Problem 50 - Chemistry An Atoms First Approach

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: HFC-134a \(\left(\mathrm{CH}_{2} \mathrm{FCF}_{3}\right)\) and HCFC-124 \(\left(\mathrm{CHClFCF}_{3}\right)\). Calculate the molar masses of these two compounds.

Step-by-Step Solution

Answer

The molar mass of HFC-134a (CH₂FCF₃) is 90.03 g/mol, and the molar mass of HCFC-124 (CHClFCF₃) is 105.47 g/mol.

Step 1: Identify the molar masses of individual elements

The molar masses of individual elements are as follows (in g/mol): - Carbon (C): 12.01 - Hydrogen (H): 1.01 - Fluorine (F): 19.00 - Chlorine (Cl): 35.45

Step 2: Determine the molar mass of HFC-134a

For HFC-134a (CH₂FCF₃), there is 1 Carbon atom, 2 Hydrogen atoms, and 4 Fluorine atoms. Multiply the respective atoms by their molar masses and sum them up: HFC-134a molar mass = (1 × 12.01) + (2 × 1.01) + (4 × 19.00) = 12.01 + 2.02 + 76.00 = 90.03 g/mol

Step 3: Determine the molar mass of HCFC-124

For HCFC-124 (CHClFCF₃), there is 1 Carbon atom, 1 Hydrogen atom, 1 Chlorine atom, and 3 Fluorine atoms. Multiply the respective atoms by their molar masses and sum them up: HCFC-124 molar mass = (1 × 12.01) + (1 × 1.01) + (1 × 35.45) + (3 × 19.00) = 12.01 + 1.01 + 35.45 + 57.00 = 105.47 g/mol So, the molar mass of HFC-134a is 90.03 g/mol, and the molar mass of HCFC-124 is 105.47 g/mol.

Key Concepts

Freons

Freons have been commonly used as refrigerants, propellants, and solvents due to their low toxicity and non-flammability. However, despite these beneficial properties, Freons made up primarily of carbon, chlorine, and fluorine, have raised environmental concerns. These compounds, specifically chlorofluorocarbons (CFCs), contribute significantly to the depletion of the ozone layer in the Earth's stratosphere.

The ozone layer plays a crucial role in absorbing much of the Sun's harmful ultraviolet radiation. When Freons enter the atmosphere, they eventually reach the ozone layer. Here, under the influence of ultraviolet (UV) light, they release chlorine atoms. A single chlorine atom can destroy thousands of ozone molecules, highlighting the environmental risk these compounds pose.

Efforts to curtail the use of Freons began with international agreements like the Montreal Protocol, aiming to reduce and eventually phase out the production and usage of ozone-depleting substances.

HFC-134a

HFC-134a, chemically known as \(\mathrm{CH}_{2} \mathrm{FCF}_{3}\), represents a newer wave of refrigerants replacing traditional CFCs and certain HCFCs. One of the main reasons for adopting HFC-134a is that it does not contain chlorine, a key player in ozone depletion. This makes HFC-134a a more environmentally friendly option compared to its predecessors.

When calculating the molar mass of HFC-134a, we consider the components:

• 1 Carbon (C) atom: 12.01 g/mol
• 2 Hydrogen (H) atoms: 2 \( \times \) 1.01 = 2.02 g/mol
• 4 Fluorine (F) atoms: 4 \( \times \) 19.00 = 76.00 g/mol

Adding these values gives us a total molar mass of 90.03 g/mol.

This calculation is crucial for determining how HFC-134a behaves in different conditions and applications.

HCFC-124

HCFC-124, or \(\mathrm{CHClFCF}_{3}\), serves as another slightly older alternative to traditional Freons. This compound was developed to decrease the potential for ozone depletion but still contains a chlorine atom. Therefore, HCFC-124 contributes less to ozone depletion than CFCs, but more than HFC-134a.

In terms of calculating the molar mass, here are the component parts:

• 1 Carbon (C) atom: 12.01 g/mol
• 1 Hydrogen (H) atom: 1.01 g/mol
• 1 Chlorine (Cl) atom: 35.45 g/mol
• 3 Fluorine (F) atoms: 3 \( \times \) 19.00 = 57.00 g/mol

Combining these gives us a molar mass of 105.47 g/mol.

Understanding the molar mass helps in assessing the environmental impact and efficiency of HCFC-124.

Ozone Depletion

Ozone depletion is a critical environmental issue primarily attributed to the release of ozone-depleting substances, such as certain Freons (CFCs) and even HCFCs. The ozone layer acts as Earth's shield against ultraviolet (UV) radiation. Without it, increased UV radiation can reach the surface, posing risks to human health, wildlife, and plant life.

Compounds responsible for ozone depletion typically contain chlorine and bromine. They are stable in the atmosphere, allowing them to gradually travel up into the stratosphere, where they break down under UV light. This process releases the destructive chlorine or bromine atoms. Each of these atoms can destroy numerous ozone molecules, leading to thinning of the ozone layer, known as ozone holes.

Efforts like the Montreal Protocol aim to mitigate this damage by phasing out the production and use of ozone-depleting chemicals. By understanding molar masses and chemical compositions of substitutes like HFCs, we can develop less harmful alternatives that minimize environmental impact.