AQA CHEM1: 15th May 2012

Reply 40

sidra111

1

Original post by Sharyn

Do you have the CHEM2 jan 2012 paper and markscheme by any chance?

yes please, could u upload chem 2 2012 paper :smile:

Reply 41

sach21sk

Hi, does anyone know if the possibility of carbon dating questions/calculations will come up at all? I can't find it in the spec but there's a bit in the book about it :tongue:

Thanks

Reply 42

juliewho

13

Will be my third time sitting this exam, i'm taking it alongside CHEM5 to try and pick up a few UMS to make it easier to get an A overall. In my last two sittings I seem to be stuck stubbornly on a mid-B, so third time lucky :redface:

Reply 43

mynamee

OP

10

Original post by juliewho

Will be my third time sitting this exam, i'm taking it alongside CHEM5 to try and pick up a few UMS to make it easier to get an A overall. In my last two sittings I seem to be stuck stubbornly on a mid-B, so third time lucky :redface:

Hoping for an A too in this unit, CHEM2 for me is definitely not going to end well...

Reply 44

juliewho

13

Original post by mynamee

Hoping for an A too in this unit, CHEM2 for me is definitely not going to end well...

I don't remember much of CHEM2, just that there were lots of organic routes. Try to memorise them if you do nothing else, because you're guaranteed one or two. My major problem in chemistry is maths, so I did a lot better on CHEM2 :tongue:

If you have to resit CHEM2, do it in January with CHEM4, because you have to know all the organic from 2 in 4 anyway. Good luck :smile:

Reply 45

cuckoo99

13

looking forward to geting this exam out of the way. though im dreading the horrible amount of substance questions as i know this paper will be heavily focused on them due to tiny amount of it in the last paper. *starts a past paper*

Reply 46

sidra111

1

hi guys, i've done jan 2012 past paper for chem1. one question that i'm really struggling with is Q 6A and 3e.
can somoen explain it to me, that would be great! my math skills are not great :frown:

thanks

Reply 47

sechdent8

7

hey guys could someone please explain question 2 c) ii) in this paper please : http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM1-W-QP-JAN11.PDF
ive been trying it for ages but i cant seem to get it...

Reply 48

tony_dolby

10

Original post by sechdent8

hey guys could someone please explain question 2 c) ii) in this paper please : http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM1-W-QP-JAN11.PDF
ive been trying it for ages but i cant seem to get it...

It's a bit of a nightmare. First you'll need a bit of maths. Let's call the relative abundance of 113In 'x' and the relative abundance of 115In 'y'. The total abundance will therefore be simply 'x +y'. Now comes the clever bit. Let's call the total abundance 1 and turn our relative abundances into decimals. 113In will still be x, but 115In will now be 1-x. Doing this gets rid of the nasty y bit.

Now for some simple maths.

113x + 115 (1-x) = 114.5
113x + 115 -115x = 114.5
-2x = -0.5
x= 0.25

Therefore the ratio of 113: 115 is 0.25 : 0.75

Reply 49

tony_dolby

10

Original post by sidra111

hi guys, i've done jan 2012 past paper for chem1. one question that i'm really struggling with is Q 6A and 3e.
can somoen explain it to me, that would be great! my math skills are not great :frown:

thanks

First calculate the moles of Pb using Moles = Mass/Ar
Now calculate the moles of nitric acid by dividing by 3 and multiplying by 8
You now have the moles of nitric acid and you know the conc. (2.00 M). Finding the volume is now trivial.

Reply 50

sechdent8

7

Original post by tony_dolby

It's a bit of a nightmare. First you'll need a bit of maths. Let's call the relative abundance of 113In 'x' and the relative abundance of 115In 'y'. The total abundance will therefore be simply 'x +y'. Now comes the clever bit. Let's call the total abundance 1 and turn our relative abundances into decimals. 113In will still be x, but 115In will now be 1-x. Doing this gets rid of the nasty y bit.

Now for some simple maths.

