Question

Vapour density of a compound is \(26\). It contains carbon and hydrogen atoms in the ratio \(1:1\). Its molecular formula is

• A. \(CH\)
• B. \(C_2H_2\)
• C. \(C_4H_4\)
• D. \(C_6H_6\)

Hint:

Steps to find molecular formula:
Calculate molar mass using vapour density
Determine empirical formula from atomic ratio
Find multiplying factor \(n = \dfrac{M}{\text{EFM}}\)

Answer 1

The Correct Option is C

Step 1: Vapour density (VD) is related to molar mass \(M\) as: \[ M = 2 \times \text{VD} \] \[ M = 2 \times 26 = 52 \]
Step 2: Given atomic ratio of carbon and hydrogen is \(1:1\). Hence, the empirical formula is: \[ CH \]
Step 3: Empirical formula mass of \(CH\): \[ 12 + 1 = 13 \]
Step 4: Determine the molecular formula factor: \[ n = \frac{\text{Molecular mass}}{\text{Empirical formula mass}} = \frac{52}{13} = 4 \]
Step 5: Molecular formula: \[ (CH)_4 = C_4H_4 \]