Question

6. An unknown compound is analyzed and found to consist of 49% carbon, 2.7

% hydrogen, and 48.2 % chlorine. If the molecular mass of the compound is 150,
what is the molecular formula of the compound?

Answer 1

Molecular formula = C₆H₄Cl₂

Step-by-step explanation:

Given data:

Percentage of hydrogen = 2.7%

Percentage of carbon = 49%

Percentage of chlorine = 48.2%

Molar mass of compound = 150 g/mol

Molecular formula = ?

Solution:

Number of gram atoms of H = 2.7 / 1.01 = 2.67

Number of gram atoms of Cl = 48.2 / 16 = 1.36

Number of gram atoms of C = 49 / 12 = 4.08

Atomic ratio:

C : H : Cl

4.08/ 1.36 : 2.67/1.36 : 1.36/1.36

3 : 2 : 1

C : H : Cl = 3 : 2 : 1

Empirical formula is C₃H₂Cl.

Molecular formula:

Molecular formula = n (empirical formula)

n = molar mass of compound / empirical formula mass

Empirical formula mass = 12×3 + 1.01 ×2 + 35.5 = 73.52 g/mol

n = 150 / 73.52

n = 2

Molecular formula = n (empirical formula)

Molecular formula = 2 (C₃H₂Cl)

Molecular formula = C₆H₄Cl₂