Determining the Empirical Formula of a Compound with 40 Carbon, 6.7 Hydrogen, and 53.3 Oxygen by Mass

Evaluating the chemical composition of a compound from its mass percentages is an essential skill in analytical chemistry. This article will guide you through the process of determining the empirical formula for a compound that contains 40% carbon (C), 6.7% hydrogen (H), and 53.3% oxygen (O) by mass. Understanding how to calculate the empirical formula is crucial for chemists and anyone involved in research or development that requires precise chemical analysis.

Converting Mass Percentages to Grams

First, you need to convert the mass percentages to grams in a 100 g sample. This conversion is a straightforward process where each percentage is interpreted as the mass in grams.

Convert mass percentages to grams: 40% carbon 40.0 g 6.7% hydrogen 6.7 g 53.3% oxygen 53.3 g

Calculating Mole Ratios

Next, use the formula for moles: n m/M, where n is the number of moles, m is the mass in grams, and M is the molar mass. You can find the molar masses of the elements on the periodic table.

Molar masses: Carbon (C): 12.011 g/mol Hydrogen (H): 1.008 g/mol Oxygen (O): 15.999 g/mol Calculate the moles of each element: Carbon (C): nC 40.0 g / 12.011 g/mol 3.33 mol Hydrogen (H): nH 6.7 g / 1.008 g/mol 6.66 mol Oxygen (O): nO 53.3 g / 15.999 g/mol 3.33 mol Calculate the mole ratio: C: 3.33 mol / 3.33 mol 1 H: 6.66 mol / 3.33 mol 2 O: 3.33 mol / 3.33 mol 1 Empirical formula: The ratios are whole numbers, indicating that the empirical formula is CHO.

Calculating the Empirical Formula Mass

The empirical formula mass can be calculated using the formula: Empirical formula mass Σ (molar mass of each element × subscript).

Calculate the empirical formula mass: Empirical formula mass (12.011 g/mol for C) (2 × 1.008 g/mol for H) (15.999 g/mol for O) 30.026 g/mol

Calculating the Molecular Formula

To determine the molecular formula, you need to know the molar mass of the compound. If it is provided or needs to be calculated, divide the molar mass by the empirical formula mass.

Molecular formula: Molar mass 60.026 g/mol (hypothetical value) Molecular formula Molecular mass / Empirical formula mass 60.026 g/mol / 30.026 g/mol 2 Empirical formula (CHO) multiplied by 2: CHO CHO2

Conclusion

After following these detailed steps, you have determined that the empirical formula for the compound is CHO, and the molecular formula, assuming the molar mass provided, is CHO2. This method can be applied to a wide range of compounds, making it a valuable tool in analytical chemistry.

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