An herbicide is found to contain only C, H, N, and Cl. The complete combustion of a 100.0-mg sample of the herbicide in excess oxygen produces 83.16 mL of CO2 and 73.30 mL of H2O vapor expressed at STP. A separate analysis shows that the sample also contains 16.44 mg of Cl. (b) Calculate its empirical formula.

Verified step by step guidance

1. Determine the moles of CO2 and H2O produced. Use the ideal gas law or molar volume at STP (22.4 L/mol) to convert the volumes of CO2 and H2O to moles.
2. Calculate the moles of carbon from the moles of CO2 produced, assuming each mole of CO2 contains one mole of carbon.
3. Calculate the moles of hydrogen from the moles of H2O produced, assuming each mole of H2O contains two moles of hydrogen.
4. Calculate the mass of carbon and hydrogen using their respective molar masses. Subtract the masses of carbon, hydrogen, and chlorine from the total mass of the sample to find the mass of nitrogen.
5. Convert the masses of carbon, hydrogen, nitrogen, and chlorine to moles using their respective molar masses. Then, find the simplest whole number ratio of these elements to determine the empirical formula.

Key Concepts

Empirical Formula

The empirical formula represents the simplest whole-number ratio of the elements in a compound. It is determined by analyzing the mass of each element present in a sample and converting these masses into moles. The resulting mole ratios are then simplified to the smallest integers, providing a basic understanding of the compound's composition.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It allows chemists to calculate the amounts of substances consumed and produced in a reaction, which is essential for determining the empirical formula from combustion data, as it involves converting volumes of gases to moles using the ideal gas law.

Combustion Analysis

Combustion analysis is a technique used to determine the elemental composition of organic compounds. In this process, a sample is burned in excess oxygen, and the products (typically CO2 and H2O) are measured. The volumes of these gases produced can be used to calculate the amounts of carbon and hydrogen in the original sample, which are crucial for deriving the empirical formula.