113x + 115 (1-x) = 114.5
113x + 115 -115x = 114.5
-2x = -0.5
x= 0.25

Therefore the ratio of 113: 115 is 0.25 : 0.75

i get everything apart from the 1-x bit, how did you get that? please explain

Reply 51

tony_dolby

10

I got the 1-x by assuming the total abundance was 1. If x is the amount of one isotope, then the amount of the other must be the total amount (which I have called 1) minus the amount of x. As we only have 2 isotopes here, it makes life a lot easier.

I called have called the total abundance 100 and made percentages out of it - this makes no difference. In this case it would be (100-x) rather than 1-x . This assumption is what makes this question difficult.

I hope this makes sense.

Reply 52

MediterraneanX

16

So not looking forward to this paper - I seem to be ok with every topic except bonding shapes! Does anyone have any good online resources for this?

Reply 53

sechdent8

7

yep it makes perfect sense thank you so much! :biggrin:

Reply 54

mynamee

OP

10

Original post by MediterraneanX

So not looking forward to this paper - I seem to be ok with every topic except bonding shapes! Does anyone have any good online resources for this?

I found the CGP guide very helpful for the electron names!
Sorry I don't have a scanner, but I tried to take a photo and attach it

Hey

resitting this exam on Tuesday and need to get my UMS up if I want to get into university! Can anyone help me with the types of molecular bonds and how you know what they are? For example, in a paper it asks what type of bonds are in Hydrogen Sulfide. Are we just supposed to know this or is there a way of working it out? Similarly, predict the type of bonding in Sodium Sulfide. I don't understand how we are supposed to know, unless I've just completely missed out a page in the book somewhere where it tells me! Any help would be appreciated as this type of question is the one I usually fall down on!

Thanks :smile:

Reply 56

MediterraneanX

16

Original post by mynamee

I found the CGP guide very helpful for the electron names!
Sorry I don't have a scanner, but I tried to take a photo and attach it

Thank you thats very kind - just gone out and bough the CGP guide in a panic haha!

Reply 57

MediterraneanX

16

Original post by jodiedoodles

Hey

resitting this exam on Tuesday and need to get my UMS up if I want to get into university! Can anyone help me with the types of molecular bonds and how you know what they are? For example, in a paper it asks what type of bonds are in Hydrogen Sulfide. Are we just supposed to know this or is there a way of working it out? Similarly, predict the type of bonding in Sodium Sulfide. I don't understand how we are supposed to know, unless I've just completely missed out a page in the book somewhere where it tells me! Any help would be appreciated as this type of question is the one I usually fall down on!

Thanks :smile:

Look back in your book to the bonding chapter. Hydrogen bonds only form between hydrogen and nitrogen/oxygen/fluoride so for example if they ask what the strongest bonds in a H20 molecule are you'd say hydrogen bonds because theres a H and O (and hydrogen bonds are the strongest bonds). For anything else its like to be van der waals bonds as they're in pretty much everything. Depending on the wording of the question they might be asking you to identify whether its going to be ionic/covalent/metallic bonding. Just look up the elements on the periodic table and use the rules in the book to determine what they are (eg two metals will always be metallic bonding etc).

Reply 58

sidra111

1

Original post by tony_dolby

First calculate the moles of Pb using Moles = Mass/Ar
Now calculate the moles of nitric acid by dividing by 3 and multiplying by 8You now have the moles of nitric acid and you know the conc. (2.00 M). Finding the volume is now trivial.

why do you divide it by 3 and multiply by 8 :confused:

(edited 11 years ago)

Reply 59

tony_dolby

10

Original post by sidra111

why do you divide it by 3 and multiply by 8 :confused:

Because the ratio is 3 moles of Pb to 8 moles of nitric acid. We know the number of moles of Pb but we need to find the moles of nitric acid. Often this ratio is 1:2, but this time it's 3:8 !!! However, the principle is the same: we simply multiply the moles of Pb by 8/3 to find how many moles of nitric acid were used up.

AQA CHEM1: 15th May 2012

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