Question

A compound contains, by mass, 87.5% nitrogen and 12.5% hydrogen. Its molecular weight is found to be 32 g/mol. What is its molecular formula?

Answer 1

The molecular formula of the compound with 87.5% nitrogen and 12.5% hydrogen by mass and a molecular weight of 32 g/mol is N2H4.

Step-by-step explanation:

To determine the molecular formula of a compound with 87.5% nitrogen and 12.5% hydrogen by mass and a molecular weight of 32 g/mol, we first calculate the molar amounts of each element in the compound. For nitrogen, which has an atomic mass of 14 g/mol (since it's typically N2, we use 14 g/mol for the atomic mass of N), we have:

• (87.5 g / 14 g/mol) = 6.25 mol N

For hydrogen, with an atomic mass of 1 g/mol:

• (12.5 g / 1 g/mol) = 12.5 mol H

The simplest whole number ratio is found by dividing by the smallest number of moles:

• N = 6.25 / 6.25 = 1
• H = 12.5 / 6.25 = 2

So, the empirical formula is NH2. To find the molecular formula, we divide the molecular weight of the compound by the molecular weight of the empirical formula (14 for N and 1 for each H, totaling 16 g/mol for NH2):

• 32 g/mol / 16 g/mol = 2

Therefore, the molecular formula is (NH2)2 or N2H4, as multiplying the empirical formula by 2 gives the correct molecular weight of 32 g/mol.