Question

Fumaric acid, which occurs in many plants, contains, by mass, 41.4% carbon, 3.47% hydrogen, and 55.1%
oxygen. A 0.050-mol sample of this compound weighs 5.80 g. The molecular formula of this compound is

Answer 1

Take a 100 g sample. That gives you
41.4 g C
3.47 g H
55.1 g O
Convert each of the grams to moles. moles = g/molar mass.
Then determine the ratio of the elements to the smallest (found by dividing all of the numbers by the smallest number of moles). That gives the empirical formula.
Since moles = g/molar mass, the second part of the problem allows you to determine the molar mass.
Divide molar mass/empirical formula mass to determine the number of empirical formula units in the mole.