AQA A-Level Chemistry (7405) Exam Thread - June 13th, June 19th and June 27th
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Original post by ssh555
E: https://pubchem.ncbi.nlm.nih.gov/compound/aniline
F: https://pubchem.ncbi.nlm.nih.gov/compound/1001
G: https://pubchem.ncbi.nlm.nih.gov/compound/7670
Then go down to around section 4.2 for pKa. The point I was trying to make in my first post was E < G < F or F > G > E, the order doesn't matter it's the fact that E is a weaker base than G.
Posted from TSR Mobile
F: https://pubchem.ncbi.nlm.nih.gov/compound/1001
G: https://pubchem.ncbi.nlm.nih.gov/compound/7670
Then go down to around section 4.2 for pKa. The point I was trying to make in my first post was E < G < F or F > G > E, the order doesn't matter it's the fact that E is a weaker base than G.
Posted from TSR Mobile
I was halfway through a reply haha, thanks. This was a good point to make
Ctrl+F for pKa is probably a bit quicker
(edited 6 years ago)
Original post by ssh555
E: https://pubchem.ncbi.nlm.nih.gov/compound/aniline
F: https://pubchem.ncbi.nlm.nih.gov/compound/1001
G: https://pubchem.ncbi.nlm.nih.gov/compound/7670
Then go down to sections: 4.2.23 for E, 4.2.11 for F, 4.2.19 for G. The point I was trying to make in my first post was E < G < F or F > G > E, the order doesn't matter it's the fact that E is a weaker base than G.
Posted from TSR Mobile
F: https://pubchem.ncbi.nlm.nih.gov/compound/1001
G: https://pubchem.ncbi.nlm.nih.gov/compound/7670
Then go down to sections: 4.2.23 for E, 4.2.11 for F, 4.2.19 for G. The point I was trying to make in my first post was E < G < F or F > G > E, the order doesn't matter it's the fact that E is a weaker base than G.
Posted from TSR Mobile
Hi, thanks for that. Really was helpful as I couldn't find the 3 molecules myself online. According to online sources, the Higher the pKa the stronger the base meaning that E is the weakest, G is in the middle and F is a much stronger base. So this contradicts what others were saying about it PID making the electrons delocalised.
Original post by apixytm
The ethyl group DID push the e- into benzene more. When Nitrogen is directly bonded to benzene their e- are partially delocalised into benzene but the presence of the ethyl group pushed the e- further hence reducing the availability of lone pair even more. This was the weakest base, not the one with amine group only as I've heard people say (their reasons being that the ethyl group cancels the effect of lost electrons into benzene by making it more positive, that's not true for how a Lewis base works).
Check out the pKa values - this shows that the G is a stronger base than E (the one with the amine group)
Feels like there is not a lot you can do for this paper asides from reading over assessed practicals and just going over content from entire specification.
Asides from calorimetry, purifying organic compounds and esters (Only ones I can really think of as topics that haven''t been touched) anyone else got any other ideas?
Asides from calorimetry, purifying organic compounds and esters (Only ones I can really think of as topics that haven''t been touched) anyone else got any other ideas?
Original post by danley
I don't think that "increasing" or "decreasing" is the point he's trying to make, he's arguing that E was the weakest base because it had the lowest pKa value- I agree with that. So it should be F > G > E.
How do you explain the pKa values for the three compounds then?
How do you explain the pKa values for the three compounds then?
Original post by ssh555
E: https://pubchem.ncbi.nlm.nih.gov/compound/aniline
F: https://pubchem.ncbi.nlm.nih.gov/compound/1001
G: https://pubchem.ncbi.nlm.nih.gov/compound/7670
Then go down to sections: 4.2.23 for E, 4.2.11 for F, 4.2.19 for G. The point I was trying to make in my first post was E < G < F or F > G > E, the order doesn't matter it's the fact that E is a weaker base than G.
Posted from TSR Mobile
F: https://pubchem.ncbi.nlm.nih.gov/compound/1001
G: https://pubchem.ncbi.nlm.nih.gov/compound/7670
Then go down to sections: 4.2.23 for E, 4.2.11 for F, 4.2.19 for G. The point I was trying to make in my first post was E < G < F or F > G > E, the order doesn't matter it's the fact that E is a weaker base than G.
