Problem 73 - Chemistry The Molecular Nature of Matter

Question

Ereon is a trade name for a group of gaseous compounds once used as propellants in aerosol cans. Which has a higher percentage of chlorine: Freon-12 \(\left(\mathrm{CCl}_{2} \mathrm{~F}_{2}\right)\) or Freon-141b \(\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}_{2} \mathrm{~F}\right) ?\)

Step-by-Step Solution

Answer

Freon-12 has a chlorine percentage of about 58.68% and Freon-141b has about 60.68%. Therefore, Freon-141b has a higher percentage of chlorine.

Step 1: Calculate the Molar Mass of Freon-12

Calculate the molar mass of Freon-12 ((CCl2F2)) by summing the atomic masses of each atom in the molecule: 2 atoms of chlorine (Cl), 2 atoms of fluorine (F), and 1 atom of carbon (C). The atomic masses (rounded to nearest whole number) are roughly 35.5 for Cl, 19 for F, and 12 for C. The calculation is as follows: Molar Mass of Freon-12 = (2 * 35.5) + (2 * 19) + (12) = 121 grams per mole.

Step 2: Calculate the Percent Composition of Chlorine in Freon-12

Compute the percentage of chlorine in Freon-12 by dividing the total mass of chlorine in the compound by the molar mass of Freon-12 and then multiplying by 100: Percent Chlorine in Freon-12 = (2 * 35.5 / 121) * 100.

Step 3: Calculate the Molar Mass of Freon-141b

Find the molar mass of Freon-141b ((C2H3Cl2F)) by summing the atomic masses for each atom in the molecule: 3 atoms of hydrogen (H), 2 atoms of chlorine (Cl), 1 atom of fluorine (F), and 2 atoms of carbon (C). The atomic masses are roughly 1 for H, 35.5 for Cl, 19 for F, and 12 for C. The calculation is: Molar Mass of Freon-141b = (2 * 35.5) + (3 * 1) + (19) + (2 * 12) = 117 grams per mole.

Step 4: Calculate the Percent Composition of Chlorine in Freon-141b

Determine the percentage of chlorine in Freon-141b by dividing the total mass of chlorine in the compound by the molar mass of Freon-141b and then multiplying by 100: Percent Chlorine in Freon-141b = (2 * 35.5 / 117) * 100.

Step 5: Compare the Chlorine Percentages

Compare the calculated percentages of chlorine in both compounds. The compound with the higher percentage represents the one with a higher content of chlorine.

Key Concepts

Molar Mass

Understanding molar mass is crucial when diving into the world of chemistry. It represents the mass of one mole of a substance, usually in grams per mole. Think of it as a chemical's 'weight sticker,' telling you how heavy a single mole is.

For instance, in our exercise example, calculating the molar mass of Freon-12 involves adding the atomic weights of each atom within the molecule. Each element on the periodic table has a known atomic mass, and since a molecule is simply a combination of these atoms, its molar mass is the total mass of all individual atoms in one mole of the molecules.

This calculation might look something like stacking blocks with each block's weight written on it. If you know the weight of each block, you can easily determine the entire stack's weight by adding them together.

Chemical Composition

Chemical composition lets you break down what's in a compound, like reading an ingredient label on a food package. It tells us the types and quantities of atoms in a substance. In the case of Freon, we're interested in the amount of chlorine it contains compared to other elements.

By determining the chemical composition of a substance, we gain insight into its properties and reactions it may undergo. In our exercise, the percentage of chlorine within different Freon compounds provides a clear example of how varying chemical compositions can influence a product's characteristics, such as its effectiveness as a refrigerant or its impact on the environment as a propellant.

Stoichiometry

Stoichiometry is the quantitative relationship between the elements in a chemical reaction. It's like a recipe – if you know how much of each ingredient you need, you can predict the amount of the final dish.

In our earlier example, we calculated the molar mass and then used stoichiometry to find the percent composition of chlorine in the two Freon compounds. Stoichiometry helps us understand the proportion of one substance that reacts with another to form different substances. This information is invaluable in industries like pharmaceuticals, where precise dosages are essential.

Molecular Formula

The molecular formula is like a chemical signature. It tells you exactly which atoms and how many of each are present in a molecule. For example, Freon-12's molecular formula, \(\mathrm{CCl}_{2}\mathrm{F}_{2}\), says it has two chlorine atoms, two fluorine atoms, and one carbon atom.

The molecular formula reveals not only a substance's components but also its molar mass and chemical properties. It's the starting point for many calculations in chemistry, such as the ones performed in our problem. Knowing the molecular formula allows us to work out other important features, such as the substance's behavior under different conditions and how it might interact with other chemicals.