Molecular formula

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Created by: Rachael
Created on: 17-10-10 15:36

Molecular Formula

Shows the actual number of atoms of each element in a molecule.
Example: a compound contains 40.00% Carbon, 6.73% hydrogen and 53.27% oxygen by mass.
Determine the empirical formula:
C= 40/12.01=3.33
H=6.73/1.01=6.66
O=53.27/16.00= 3.33
Ratio is 3.33:6.66:3.33 = 1:2:1
therefore empirical formula is CH20
Molecular formula can be obtained from the empirical formula if the molar mass of the compound is also known
CH2O = 12.01+ 1.01+ 1.01+ 16.00 = 30
Mr = 60
Molecular formula is C2H4O2

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Comments

Mel Godfrey

Report Wed 11th May, 2011 @ 11:13

what does mr mean? how do u get mr = 60, after working out that CH2O = 30?

Amritpal Mundra

Report Mon 16th May, 2011 @ 21:10

Mel Godfrey wrote:

mr is molecular mass

Derryl

Report Fri 20th May, 2011 @ 12:09

where do you get the 12.01 from?!

Rachael

Report Fri 20th May, 2011 @ 18:13

Mel Godfrey: if you know what the Mr is, in this case it is 60, you can then work out what the molecular formula is. The mr= 60 would have been given in the question

Derryl: 12.01 is the atomic mass of carbon, from the periodic table

William

Report Tue 22nd January, 2013 @ 11:40

inncorrect