Question

a lab technician knows that the empirical formula of a molecule is ch₂. he uses a mass spectrometer to determine the molar mass of the compound. the test results show that the molar mass is 56.1 g/mol.
what is its molecular formula?
a. ch₂
b. c₂h₄
c. c₃h₆
d. c₄h₈

Explanation:

Step1: Calculate the empirical formula mass

The empirical formula is \(CH_2\). The atomic mass of \(C = 12.01\space g/mol\) and \(H= 1.01\space g/mol\).
The empirical formula mass \(M_{empirical}=(1\times12.01)+(2\times1.01)=14.03\space g/mol\)

Step2: Find the ratio \(n\)

The molar mass \(M = 56.1\space g/mol\).
We use the formula \(n=\frac{M}{M_{empirical}}\)
\(n=\frac{56.1}{14.03}\approx4\)

Step3: Determine the molecular formula

Multiply the sub - scripts in the empirical formula \(CH_2\) by \(n = 4\)
The molecular formula is \(C_{1\times4}H_{2\times4}=C_4H_8\)

Answer:

D. \(C_4H_8\)