CFCs, Mass Percent Calculations, and Combustion Analysis

Overview of CFCs and Environmental Chemistry

• CFC: Stands for chlorofluorocarbon.

  • Definition: A type of refrigerant known for depleting the ozone layer.

  • Common Uses: Utilized in refrigeration for food preservation and energy efficiency.

Calculation of Mass Percentages

Example 1: Mass percent of Chlorine in CFC (Freon-12)

• Chemical Formula: $C<em>2Cl</em>4F_2$ (Freon-12)

  • Distribution of Elements:

  • Chlorine (Cl): 4 atoms

  • Mass of Chlorine: Each chlorine atom weighs 35.45 g.

    • $4 imes 35.45 ext{g} = 141.8 ext{g}$

  • Carbon (C): 2 atoms

    • $2 imes 12.01 ext{g} = 24.02 ext{g}$

  • Fluorine (F): 2 atoms

    • $2 imes 18.998 ext{g} = 37.996 ext{g}$

  • Total: $ext{Mass of Freon-12} = 141.8 + 24.02 + 37.996 = 203.816 ext{g}$

• Mass Percent of Chlorine:

  • $ext{MassPercent}_{Cl} = rac{ ext{mass of Cl}}{ ext{total mass}} imes 100$

  • $ext{MassPercent}_{Cl} = rac{141.8}{203.816} imes 100 <br>ightarrow 69.57 ext{(correct rounding)}$

Example 2: Mass percent of Oxygen in Acetic Acid

• Chemical Formula: $C<em>2H</em>4O_2$ (Acetic Acid)

• Distribution of Elements:

  • Carbon (C): 2 atoms

    • $2 imes 12.011 ext{g} = 24.022 ext{g}$

  • Hydrogen (H): 4 atoms

    • $4 imes 1.008 ext{g} = 4.032 ext{g}$

  • Oxygen (O): 2 atoms

    • $2 imes 15.999 ext{g} = 31.998 ext{g}$

• Total Mass: $ext{TotalMass}<em>{C</em>2H<em>4O</em>2} = 24.022 + 4.032 + 31.998 = 60.052 ext{g}$

• Mass Percent of Oxygen:

  • $ext{MassPercent}_{O} = rac{ ext{mass of O}}{ ext{total mass}} imes 100$

  • $ext{MassPercent}_{O} = rac{31.998}{60.052} imes 100 <br>ightarrow 53.33 ext{(with adjustments)}$

Practice with Experimental Values

Example 3: Analyzing Pepto-Bismol

• Pepto-Bismol Composition: $C<em>7H</em>5BiO_4$ (Bismuth Subsalicylate)

• Sample Mass: 1.5 g of Pepto-Bismol

• Extracted Mass of Bismuth: 346 mg (or 0.346 g)

• Mass Percent Calculation:

  • Find the molecular weight of Bismuth Subsalicylate, identify the mass contribution of bismuth, hydrogen, carbon, and oxygen.

  • Calculate using total mass and individual contributions.

Steps to determine mass of Bismuth Subsalicylate in sample:

• Calculate empirical mass with the formula.

• Divide the measured bismuth mass by the calculated mass percent (derived from empirical chemical formulas).

Understanding Molecular Formulas and Empirical Formulas

• Empirical Formula: Simplest integer ratio of atoms in a compound.

• Molecular Formula: Actual number of atoms of each element in a molecule.

• To calculate the molecular formula from the empirical formula, you need:

  • Empirical mass and Molecular mass.

• N Calculation:

  • $N = rac{ ext{Molecular Mass}}{ ext{Empirical Mass}}$

Combustion Analysis for Compounds

Introduction to Combustion Analysis

• Objective: To deduce empirical formulas by analyzing products of combustion (usually $CO<em>2$ and $H</em>2O$)

• Procedure: Expose a compound to oxygen and measure the resulting amounts of $CO<em>2$ and $H</em>2O$ produced.

Example Problem of Combustion

Consider a compound that produces 183 g of $CO<em>2$ and 0.901 g of $H</em>2O$:

• Calculation Steps:

  1. Convert mass of $CO_2$ to moles to find the amount of Carbon:

  2. Convert mass of $H_2O$ to moles to find the amount of Hydrogen:

  3. Subtract the total H and C from the initial mass to find the total O.

  4. Use ratios to get empirical formula using smallest number of moles.

Final Thoughts and General Practice Tips

• Ensure understanding of mass percent calculations and conversions between grams/moles.

• Review empirical versus molecular formulas rigorously, relying on practicing various examples.

• Remember rounding rules: Keep precision until calculations are complete, round according to final needed precision.

• Understand combustion's role in organic chemistry and analysis of unknown compounds.