AQA Chemistry C3 UNOFFICIAL MARK SCHEME

Reply 40

Kirby711

5

Original post by AishaTara

YAY

They didn't have all of them there, just to add. If I was the examiner I'd give the mark...

Reply 41

nadster

12

Question 10 I reckon had something to do with the sample size.

Reply 42

AishaTara

14

Original post by Kirby711

They didn't have all of them there, just to add. If I was the examiner I'd give the mark...

well you would then be in the top 10 examiner list for 2011

Reply 43

nadster

12

Original post by mohsi

'10. Why would instrumental analysis be better than chemical analysis? Because instrumental analysis is much more accurate and can detect very little amounts, whereas chemical analysis cannot. (1 mark)'

I thought the question was actually saying why does intrumental analysis have to be used for Iron in particular, rather than a chemical test, and I wrote that Iron is a transition metal so it is not reactive and the chemical test would have no effect identifying it (or whatever it was they had to do), whereas the instrumental analysis would be able to. Is that wrong?

That wasn't how the question was phrased. It was something like: why would instrumental analysis work and not chemical analysis. It stated in the question that the sample size was small and we got taught that you can only use a small sample size for instrumental analysis - chemical analysis requires a larger sample size

Reply 44

Conan

1

Original post by mohsi

'10. Why would instrumental analysis be better than chemical analysis? Because instrumental analysis is much more accurate and can detect very little amounts, whereas chemical analysis cannot. (1 mark)'

I thought the question was actually saying why does intrumental analysis have to be used for Iron in particular, rather than a chemical test, and I wrote that Iron is a transition metal so it is not reactive and the chemical test would have no effect identifying it (or whatever it was they had to do), whereas the instrumental analysis would be able to. Is that wrong?

I think that they wanted you to write something along the lines of instrumental analysis is far more sensitive and accurate

Reply 45

nadster

12

And I'm not 100% sure about your answer...may be right...not sure

Reply 46

scaryassmonster

i know this has been asked many times already, but for question 26, wouldn't the answer be 0.128x34? because its 2NH3, so you multiply the Ar by 2 to find the Mr of ammonia?

Reply 47

nadster

12

Original post by scaryassmonster

i know this has been asked many times already, but for question 26, wouldn't the answer be 0.128x34? because its 2NH3, so you multiply the Ar by 2 to find the Mr of ammonia?

No, because you have included the 2 moles in your previous answer. By multiplying it by two again, you are saying that there are 4 moles

Reply 48

AishaTara

14

Original post by scaryassmonster

i know this has been asked many times already, but for question 26, wouldn't the answer be 0.128x34? because its 2NH3, so you multiply the Ar by 2 to find the Mr of ammonia?

Nope because that would be per two moles, and you have to give the answer per mole ( the units were already given to us, and also the standard unit used is per mole dm cubed)

Reply 49

Conan

1

Original post by nadster

That wasn't how the question was phrased. It was something like: why would instrumental analysis work and not chemical analysis. It stated in the question that the sample size was small and we got taught that you can only use a small sample size for instrumental analysis - chemical analysis requires a larger sample size

I don't think the sample size was small. It was the amount of iron impurities that was in there which was small. :smile:

The bit in bold is true but I'm not sure whether it's relevent :s-smilie:

So you really had to mention the fact that instrumental analysis would be more sensitive

(edited 12 years ago)

Reply 50

AishaTara

14

Original post by mohsi

'10. Why would instrumental analysis be better than chemical analysis? Because instrumental analysis is much more accurate and can detect very little amounts, whereas chemical analysis cannot. (1 mark)'

I thought the question was actually saying why does intrumental analysis have to be used for Iron in particular, rather than a chemical test, and I wrote that Iron is a transition metal so it is not reactive and the chemical test would have no effect identifying it (or whatever it was they had to do), whereas the instrumental analysis would be able to. Is that wrong?

Hm, that could possibly be one of the answers. sometimes they offer three or four answers so who knows you may well be right!

Reply 51

nadster

12

Original post by Conan

I don't think the sample size was small. It was the amount of iron impurities that was in there which was small. :smile:

The bit in bold is true but I'm not sure whether it's relevent :s-smilie:

So you really had to mention the fact that instrumental analysis would be more sensitive

No, I'm certain that it said the sample size was small.

Reply 52

WelshDragon23

10

Original post by tallguitarist

i put group 8 instead of group 0, would i get a mark?

Absolutely, both are correct. Personally, I put Group 0, the noble gases (just to clarify it to them :P) but Group 8 is a correct definition also :biggrin:

. And to the guy that made this unofficial mark scheme, thanks a lot. I know it takes a lot of work, I did one ages ago.

Reply 53

AspiringGenius

15

I need 85 UMS to get A* :frown:

I thought the test was really hard and everybody found it easy. :frown:

and what's worse, I want to do medicine so I'm pretty stuffed now...

Reply 54

Kirby711

5

Just to ask, did question 2 mention Washing soda/sodium carbonate? It's misleading with the soap mentioned...

Reply 55

Conan

1

Original post by nadster

No, I'm certain that it said the sample size was small.

Oh dear, I'm sure it's the amount of iron that was in the sameple that was small... :s-smilie:

Reply 56

britash

2

I've lost a mark on the very first question. I found it rather confusing. Just said that the magnesium and chlorine numbers (listed them) were 4 times and 2.5 times bigger on the other water, and 3 was the average between the two. I didn't say another about 100g and 30g or something like other people have mentioned :frown:

I also messed up on the 'Why is it worrying if they say it doesn't contain chemicals?' - Completely forgot about bacteria. Wrote a load of rubbish about elements O.o
Transition element I wrote about it won't corrode or rust easily and it has a very high melting point.
I got the 0.685 (or something) for the concentration, but accidently doubled the correct answer in part (iii) because I saw there were two moles :frown:

Oh well. I *should* have about 36/45. I only needed 10/45 for an A and about 32/45 for an A*
Fingers crossed I've got it :P x

Reply 57

nadster

12

Original post by Conan

Oh dear, I'm sure it's the amount of iron that was in the sameple that was small... :s-smilie:

Well, I may be wrong then...

Reply 58

destinyx

Original post by nadster

That wasn't how the question was phrased. It was something like: why would instrumental analysis work and not chemical analysis. It stated in the question that the sample size was small and we got taught that you can only use a small sample size for instrumental analysis - chemical analysis requires a larger sample size

Oh yeah I remember that question. I remember it saying something along the lines off there was a very small bit on Iron in the substance? So why was it better to use instrumental analysis rather than chemical. I thought it was because chemical analysis may not be accurate enough to pick up this small sample of Iron or something a long those lines.