Question

What is the oxidation state of Phosphorus in \( H_3PO_4 \)?

• A. \(+3\)
• B. \(+5\)
• C. \(+1\)
• D. \(+7\)

Hint:

For neutral molecules, the sum of oxidation numbers is zero. Use common values such as \(H = +1\) and \(O = -2\) to easily determine the unknown oxidation state.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
We need to determine the oxidation number (or state) of the phosphorus (P) atom in the phosphoric acid molecule (\( H_3PO_4 \)).
Step 2: Key Formula or Approach:
We use the following rules for assigning oxidation states:
1. The oxidation state of H is usually +1 when bonded to nonmetals.
2. The oxidation state of O is usually -2 in most compounds.
3. The sum of the oxidation states of all atoms in a neutral molecule is zero.
Step 3: Detailed Explanation:
Let the oxidation state of phosphorus be \( x \).
The molecule is \( H_3PO_4 \).
- There are 3 hydrogen atoms, each with an oxidation state of +1. Total contribution = \( 3 \times (+1) = +3 \).
- There is 1 phosphorus atom with an unknown oxidation state \( x \). Total contribution = \( x \).
- There are 4 oxygen atoms, each with an oxidation state of -2. Total contribution = \( 4 \times (-2) = -8 \).
The sum of these must be zero because \( H_3PO_4 \) is a neutral molecule. \[ (+3) + (x) + (-8) = 0 \] \[ x - 5 = 0 \] \[ x = +5 \] Step 4: Final Answer:
The oxidation state of Phosphorus in \( H_3PO_4 \) is +5.