Question

The molecular formula mass was measured using a mass spectrometer. it was determined to be 331 g/mol. using the empirical formula from the question above, determine the molecular formula for the unknown compound?

Answer 1

To determine the molecular formula of a compound, divide its molar mass by the empirical formula mass to find the number of empirical formula units per molecule and multiply the subscripts of the empirical formula by this number.

Step-by-step explanation:

To determine the molecular formula of an unknown compound with a measured molar mass of 331 g/mol using its empirical formula, one needs to follow these steps:

• Calculate the empirical formula mass by summing the average atomic masses of all the atoms in the empirical formula.
• Divide the given molecular (or molar) mass by the empirical formula mass to obtain the number of empirical formula units per molecule, designated as n.
• Multiply each subscript in the empirical formula by n to get the molecular formula.

For example, if the empirical formula was found to be CH2 which has an empirical formula mass of approximately 14 g/mol, dividing 331 g/mol (the given molar mass) by 14 g/mol (the empirical formula mass) gives us a factor of about 23.64.

Since molecular formulas are represented by whole numbers, we would round to the nearest whole number, if necessary, and multiply each subscript in the empirical formula by this whole number to obtain the final molecular formula.