Select the correct answer.

A compound has a molecular weight of 112.124 atomic mass units and the empirical formula [tex]$C_3 H_4 O$[/tex]. What is the molecular formula of the compound? Use the periodic table to help you.

A. [tex]$C_6 H_8 O$[/tex]
B. [tex][tex]$C_9 H_{12} O_3$[/tex][/tex]
C. [tex]$C_8 H_4 O_2$[/tex]
D. [tex]$C_4 H_8 O_2$[/tex]
E. [tex][tex]$C_6 H_8 O_2$[/tex][/tex]



Answer :

To determine the molecular formula of the compound given its empirical formula and molecular weight, we need to follow a series of steps:

1. Calculate the empirical formula weight: This is the sum of the atomic weights of all atoms in the empirical formula [tex]\(C_3H_4O\)[/tex].

- Carbon (C) has an atomic weight of 12.011.
- Hydrogen (H) has an atomic weight of 1.008.
- Oxygen (O) has an atomic weight of 16.00.

Using these atomic weights, the empirical formula weight can be calculated as follows:

[tex]\[ 3 \times 12.011 + 4 \times 1.008 + 16.00 \][/tex]

[tex]\[ = 36.033 + 4.032 + 16.00 \][/tex]

[tex]\[ = 56.065 \text{ amu} \][/tex]

2. Determine the ratio of the molecular weight to the empirical formula weight:

The given molecular weight is 112.124 amu. We divide the molecular weight by the empirical formula weight:

[tex]\[ \text{ratio} = \frac{112.124}{56.065} \][/tex]

[tex]\[ \approx 2 \][/tex]

3. Calculate the molecular formula:

The molecular formula is [tex]\(n\)[/tex] times the empirical formula, where [tex]\(n\)[/tex] is the ratio we just calculated (rounded to the nearest integer, which is 2). Therefore, we multiply each subscript in the empirical formula [tex]\(C_3H_4O\)[/tex] by 2:

[tex]\[ \begin{aligned} C &: 3 \times 2 = 6 \\ H &: 4 \times 2 = 8 \\ O &: 1 \times 2 = 2 \end{aligned} \][/tex]

Thus, the molecular formula is [tex]\(C_6H_8O_2\)[/tex].

4. Verify among given options:

We need to find which option matches this molecular formula [tex]\(C_6H_8O_2\)[/tex]:

- Option A: [tex]\(C_6H_8O\)[/tex]
- Option B: [tex]\(C_9H_{12}O_3\)[/tex]
- Option C: [tex]\(C_8H_4O_2\)[/tex]
- Option D: [tex]\(C_4H_8O_2\)[/tex]
- Option E: [tex]\(C_6H_8O_2\)[/tex]

The correct match is Option E: [tex]\(C_6H_8O_2\)[/tex].

Therefore, the molecular formula of the compound is [tex]\(C_6H_8O_2\)[/tex], and the correct answer is:

Option E: [tex]\(C_6H_8O_2\)[/tex]