What is the molecular formula of a compound that is composed of 0.186 g C, 0.0390 g H and 0.108 g N that has a molar mass of 129 g/mol?

Question

Quizplus · Accepted Answer

1. Calculate the moles of each element using their given masses and molar masses:
moles of C = 0.186 g / 12.01 g/mol = 0.0155 mol
moles of H = 0.0390 g / 1.01 g/mol = 0.0386 mol
moles of N = 0.108 g / 14.01 g/mol = 0.0077 mol

2. Find the lowest whole number mole ratio by dividing each number of moles by the smallest number of moles:
0.0155 mol / 0.0077 mol = 2.01 (rounded to 2)
0.0386 mol / 0.0077 mol = 5.02 (rounded to 5)
0.0077 mol / 0.0077 mol = 1

3. Write the empirical formula using the whole number mole ratios as subscripts: C2H5N

4. Calculate the empirical formula mass:
(2 x 12.01 g/mol) + (5 x 1.01 g/mol) + (1 x 14.01 g/mol) = 71.08 g/mol

5. Calculate the factor by which the empirical formula mass must be multiplied to equal the given molar mass:
molar mass / empirical formula mass = 129 g/mol / 71.08 g/mol ≈ 1.816

6. Multiply the empirical formula subscripts by the factor calculated in step 5 to get the molecular formula: (C2H5N) x 1.816 ≈ C4.4H9.1N

What Is the Molecular Formula of a Compound That Is