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The Chemistry AS-level Thread

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Original post by Mutleybm1996
Does anyone have any advice on getting past 52/60? I can't seem to do it -.-


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get more questions right
does anybody have ideas for grade boundaries for AQA ISAs? I got a 32/50 and am trying to get an A :frown:
Original post by Mutleybm1996
Does anyone have any advice on getting past 52/60? I can't seem to do it -.-


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if this is for Chem1 - try using the notes on chemrevise (i think thats the name) - and just be able to recite every word
oh and PPs
a mark scheme for a paper I'm doing says that formation of chlorine free radicals is heterolytic bond fission. I swear its homolytic?
Original post by Wiggledinho
a mark scheme for a paper I'm doing says that formation of chlorine free radicals is heterolytic bond fission. I swear its homolytic?


It's homolytic.
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78Saab
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Original post by Silver_moon
does anybody have ideas for grade boundaries for AQA ISAs? I got a 32/50 and am trying to get an A :frown:


Look at the AQA 2013 GCE grade boundaries, but it really all depends on which ISA you did. 1398506380740.jpg

For an A you needed 45/50 for the 3T ISA
For an A you needed 38/50 for the 3X ISA

32/50 would have just given you a C in the 3X ISA

While 32/50 would have given you a U in the 3T ISA


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Any threads for edexcel chem unit 1 and 2?
Original post by L'Evil Fish
It's homolytic.


yeah thought so, mark scheme must be wrong.
Original post by Wiggledinho
a mark scheme for a paper I'm doing says that formation of chlorine free radicals is heterolytic bond fission. I swear its homolytic?


what exam board ?
Original post by pinkgorilla
what exam board ?


wasn't an exam board, just some extra questions we got given - astarexams.com
Why does Nitrogen have a lone pair of electrons? It has 5 in it's outer shell so surely it can bond 3 times as 5+3=8 so why is there a lone pair in NH3 surely it's bonded three times to the hydrogen's?

Sorry it's probably really simple


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When assigning oxidation numbers to NaClO would Na or Cl take priority?

So O is -2
Na is +1 and Cl is -1 so which would i use to determine which is +3 or +1?


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Original post by Mutleybm1996
Why does Nitrogen have a lone pair of electrons? It has 5 in it's outer shell so surely it can bond 3 times as 5+3=8 so why is there a lone pair in NH3 surely it's bonded three times to the hydrogen's?

Sorry it's probably really simple


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The nitrogen is bonded to 3 hydrogen atoms. So they share three electrons with the hydrogen, one each; which means that there is still 2 electron left on the nitrogen and that is the lone pair. 3(atoms of nitrogen bonded with hydrogen) + 3(hydrogen atoms bonded to nitrogen)+2(lone pair) = 8
Hope that made sense.
Original post by Mutleybm1996
When assigning oxidation numbers to NaClO would Na or Cl take priority?

So O is -2
Na is +1 and Cl is -1 so which would i use to determine which is +3 or +1?


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I'm not too sure on this one, but wouldn't it be O is -2, Cl +1, and Na +1
Original post by pinkgorilla
I'm not too sure on this one, but wouldn't it be O is -2, Cl +1, and Na +1


Yep
Original post by L'Evil Fish
Yep


Thanks :biggrin:
Original post by pinkgorilla
The nitrogen is bonded to 3 hydrogen atoms. So they share three electrons with the hydrogen, one each; which means that there is still 2 electron left on the nitrogen and that is the lone pair. 3(atoms of nitrogen bonded with hydrogen) + 3(hydrogen atoms bonded to nitrogen)+2(lone pair) = 8
Hope that made sense.


Oh, i was thinking of it the wrong way round! A stupid mistake, sorry, thank you :smile:
Original post by L'Evil Fish
Yep


Annoyingly the only one's we've done is the ones with two of the known oxidation numbers such as O is -2 and H is +1 in the same compound with one unknown and never two unknown so i was just wondering which would take precedence.


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Just to check: do oxidation numbers only work on empirical formulae? I made the mistake of thinking that the Oxidation number of N was +4 in N(2)H(4) whilst doing a paper today.
(edited 9 years ago)
Original post by 78Saab
Look at the AQA 2013 GCE grade boundaries, but it really all depends on which ISA you did. 1398506380740.jpg

For an A you needed 45/50 for the 3T ISA
For an A you needed 38/50 for the 3X ISA

32/50 would have just given you a C in the 3X ISA

While 32/50 would have given you a U in the 3T ISA


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Okay thank you!

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