Environmental Science: Numerical Questions – Conversion CFC to Formula

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Type I - Number to Formula

1. Chemical formula for CFC-113 is

  1. CCl2F2
  2. CCl3F3
  3. C2 Cl3F3
  4. CCl2F3

Answer: (C) C2 Cl3F3

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 CCl2F2CF3?

  1. 115
  2. 132
  3. 134
  4. 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.

CCl2F2CF3 = C2F5Cl2

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:

  1. CF2ClBr
  2. CCl2FBr
  3. CCl2F2
  4. CBr2ClF

Answer: CF2ClBr

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

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