Problem 100 - Chemistry The Molecular Science

Question

Polytetrafluoroethylene (Teflon) is made by first treating HF with chloroform, then cracking the resultant difluorochloromethane. $$ \begin{array}{c} \mathrm{CHCl}_{3}+2 \mathrm{HF} \longrightarrow \mathrm{CHClF}_{2}+2 \mathrm{HCl} \\ 2 \mathrm{CHClF}_{2} \frac{\text { high }}{T} \mathrm{~F}_{2} \mathrm{C}=\mathrm{CF}_{2}+2 \mathrm{HCl} \\ \mathrm{F}_{2} \mathrm{C}=\mathrm{CF}_{2} \stackrel{\text { peroxide catalyst }}{\longrightarrow} \text { Teflon } \end{array} $$ You want to make \(1.0 \mathrm{~kg}\) Teflon. Calculate the mass of chloroform and HF required to make the starting material, \(\mathrm{CHClF}_{2}\). (Although it is not realistic, assume that each reaction step proceeds to a \(100 \%\) yield.)

Step-by-Step Solution

Answer

2.3876 kg of chloroform and 0.8004 kg of HF are needed.

Step 1: Determine Moles of Teflon Needed

First, we need to determine how many moles of Teflon ( ext{C}_2 ext{F}_4) are required for 1.0 kg. The molar mass of Teflon is approximately 100.02 g/mol. Thus, the number of moles is calculated by dividing the mass by the molar mass: \[ \text{Moles of Teflon} = \frac{1000 \text{ g}}{100.02 \text{ g/mol}} = 10.0 \text{ mol.} \]

Step 2: Relate Teflon to CHClF2 Production

From the reaction \(2 \, \text{CHClF}_2 \rightarrow \text{C}_2\text{F}_4 + 2 \text{HCl}\), we see that 2 moles of \text{CHClF}_2 are needed to produce 1 mole of Teflon. Therefore, to make 10.0 moles of Teflon, 20.0 moles of \text{CHClF}_2 are required.

Step 3: Calculate Moles of Chloroform Required

The chemical equation \(\text{CHCl}_3 + 2 \text{HF} \rightarrow \text{CHClF}_2 + 2 \text{HCl}\) shows that 1 mole of \text{CHCl}_3 is required to produce 1 mole of \text{CHClF}_2. Thus, 20.0 moles of chloroform are required.

Step 4: Calculate Mass of Chloroform Needed

The molar mass of chloroform (\text{CHCl}_3) is approximately 119.38 g/mol. Therefore, the mass required is: \[ \text{Mass of CHCl}_3 = 20.0 \text{ mol} \times 119.38 \text{ g/mol} = 2387.6 \text{ g} = 2.3876 \text{ kg} \]

Step 5: Calculate Moles of HF Required

According to the equation \(\text{CHCl}_3 + 2 \text{HF} \rightarrow \text{CHClF}_2 + 2 \text{HCl}\), 2 moles of \text{HF} are needed per mole of \text{CHClF}_2. Therefore, 40.0 moles of \text{HF} are needed for 20.0 moles of \text{CHClF}_2.

Step 6: Calculate Mass of HF Needed

The molar mass of HF is approximately 20.01 g/mol. Therefore, the mass of HF needed is: \[ \text{Mass of HF} = 40.0 \text{ mol} \times 20.01 \text{ g/mol} = 800.4 \text{ g} = 0.8004 \text{ kg} \]

Key Concepts

Polytetrafluoroethylene Synthesis

Polytetrafluoroethylene (commonly known as Teflon) is a high-performance plastic with unique non-stick properties. Its synthesis involves a multi-step chemical process starting from chloroform (\( \text{CHCl}_3 \)) and hydrofluoric acid (HF). The process can be broken into several key reactions:

• First, chloroform reacts with HF to form difluorochloromethane (\( \text{CHClF}_2 \)) and hydrochloric acid (\( \text{HCl} \)).
• Next, \( \text{CHClF}_2 \) is cracked at high temperatures to produce tetrafluoroethylene (\( \text{C}_2\text{F}_4 \)), the monomer of Teflon.
• Finally, in the presence of a peroxide catalyst, \( \text{C}_2\text{F}_4 \) polymerizes to form Teflon.

These reactions highlight the transformation from simple starting materials to the complex polymer structure that gives Teflon its durable and non-stick qualities.

Molar Mass Calculation

Understanding how to calculate molar mass is crucial in stoichiometry. Molar mass allows us to convert between grams of a substance and moles, which are used in chemical reactions.
To find the molar mass of a compound:

• Add the atomic masses of all atoms in the molecule. For example, the molar mass of Teflon (\( \text{C}_2\text{F}_4 \)) is calculated by adding carbon and fluorine atomic masses: \( 2 \times 12.01 \text{ g/mol} + 4 \times 19.00 \text{ g/mol} \approx 100.02 \text{ g/mol} \).

This calculation ensures you know the amount of substance you are working with in a reaction. It’s a fundamental step in determining how much starting material is needed.

Reaction Yield Assumptions

In real-world chemistry, reaction yields are rarely 100% due to side reactions and losses. However, assuming a 100% yield simplifies initial calculations and helps in understanding the theoretical possibilities of a reaction.
In this scenario, assuming each step in the Teflon synthesis goes to completion:

• For every mole of \( \text{CHClF}_2 \) produced, one mole of chloroform and two moles of HF are consumed.
• This allows for straightforward calculations of the required reactants to produce a desired amount of product.

While idealized, this assumption helps in grasping stoichiometric relationships before considering more complex reaction conditions.