Determining the Oxidation State of Phosphorus in HPO4

The chemical compound known as hydrogen phosphate has the following composition: HPO4-2 with a formal charge of -2. This involves understanding the oxidation states of all its constituent elements, particularly the phosphorus (P) element. In this article, we will explore the detailed steps to determine the oxidation state of phosphorus in HPO4-2, using both theoretical and practical approaches.

Theoretical Approach to Determining Oxidation States

First, we need to acknowledge that the anion phosphate (PO4) has a formal charge of -3. Understanding this, we know that each oxygen (O) atom contributes -2 to the overall charge of the molecule. Given this information, we can set up an equation to determine the oxidation state of phosphorus.

Step 1: Setting Up the Equation

Let's denote the oxidation state of phosphorus as x.

[ x 4(-2) -3 ]

[ x - 8 -3 ]

[ x 5 ]

This calculation shows that the oxidation state of phosphorus in HPO4-2 is 5.

Review of HPO4-2 Species

It's important to note that HPO4-2 is the correct species formed from the loss of two acidic protons (H ) from H3PO4. Let's consider the oxidation states in HPO4-2 more closely:

Step 2: Applying the Correct Species

The formula for the biphosphate anion is HPO4-2. This anion has a formal charge of -2, which must be balanced by the oxidation states of its constituent elements.

Using the same method:

[ 1(1) x 4(-2) -2 ]

[ 1 x - 8 -2 ]

[ x - 7 -2 ]

[ x 5 ]

Thus, the oxidation state of phosphorus in HPO4-2 is indeed 5.

Phosphoric Acid (H3PO4) Analysis

In phosphoric acid (H3PO4), the oxidation states of hydrogen (H), phosphorus (P), and oxygen (O) are as follows:

Oxidation state of H 1

Oxidation state of oxygen -2

Oxidation state of P x

Since the molecule is neutral, the sum of the oxidation states is 0:

[ 3(1) x 4(-2) 0 ]

[ 3 x - 8 0 ]

[ x - 5 0 ]

[ x 5 ]

This confirms that the oxidation state of phosphorus in H3PO4 is 5.

Consistency Across Different Phosphorus Containing Compounds

It is crucial to understand the consistency of the oxidation states across different phosphorus-containing compounds. For example, in compounds like HPO, where P does not form a peroxide or superoxide, the above method is still applicable:

Oxidation state of H 1

Oxidation state of O -2

Oxidation state of P x

The compound is neutral, so:

[ 1 x 4(-2) 0 ]

[ 1 x - 8 0 ]

[ x - 7 -2 ]

[ x 5 ]

Thus, the oxidation state of phosphorus remains 5 in HPO.

Conclusion

The oxidation state of phosphorus (P) in HPO4-2 and its related species, including H3PO4, is consistently determined to be 5. This consistency is crucial in understanding the behavior and properties of phosphorus in various chemical compounds. Understanding the oxidation state of phosphorus helps in predicting and analyzing its chemical reactions and interactions in complex systems.