a hydrocarbon has 7.69% hydrogen. find the molecular formula if the molecular mass is 78amu
Share
a hydrocarbon has 7.69% hydrogen. find the molecular formula if the molecular mass is 78amu
Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Convert the hydrogen percentage to moles:
Hydrogen has an atomic mass of approximately 1 g/mol.
So, 7.69% hydrogen in the compound means there are 7.69 g of hydrogen in 100 g of the compound.
Moles of hydrogen = (7.69 g / 1 g/mol) = 7.69 moles
Calculate the moles of carbon:
Since a hydrocarbon contains only carbon and hydrogen, the remaining mass must be due to carbon.
Molecular mass of the compound = 78 amu
Moles of carbon = Total moles - Moles of hydrogen
Moles of carbon = (78 amu / 1 g/mol) - 7.69 moles = 70.31 moles
Determine the ratio of hydrogen to carbon moles:
Divide the moles of hydrogen by the moles of carbon:
Hydrogen : Carbon moles = 7.69 moles : 70.31 moles
Simplify the ratio, if necessary:
Divide both the hydrogen and carbon moles by the smallest number of moles in the ratio to get a whole number ratio.
In this case, the ratio simplifies to approximately 1:9.
So, the empirical formula of the hydrocarbon is CH9