Determine the molecular formula of a compound that has a molar mass of [tex]122.11 \, g/mol[/tex] and an empirical formula of [tex]C_2H_5O_2[/tex].

A. [tex]C_2H_5O_2[/tex]
B. [tex]C_6H_{15}O_6[/tex]
C. [tex]C_3H_7O_3[/tex]
D. [tex]C_4H_{18}O_4[/tex]
E. [tex]C_8H_{20}O_8[/tex]



Answer :

To determine the molecular formula of a compound, we need to follow these steps:

1. Calculate the molar mass of the empirical formula:
The empirical formula given is [tex]\( C_2H_5O_2 \)[/tex].
- Molar mass of Carbon (C): 12.01 g/mol
- Molar mass of Hydrogen (H): 1.008 g/mol
- Molar mass of Oxygen (O): 16.00 g/mol

First, we calculate the molar mass for [tex]\( C_2H_5O_2 \)[/tex]:
[tex]\[ \text{Molar mass of } C_2H_5O_2 = (2 \times 12.01) + (5 \times 1.008) + (2 \times 16.00) \][/tex]
[tex]\[ = 24.02 + 5.04 + 32.00 = 61.06 \, \text{g/mol} \][/tex]

2. Determine the ratio of the compound’s molar mass to the empirical formula’s molar mass:
The molar mass of the compound provided is 122.11 g/mol. Thus we find the ratio:
[tex]\[ \text{Ratio} = \frac{\text{Compound's molar mass}}{\text{Empirical formula's molar mass}} = \frac{122.11}{61.06} \approx 2.00 \][/tex]

3. Determine the molecular formula by multiplying the subscripts in the empirical formula by the ratio:
The empirical formula is [tex]\( C_2H_5O_2 \)[/tex], and the ratio is approximately 2. So, multiply each subscript in the empirical formula by this ratio:
- Carbon atoms: [tex]\( 2 \times 2 = 4 \)[/tex]
- Hydrogen atoms: [tex]\( 5 \times 2 = 10 \)[/tex]
- Oxygen atoms: [tex]\( 2 \times 2 = 4 \)[/tex]

Therefore, the molecular formula is [tex]\( C_4H_{10}O_4 \)[/tex].

4. Match the determined molecular formula with the given options:
Among the provided options, the one that matches [tex]\( C_4H_{10}O_4 \)[/tex] is:

[tex]\[ C_4H_{10}O_4 \][/tex]

Thus, the molecular formula of the compound is [tex]\( C_4H_{10}O_4 \)[/tex].