Determining Empirical and Molecular Formulas of a Phosphorus-Oxygen Compound

Introduction

In chemistry, determining the empirical and molecular formulas of a compound is a fundamental step in understanding its composition and structure. For instance, consider a compound consisting of 43.64 grams of phosphorus (P) and 56.36 grams of oxygen (O). This article will guide you through the process of deriving both the empirical and molecular formulas for this compound, following Google's SEO standards for search engine optimization.

Step-by-Step Process

Step 1: Assume a 100g Sample

For simplicity and to facilitate calculation, assume a 100g sample of the compound. This assumption will help in converting the mass percentages of each element into moles.

Step 2: Calculate the Mass of Each Element

Phosphorus (P): 43.64 grams

Oxygen (O): 56.36 grams

Step 3: Convert Mass to Moles

The molar mass of phosphorus (P) is approximately 31.00 grams per mole, and for oxygen (O), it is approximately 16.00 grams per mole.

Moles of phosphorus 43.64g / 31.00g/mol ≈ 1.41 moles

Moles of oxygen 56.36g / 16.00g/mol ≈ 3.52 moles

Step 4: Find the Simplest Whole-Number Ratio

To find the simplest whole-number ratio, divide each mole value by the smallest mole value (1.41 moles).

Phosphorus: 1.41 moles / 1.41 moles 1

Oxygen: 3.52 moles / 1.41 moles ≈ 2.5

Step 5: Convert to Whole Numbers

Multiply both subscripts by 2 to convert the ratio to whole numbers:

Phosphorus: 1 × 2 2

Oxygen: 2.5 × 2 5

Step 6: Determine the Empirical Formula

The empirical formula represents the simplest whole-number ratio of atoms in a compound. For this compound, the empirical formula is PO5.

Step 7: Calculate the Empirical Formula Mass

Calculate the empirical formula mass (E.F.M) as follows:

E.F.M. (2 × 31.00g/mol) (5 × 16.00g/mol)

E.F.M. 141.98g/mol

Step 8: Determine the Molecular Formula

To determine the molecular formula, calculate the molar mass of the empirical formula and compare it to the given molar mass (283.88 g/mol).

To find the molecular formula, calculate n:

n Molecular mass / Empirical formula mass

n 283.88 g/mol / 141.98 g/mol

n ≈ 2

Thus, the molecular formula is PO10, which is the empirical formula multiplied by 2:

Molecular formula PO5? PO10

Conclusion

The process of deriving the empirical and molecular formulas for a compound like that consisting of 43.64 grams of phosphorus and 56.36 grams of oxygen involves several steps. By assuming a 100g sample and converting the masses into moles, we can then find the simplest whole-number ratio, convert it to whole numbers, and determine both the empirical and molecular formulas. This method ensures a clear and systematic approach to solving such problems.

Keywords: empirical formula, molecular formula, chemical compound