Questions: The molecular weight of a compound is 140 g/mol. If the empirical formula is C4H6O, what is the molecular formula?

Solution Steps

First, we need to calculate the empirical formula weight of the compound with the empirical formula \( \text{C}_4\text{H}_6\text{O} \).

• Carbon (C): \( 4 \times 12.01 \, \text{g/mol} = 48.04 \, \text{g/mol} \)
• Hydrogen (H): \( 6 \times 1.008 \, \text{g/mol} = 6.048 \, \text{g/mol} \)
• Oxygen (O): \( 1 \times 16.00 \, \text{g/mol} = 16.00 \, \text{g/mol} \)

Adding these together gives the empirical formula weight: \[ 48.04 + 6.048 + 16.00 = 70.088 \, \text{g/mol} \]

The molecular weight of the compound is given as 140 g/mol. We calculate the ratio of the molecular weight to the empirical formula weight: \[ \text{Ratio} = \frac{140 \, \text{g/mol}}{70.088 \, \text{g/mol}} \approx 2 \]

Since the ratio is approximately 2, the molecular formula is twice the empirical formula. Therefore, the molecular formula is: \[ \text{C}_{4 \times 2}\text{H}_{6 \times 2}\text{O}_{1 \times 2} = \text{C}_8\text{H}_{12}\text{O}_2 \]

Final Answer