Question 4.16: Calculating a Molecular Formula from an Empirical Formula an...
Calculating a Molecular Formula from an Empirical Formula and Molar Mass
Butanedione—a main component responsible for the smell and taste of butter and cheese—contains the elements carbon, hydrogen, and oxygen. The empirical formula of butanedione is C_2H_3O, and its molar mass is 86.09 g/mol. Find its molecular formula.
SORT You are given the empirical formula and molar mass of butanedione and asked to find the molecular formula.
GIVEN: empirical formula = C_2H_3O
molar mass = 86.09 g/mol
FIND: molecular formula
STRATEGIZE A molecular formula is always a whole-number multiple of the empirical formula. Divide the molar mass by the empirical formula mass to determine the whole number.
molecular formula = empirical formula × n
n=\frac{molar \ mass}{empirical \ formula \ molar \ mass}
SOLVE Calculate the empirical formula mass. Divide the molar mass by the empirical formula mass to find n. Multiply the empirical formula by n to obtain the molecular formula.
empirical formula molar mass
= 2(12.01 g/mol) + 3(1.008 g/mol) + 16.00 g/mol = 43.04 g/mol
molecular formula = C_2H_3O \times 2 = C_4H_6O_2
CHECK Check the answer by calculating the molar mass of the formula as follows:
4(12.01 g/mol) + 6(1.008 g/mol) + 2(16.00 g/mol) = 86.09 g/mol
The calculated molar mass is in agreement with the given molar mass.