Percentage of Phosphorus in Phosphoric Acid: An In-Depth Analysis

Phosphoric acid, commonly represented as H3PO4, is a widely used chemical in a variety of applications, including pharmaceuticals, food processing, and household cleaning products. One fundamental question that often arises in chemical analysis is: what is the percentage of phosphorus in this molecule?

Molar Mass Calculation of Phosphoric Acid (H3PO4)

To determine the percentage of phosphorus in phosphoric acid, we first need to calculate its molar mass. The molar mass is a crucial factor in understanding the molecular weight and making precise chemical analyses.

Step-by-Step Molar Mass Calculation

Molar mass of hydrogen (H) 1 g/mol. Since there are 3 hydrogen atoms in H3PO4, the total mass of hydrogen is 3 × 1 g/mol 3 g/mol.

Molar mass of phosphorus (P) 31 g/mol. There is only one phosphorus atom in H3PO4, so its mass is 31 g/mol.

Molar mass of oxygen (O) 16 g/mol. There are 4 oxygen atoms in H3PO4, so the total mass of oxygen is 4 × 16 g/mol 64 g/mol.

Now, we add these values to find the molar mass of phosphoric acid (H3PO4):

Molar Mass of H3PO4

3 31 64 98 g/mol

Percentage Calculation of Phosphorus

To find the percentage of phosphorus in H3PO4, we use the following formula:

Percentage of P (mass of P / molar mass of H3PO4) * 100

Substituting the values, we get:

Percentage of P (31 g/mol / 98 g/mol) * 100 ≈ 31.63%

Thus, the percentage of phosphorus in phosphoric acid (H3PO4) is approximately 31.63%.

Alternative Calculations

Several alternative methods can be used to calculate the percentage of phosphorus in phosphoric acid. Here are a few examples:

Method 1

The defining quotient is the ratio of the mass of phosphorus to the molar mass of phosphoric acid: m/d, where m is the mass of phosphorus (31.0 g) and d is the molar mass of phosphoric acid (98.08 g/mol).

Multiplying by 100, we get approximately 30%.

Method 2

The total percent composition of phosphoric acid is 31.608% phosphorus, 3.0854% hydrogen, and 65.306% oxygen. This is derived from the molar masses of each component and the overall molar mass of phosphoric acid.

Method 3

We take the quotient (mass of phosphorus / molar mass of phosphoric acid) × 100. Substituting the values, we get approximately 32%.

These calculations, while slightly different, all provide similar results, confirming the accuracy of the percentage of phosphorus in phosphoric acid.