Determining the Molecular Formula from Given Empirical and Molar Mass Data
Introduction:
Understanding how to determine the molecular formula from an empirical formula and molar mass is a fundamental concept in analytical chemistry. This article will guide you through the process, using specific examples to illustrate the steps involved.
Step-by-Step Process to Find the Molecular Formula
1. Calculate the Molar Mass of the Empirical Formula:
Let's begin with the empirical formula C?H?O. We need to calculate the molar mass of this empirical formula.
Calculation of Empirical Formula Molar Mass:
[M(C) 12.01 g/mol] × 3 36.03 g/mol (for Carbon)
[M(H) 1.008 g/mol] × 6 6.048 g/mol (for Hydrogen)
[M(O) 16.00 g/mol] × 1 16.00 g/mol (for Oxygen)
Total Molar Mass of the Empirical Formula:
36.03 6.048 16.00 58.078 g/mol
2. Determine the Ratio:
Ratio Calculation:
Ratio Molar Mass of Molecular Formula / Molar Mass of Empirical Formula
116 g/mol / 58.078 g/mol ≈ 2
3. Multiply the Subscripts in the Empirical Formula:
Multiplication Steps:
Carbon (C): 3 × 2 6
Hydrogen (H): 6 × 2 12
Oxygen (O): 1 × 2 2
Molecular Formula: C?H??O?
Further Examples for Practice:
Example 1: If the empirical formula is C?H?O and the molar mass of the molecular formula is 168 g/mol, we follow similar steps.
1. Calculate the Molar Mass of the Empirical Formula:
[M(C) 12.01 g/mol] × 3 36.03 g/mol (for Carbon)
[M(H) 1.008 g/mol] × 4 4.032 g/mol (for Hydrogen)
[M(O) 16.00 g/mol] × 1 16.00 g/mol (for Oxygen)
Total Molar Mass of the Empirical Formula:
36.03 4.032 16.00 56.062 g/mol
2. Determine the Ratio:
Ratio Molar Mass of Molecular Formula / Molar Mass of Empirical Formula
168 g/mol / 56.062 g/mol ≈ 3
3. Multiply the Subscripts in the Empirical Formula:
Carbon (C): 3 × 3 9
Hydrogen (H): 4 × 3 12
Oxygen (O): 1 × 3 3
Molecular Formula: C?H??O?
Additional Considerations:
In many cases, it's necessary to verify the molecular formula with experimental data. The steps followed here should be a good starting point. For the compound with empirical formula C?H?O and molecular formula mass 116 g/mol, we followed these steps and arrived at the molecular formula C?H??O?.
Conclusion:
Understanding the process of determining the molecular formula from the empirical formula and molar mass is crucial for chemical analysis. By following these steps, practitioners can accurately identify and characterize compounds in a variety of scientific and industrial applications.
Keywords:
empirical formula, molar mass, molecular formula