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Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Solution: 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 at STP. A separ

Problem

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 at STP. A separate analysis shows that the sample also contains 16.44 mg of Cl.

Calculate its empirical formula.

Solution

We are asked to determine the empirical formula of the herbicide containing 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 H2vapor at STP. A separate analysis shows that the sample also contains 16.44 mg of Cl.

Recall:

Standard temperature and pressure (STP) is defined as 0°Celsius, and 1.00 atmospheres, respectively. Avogadro determined that the volume of any gas measured at STP is 22.4 L. This value is used in many gas conversions from liters to moles, or vice-versa, as long as the STP conditions are met

The empirical formula is a chemical formula showing the simplest (or lowest) whole number ratio of elements in a compound.

To solve this problem, we shall follow these steps:

Step 1: Convert the given quantities from mg to g and from mL to L.

Step 2: Convert volumes of products to moles of products (mol/22.4 L).

Step 3: Perform a mole-to-mole comparison (1 mol C:1 mol CO2; 2 mol H: 1 mol H2O).

Step 4: Determine the mass of C and H using their respective molar mass.

Step 5: Determine the total mass of C, H, and Cl. From here, determine the mass of N.

Step 6: Determine the moles of N and Cl using their respective molar mass. 

Step 7: Determine the empirical formula by dividing the moles with the smallest number of moles.

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