an alkaline earth metal.
- H₂PO₄ (Dihydrogen phosphate ion): This is the complex ion composed of hydrogen, phosphorus, oxygen, and hydrogen again.
- Oxidation number rules:
- The oxidation number of oxygen is typically -2.
- The oxidation number of hydrogen is +1 when it is bonded to nonmetals (like in H₂PO₄⁻).
- The sum of the oxidation numbers of all atoms in a neutral molecule must equal zero.
- Analyze the dihydrogen phosphate ion (H₂PO₄⁻):
- The total charge on the H₂PO₄ ion is -1.
- Hydrogen atoms each contribute +1, so the two hydrogens contribute +2.
- Oxygen atoms each contribute -2, and since there are four oxygens, they contribute -8.
- To balance the charges, the phosphorus (P) atom must contribute +5 to make the total charge of the ion equal to -1:
[
+2 \, (\text{from H}) + x \, (\text{from P}) + (-8) \, (\text{from O}) = -1
]
[
+2 + x – 8 = -1 \quad \Rightarrow \quad x = +5
]
- Now consider Ba (Barium):
- Barium is in Group 2 of the periodic table, so it has an oxidation number of +2 in ionic compounds, such as Ba²⁺.
- However, Ba is paired with two dihydrogen phosphate ions (H₂PO₄⁻), each with a charge of -1. To balance the charges, Ba must have an oxidation number of +2, which compensates for the two -1 charges from the H₂PO₄⁻ ions.
Therefore, the oxidation number of Ba in Ba(H₂PO₄)₂ is +2.
This confirms that the correct answer is B. +2, not A.