Question

The Freons are a class of compounds containing carbon, chlorine, and fluorine. While they have many valuable uses, they have been shown to be responsible for depletion of the ozone in the upper atmosphere. In 1991 , two replacement compounds for Freons went into production: \(\mathrm{HFC}-134 \mathrm{a}\left(\mathrm{CH}_{2} \mathrm{FCF}_{3}\right)\) and \(\mathrm{HCFC}-124\) (CHCIFCF \(_{3}\) ). Calculate the molar masses of these two compounds.

Short answer

The molar mass of HFC-134a (CH2FCF3) is 90.03 g/mol, and the molar mass of HCFC-124 (CHCIFCF3) is 251.37 g/mol.

Step-by-step solution

Identify the elements and their atomic masses

Refer to the periodic table to find the atomic masses of the elements present in the compounds. The elements and their atomic masses are: - Carbon (C): 12.01 g/mol - Hydrogen (H): 1.01 g/mol - Chlorine (Cl): 35.45 g/mol - Fluorine (F): 19.00 g/mol - Iodine (I): 126.90 g/mol

Calculate the molar mass of HFC-134a

For HFC-134a (CH2FCF3), the molar mass can be calculated as follows: - 1 Carbon atom: 1 × 12.01 g/mol - 2 Hydrogen atoms: 2 × 1.01 g/mol - 1 Fluorine atom: 1 × 19.00 g/mol - 3 Fluorine atoms: 3 × 19.00 g/mol Now, sum all the values: Molar mass of HFC-134a = (1 × 12.01) g/mol + (2 × 1.01) g/mol + (1 × 19.00) g/mol + (3 × 19.00) g/mol

Calculate the molar mass of HCFC-124

For HCFC-124 (CHCIFCF3), the molar mass can be calculated as follows: - 1 Carbon atom: 1 × 12.01 g/mol - 1 Hydrogen atom: 1 × 1.01 g/mol - 1 Chlorine atom: 1 × 35.45 g/mol - 1 Iodine atom: 1 × 126.90 g/mol - 1 Fluorine atom: 1 × 19.00 g/mol - 3 Fluorine atoms: 3 × 19.00 g/mol Now, sum all the values: Molar mass of HCFC-124 = (1 × 12.01) g/mol + (1 × 1.01) g/mol + (1 × 35.45) g/mol + (1 × 126.90) g/mol + (1 × 19.00) g/mol + (3 × 19.00) g/mol

Finalize the molar mass calculations

Molar mass of HFC-134a = (12.01) g/mol + (2.02) g/mol + (19.00) g/mol + (57.00) g/mol = 90.03 g/mol Molar mass of HCFC-124 = (12.01) g/mol + (1.01) g/mol + (35.45) g/mol + (126.90) g/mol + (19.00) g/mol + (57.00) g/mol = 251.37 g/mol So, the molar mass of HFC-134a is 90.03 g/mol, and the molar mass of HCFC-124 is 251.37 g/mol.

Key concepts

Freons

Freons, a series of chlorofluorocarbons (CFCs), have historically played a significant role in various applications such as refrigerants, propellants in aerosol sprays, and solvents. However, these compounds are now infamous for their environmental impact, specifically their potential to deplete the stratospheric ozone layer.

Their stability was once prized, but it is this very characteristic that allows them to persist long enough to reach the upper atmosphere, where they release chlorine atoms through photodissociation. These chlorine atoms act as catalysts in the breakdown of ozone molecules, contributing to the ozone hole and increased ultraviolet radiation reaching the Earth's surface, which poses a threat to both human health and the environment.

Ozone Depletion

The depletion of the ozone layer is a significant global concern. The ozone layer, located within the stratosphere, acts as Earth's natural sunscreen by absorbing the majority of the sun's harmful ultraviolet (UV) radiation. When Freons and other CFCs reach the stratosphere, they are broken down by UV light, releasing chlorine atoms. A single chlorine atom can destroy thousands of ozone molecules before it is removed from the stratosphere, leading to increased UV radiation at ground level, which can cause skin cancer, cataracts, and have adverse effects on the environment and wildlife.

Periodic Table

The periodic table of elements is a tabular display crucial for understanding chemical properties and relationships among elements. It organizes elements by increasing atomic number and aligns them into groups and periods based on recurring chemical properties. For molar mass calculations, it serves as a reference to find atomic masses, a fundamental parameter required to calculate the molar mass of chemical compounds.

Being familiar with the periodic table allows students and chemists to quickly determine the proportionate weights of different atoms and use these figures to determine the weights of various chemical substances, as shown in the step-by-step solution for Freons and their replacements.

Atomic Mass

Atomic mass, often listed as the atomic weight on the periodic table, represents the average mass of atoms of an element, measured in atomic mass unit (amu). For an element with multiple isotopes, atomic mass is a weighted average reflecting the natural abundance of those isotopes.

In the context of the exercise, knowledge of atomic masses allows us to calculate the molar mass of chemical compounds, which is the mass of one mole of that substance. By summing the atomic masses of all atoms in the molecule, we get the molecular weight, an essential value for understanding chemical amounts and reactions. For instance, the precise calculation of the molar mass for HFC-134a and HCFC-124 uses the atomic mass of each element involved, reflecting the molecular composition of each compound.