Combustion Analysis and Stoichiometry

Combustion analysis is a technique to determine empirical formulas.
- It involves burning a known mass of a compound and weighing the products.
Commonly used for organic compounds containing carbon, hydrogen, and oxygen.
- Products of combustion:
- Carbon burns to form carbon dioxide (CO₂).
- Hydrogen burns to form water (H₂O).
By measuring the mass of CO₂ and H₂O produced, one can find the mass of individual elements in the original compound.
- Mass determination:
- The original mass of carbon forms CO₂.
- The original mass of hydrogen forms H₂O.
- Original oxygen mass is found through subtraction from the total mass.
After obtaining masses of elements:
- Convert grams to moles using molar masses.
- Determine the empirical formula by dividing by the smallest mole value.
- If necessary, multiply to obtain whole numbers.
Example Problem:
- 1.83 grams of CO₂ produced → convert to moles of carbon.
- Moles of CO₂ = \frac{1.83 ext{ grams CO}_2}{44.01 ext{ grams/mol}}.
- Grams to moles: 0.0416 moles of CO₂ yields 0.0416 moles of C.
0.901 grams of H₂O produced → find moles of hydrogen.
- Moles of H₂O = \frac{0.901 ext{ grams H}_2O}{18.02 ext{ grams/mol}}.
- Calculates to 0.0500 moles of H (2 moles H per molecule of H₂O).
Empirical formula derived from masses and mole ratios leads to a substance, e.g., C₅H₁₂.

Conversion of grams to moles is crucial before employing the pseudo formula.
Example of hydrocarbon combustion:
- Identify unknowns, relate masses of products to moles, and derive components.
- Calculate moles from grams and vice versa as needed.

Total sample mass weighed against moles derived from combustion products gives the final mole count for each constituent.
- Requires subtracting the mass of carbon and hydrogen to find the remaining oxygen.
- Calculate moles for oxygen, ensuring to divide quantities properly.

Stoichiometry applied to understand combustion reactions, especially CO₂ and octane relationships.
- Discusses the balance of energy conservation in chemical reactions and reliance on coefficients.
- Identifies greenhouse gases and tracking CO₂ related to fossil fuel combustion.

Highlights how numerous factors, including water vapor, influence greenhouse gas effects.
Solution-based stoichiometry and real-world applications in environmental science.

Discusses calculations to establish limiting reactants and theoretical yields in reactions.
- Includes how to analyze which reactants will run out first in a reaction context.

Introduction to aqueous solutions and molarity (mol/L) for describing concentration.
- Emphasizes the importance of accurate measurements and dilution techniques using volumetric flasks.
- Explanation of stock solutions, dilution calculations, and specific formulae (e.g., M1V1 = M2V2).

Reiterates the importance of moles in stoichiometric calculations and reactions.
Highlights the relationship between moles in a dilute solution and how dilution maintains the number of solute particles while changing the concentration.
- Example of how to use molarity for various stoichiometric calculations and real-world applications.