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Chemistry unit 1 question-exam tomorrow!

ImageUploadedByStudent Room1400753664.277018.jpg
The question is "deduce the empirical formula of graphane". I thought it was C4H as drawing it out, one Carbon atom is bonded to 3 other carbons and one hydrogen. But it's CH and I really don't get why!!!


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Original post by jazzie14
ImageUploadedByStudent Room1400753664.277018.jpg
The question is "deduce the empirical formula of graphane". I thought it was C4H as drawing it out, one Carbon atom is bonded to 3 other carbons and one hydrogen. But it's CH and I really don't get why!!!


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if you look more carefully at the diagram you'll see that every carbon atom is bonded to one hydrogen atom ...
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Avatar for jazzie14
jazzie14
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Original post by charco
if you look more carefully at the diagram you'll see that every carbon atom is bonded to one hydrogen atom ...

yes but it also says every carbon atom is also bonded to 3 other carbon atoms?
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Avatar for person287
person287
yeah but each Carbon can therefore only have one hydrogen on it, as 3 bonds are 'used', as it can form a maximum of 4 bonds, so each Carbon has one Hydrogen on it, so the simplest whole number ratio of atoms in the giant molecule/lattice is 1:1, so CH
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MSamuel
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anyone know what could possibly come up tomorrow? I'm really not looking forward to it, chemistry unit 1 has screwed me over so many times.
Original post by jazzie14
yes but it also says every carbon atom is also bonded to 3 other carbon atoms?


I don't know if this is right but, the question says that each carbon atom is bonded to 3 other carbon atoms, therefore c=4. It also says that each carbon atom is bonded to a hydrogen atom and because there are 4 carbon atoms, h=4. An emperical formula is the simplest whole number ration, so if you divide both the number of carbons and the number of hydrogens by 4, you end up with c=1 and h=1. Therefore the emperical formula is CH.

Also if you look at the picture you can see that there is a light grey ball on every dark grey ball which suggests the molecular formula is C4H4, which means that the emperical formula should be CH.

sorry for the long winded reply, I wanted to explain thoroughly. Oh and a MASSIVE disclaimer, I'm not sure if I'm right, so if anyone wants to correct me feel free! :smile:
Reply 6
Avatar for Pigster
Pigster
20
Original post by HalinaAkhtar
the molecular formula is C4H4


Careful, you're wrong on two counts.
Ah this question, I got 59/60 in my mock and this was the very question that I slipped up on!

Yes it's really trick and you can be confsed and put CH4 (which is what I did), especially after the questions leading on the that one. However if you look closely it's actually CH, try using a pencil and grouping them, you'll see that one carbon can only group with one hydrogen.
Reply 8
Avatar for abbielucy
abbielucy
what exam board is this with?

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