Answer
The molecular formula for the compound is C₂H₆
Step-by-step explanation
Given:
% composition: 80.0% carbon, 20% hydrogen.
Molecular mass = 30.0 amu
What to find:
The molecular formula for the compound.
Step-by-step solution:
Assume we have 100 grams total of the substance.
Grams C: 80.0/100 x 100 g = 80.0 g
Grams H: 20/100 x 100 = 20 g
The next step is to convert the number of grams of each element into moles as shown below using the molar masses of H = 1.00784 g/mol and C = 12.011 g/mol.
Note: Mole = Mass/Molar mass.
Moles C = 80.0g/12.011 g/mol = 6.66 mol
Moles H = 20g/1.00784 g/mol = 19.84 mol
Now, let's divide the number of moles of each element by the smallest number obtained:
C = 6.66/6.66 = 1
H = 19.84/6.66 = 3
The empirical formula for the compound is CH₃
Using the molecular mass of 30.0 amu, the molecular formula is calculated as follows:
(Empirical mass)n = (Molecular mass)
(CH₃)n = 30.0
(12.011 + 3 x 1.00784)n = 30
(12.011 + 3.02352)n = 30
(15.03452)n = 30
Divide both sides by 15.03452
n = 2
Moleculare formula = (CH₃)₂ = C₂H₆
Therefore, the molecular formula for the compound is C₂H₆