# Environmental Science: Numerical Questions – Conversion CFC to Formula

Dr. Manishika Jain- Join online Paper 1 intensive course. Includes tests and expected questions.

## Type I - Number to Formula

1. Chemical formula for CFC-113 is

- CC
*l*2F2 - CC
*l*3F3 - C2 C
*l*3F3 - CC
*l*2F3

Answer: (C) C2 C*l*3F3

Explanation:

- Step 1 – Add 90
- Step 2 – Calculate the number of Carbon atoms, Hydrogen atoms and Fluorine atoms
- Step 3 – write the formula using the C, H & F atoms

Step 1: 90 + 113 = 203

Step 2:

- Number of Carbon atoms = 2
- Number of Hydrogen atoms = 0
- Number of Fluorine atoms = 3

Step 3: The CFC formula will be C2F3Cl3

## Type II – Formula to Number

2. What is the CFC number for the halocarbon CCl_{2}F_{2}CF_{3}?

- 115
- 132
- 134
- 143

Answer: (A) 115

Explanation:

To calculate the CFC number:

- Consider the formula in the number of carbon, hydrogen , fluorine (do not include chlorine)
- Subtract the number with 90
- The number obtained thereafter is the formula.

CCl_{2}F_{2}CF_{3} = C_{2}F_{5}Cl_{2}

Step 1:

- Number of Carbon atoms = 2
- Number of Hydrogen atoms = 0
- Number of Fluorine atoms = 5

So, the number obtained is 205 (as we do not consider Chlorine atoms)

Step 2: 205 - 90 = 115

Step 3: The CFC number will be CFC 115

## Type III – Formula for Halons

3. The halon H − 1211 has the following chemical composition:

- CF
_{2}ClBr - CCl
_{2}FBr - CCl
_{2}F_{2} - CBr
_{2}ClF

Answer: CF_{2}ClBr

Each halon has a number system of abcd where.

a - Is the number of carbon atoms

b - The number of fluorine atoms

c - The number of chlorine atoms

d - The number of bromine atoms

-Mayank