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# A2 Chemistry help...... watch

1. Hi, Quick question I cant get my head around!

'Assume that the empirical formula of benzene is CH. What further information is needed to show that its molecular formula is C6H6? What methods do chemists use to obtain this information?'

I understand that it is a 1:1 ratio so the empirical will be the simplest form of CH but I dont know how chemists realise its 'actual' molecular formula and how they obtain this info.....

3. mass spectrometry to show the m/e peak?
4. Mass spectrometry data?
5. Mass spec will show that the molecule has a mass of 78, C1H1 has a mass of 13 and 78/13=6 so the molecular formula in 6 x CH = C6H6
6. mass spec
7. thanks for that it seems pretty obvious now lol......just one other of the many questions I had to do if thats ok:

Q3 is: An arene consists of 91.3% carbon.
a) What is the empirical formula of the arene?
b) What is the molecular formula of the arene if its molar mass is 92?
c) Draw the scructure of the arene.

so far i thought if 91.3 % C then 8.7% H but not sure if its just C and H cos u get horrible numbers......confused!!!!.com
thanks
8. (Original post by Holden)
Mass spec will show that the molecule has a mass of 78, C1H1 has a mass of 13 and 78/13=6 so the molecular formula in 6 x CH = C6H6
thanks!!....just one other question above if you could help, would be very much appreciated!!!
9. 91.3% of 92 gives mass of C, divide by 12 to get number of C
same with H using it's % and molar mass
structure should be fairly obvious once you've got that

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