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***2013 LC Chemistry Before/After***
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outnumbered wrote: »What the hell is VSEPR?????
Valence Shell Electron Pair Repulsion Theory
Bond pairs lone pairs angles pyramidal linear and so on and so on
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outnumbered wrote: »What the hell is VSEPR?????
Calm! Its Valence Shell Electron Pair Repulsion theory....
Just states that the shape of a molcule depends on the number of lone pairs in the outer shell of the central atom
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outnumbered wrote: »What the hell is VSEPR?????
Valence shell electron pair repulsion theory or something. It's about what shape the molecule will be i.e. 2 bond pairs, 2 lone pairs V-Shaped, 3 bond pairs 1 lone pair pyramidal. I think that's it anyway.
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[Deleted User] wrote: »Oh definitely! I'm not saying that there's not enough time. Just with the people in my class (not sure about anyone here) they just don't understand Chemistry! Even if they had marking schemes they aren't able to know what they're actually writing. One of them got 9% in the mock after spending 3 hours in the exam.
So if you're in that situation focus on the chapters you understand!
Woah 9%.. There's this guy in my class who comes out of every exam saying "That actually went very good. I'll be expecting at least a C". A week after, out come the results...F's all round. He lets on he's so intelligent. Just before the mocks he was finally persuaded by our Chem teacher to move to ordinary level after various replies back to her such as: "But I'm well able for a C in higher". Turn out he got 19% in ordinary level Chemistry in the mocks.0 -
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Woah 9%.. There's this guy in my class who comes out of every exam saying "That actually went very good. I'll be expecting at least a C". A week after, out come the results...F's all round. He lets on he's so intelligent. Just before the mocks he was finally persuaded by our Chem teacher to move to ordinary level after various replies back to her such as: "But I'm well able for a C in higher". Turn out he got 19% in ordinary level Chemistry in the mocks.
I know I guy like that.
8% in a physics mock and something similar in maths, battled with the teachers for ages before finally dropping down!0 -
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You know in the preparation of ethanoic acid experiment, what would you say is "the function of reflux" ? Would it be right to just say that it ensures that the ethanol is fully oxidised ? I never understood anything about reflux in class. :pac:
Returns ethanal to the reaction flask so that it is further oxidised to ethanoic acid, ensures that reaction goes to completion. 0 -
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outnumbered wrote: »Returns ethanal to the reaction flask so that it is further oxidised to ethanoic acid, ensures that reaction goes to completion.Scuid Mhór wrote: »The reaction mixture is refluxed to ensure a fast reaction and a more complete oxidation from ethanol to ethanoic acid.
Thank ye !
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Isn't prevents loss of vapour essentially the same thing as it allowing ethanol/ethanal that condenses to return to the flask to undergo further oxidation? :P
It does prevent loss of vapour. But you MUST say returns them to the reaction flask for further oxidation to ethanoic acid. Whatever the technicalities are you still need this! 0 -
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Lollipops13 wrote: »please can someone tell me how you know if an equilibrium reaction is exo or endo?! I know if it gives -54 or something like I know what it is if given in the question but when its not given how am I supposed to know!?
When you heat, the endothermic reaction takes place. So if you are told that you heated it, and it went from green to yellow i.e. reverse you know the backwards reaction is endo and the forward must be exo. 0 -
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Ok this is really easy...Lollipops13 wrote: »please can someone tell me how you know if an equilibrium reaction is exo or endo?! I know if it gives -54 or something like I know what it is if given in the question but when its not given how am I supposed to know!?
If you are given an equation you are told the forward reaction is -54 this means the forward reaction is EXOthermic.
How you know is the minus sign....think of it like if something EXits it gets taken away therefore it is a minus. Releate the EX in EXOthermic to EXit... in Exothermic reactions heat EXits...
So if you want to increase/support the forward reaction which is exothermic you should take away the heat so that more heat will EXit the reaction to replace the heat taken away by cooling.
If the forward reaction is a + it is endothermic, therefore heat is taken in...how you support/encourage the forward endothermic reaction is to add more heat...
If you think of it like this...that in the endothermic reaction heat is the fuel
In every equilibrium reaction if the forward reaction is EXothermic (heat is produced/heat exits -) then the back reaction is going to be endothemic (+ ie takes in heat!)
Sorry didnt read your question properly...outnumbered hit the nail on the head
If you would like more help on this topic pm me im more tha happy to help0 -
lizardspock wrote: »What videos??
Apparently it was "illegal" to actually carry out these experiments in schools...so they sent out videos demonstrating them...also...theyre not on the course next year at least ethanoic isnt to my knowledge so
hot topic but theyre so easy! 0 -
MarieCurie22 wrote: »Apparently it was "illegal" to actually carry out these experiments in schools...so they sent out videos demonstrating them...also...theyre not on the course next year at least ethanoic isnt to my knowledge so hot topic but theyre so easy!
Yeah the sodium dichromate was the problem, carcinogenic or something I think. I'd love if ethanoic or ethanal came up though, theyre grand plus handy enough calculations. Don't actually know why I asked, just being nosy + looking for anything to distract me from accounting!:P0 -
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A song or something? Anyone? Anyone? 
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