Question

A compound of carbon and hydrogen contains 92.3 percent c and has a molar mass of 78.1g/mol. What is its molecular

Answer 1

Answer:

C₆H₆

Explanation:

We need to find the molecular formula of a compound of carbon (C) and hydrogen (H), so what we need to find out is the number of atoms of C and of  H in the molecule. We know:

• molar mass = 78.1 g/mol
• C% = 92.3% = 92.3 g C / 100 g compound

So, in 1 mol of compound, 92.3% of the mass corresponds to Carbon:

mass of C / mol of compound = molar mass × C% = 78.1 g/mol × 92.3/100 = 72.1 g/mol

moles of C = mass C / molar mass C = 72.1 g / 12.011 g/mol

moles of C = 6 moles of C per mol of compound

If 72.1 g in a mol of compound are Carbon atoms, the difference between the molar mass and the mass of Carbon atoms will correspond to H atoms in 1 mol of compound:

mass of H / mol of compound = molar mass - mass of C/mol

mass of H = 78.1 g / mol - 72.1 g /mol = 6.0 g/mol of compound

moles of H = mass H / molar mass H = 6.0 g / 1.008 g/mol

moles of H = 6.0 moles of H per mol of compound

So one mol of compound has 6 moles of C and 6 moles of H.

The molecular formula is then written as C₆H₆