Posted from TSR Mobile
Yes I agree to what you have argued but pKa is dependent on the stability of the conjugate acid. Can it be used to tell us the true basic strength? To a point yes.
Revisit the pages you have provided, then CTRL+F for solubility. You will find that solubility increases in the order - G,E,F
Then CTRL+F for pH, again it increases in this order G,E,F. pH doesn't necessarily show strength but if the values stated are at a standard concentration then E is stronger base than G.
What can make E more soluble than G is the availability of the lone pair on N.
It is the same case as why strength of NH3< primary amine ~ tertiary amine < secondary amine as a base is.
The main reason tertiary amine is less basic than secondary is because it is less soluble in a solution.
The letters are in reference to what you assigned, I do remember writing different letters in the exam.
Spoiler
(edited 6 years ago)
Original post by ssh555
E: https://pubchem.ncbi.nlm.nih.gov/compound/aniline
F: https://pubchem.ncbi.nlm.nih.gov/compound/1001
G: https://pubchem.ncbi.nlm.nih.gov/compound/7670
Then go down to sections: 4.2.23 for E, 4.2.11 for F, 4.2.19 for G. The point I was trying to make in my first post was E < G < F or F > G > E, the order doesn't matter it's the fact that E is a weaker base than G.
Posted from TSR Mobile
F: https://pubchem.ncbi.nlm.nih.gov/compound/1001
G: https://pubchem.ncbi.nlm.nih.gov/compound/7670
Then go down to sections: 4.2.23 for E, 4.2.11 for F, 4.2.19 for G. The point I was trying to make in my first post was E < G < F or F > G > E, the order doesn't matter it's the fact that E is a weaker base than G.
Posted from TSR Mobile
Yes this is correct, went through it with my teacher yesterday and she agreed that it went E<G<F
Original post by Gogregg
I was just discussing this with my chemistry teacher, and we haven't really managed to come to any conclusion.
The previous papers have been quite fair and have covered pretty much everything on the specification. So really anything could come up!
In terms of practicals, calorimetry could come up, as they haven't asked any graph skills, but then again it could be the standard solution and titration question, as that lends itself to calculations.
There may be questions on transition metals and NMR, and we're assuming there'll be a few practical skills and calculations in the multiple choice questions
It's hard to call really
Also, my chemistry teacher thinks that an A will be somewhere around 200-210, so take from that as you will
The previous papers have been quite fair and have covered pretty much everything on the specification. So really anything could come up!
In terms of practicals, calorimetry could come up, as they haven't asked any graph skills, but then again it could be the standard solution and titration question, as that lends itself to calculations.
There may be questions on transition metals and NMR, and we're assuming there'll be a few practical skills and calculations in the multiple choice questions
It's hard to call really
Also, my chemistry teacher thinks that an A will be somewhere around 200-210, so take from that as you will
Just wondering, AS was 64% for an A last year so why would it be higher for A2 - the first year of the linear course ygm
I know it's just what your teacher said but I'm praying for low grade boundaries hahah and just wondered if it would be similar or lower to AS which many people think idk
has anyone got the set 2 paper for paper 3 and the mark scheme?
Original post by sarahplatts
Just wondering, AS was 64% for an A last year so why would it be higher for A2 - the first year of the linear course ygm
I know it's just what your teacher said but I'm praying for low grade boundaries hahah and just wondered if it would be similar or lower to AS which many people think idk
I know it's just what your teacher said but I'm praying for low grade boundaries hahah and just wondered if it would be similar or lower to AS which many people think idk
I understand completely, but the papers this year, so far, have been a lot nicer and much more fair then the AS papers. While it's pretty much the same people taking them, you also have the introduction of people who didn't do the AS, but also some people who dropped or failed chemistry last year. That's sort of the basis for believing there will be an increase.
Also, 70% is still quite low, right? A lot of prior find chemistry very difficult, so the grade boundaries are never going to be super high, but we think they may be higher this year.
That said, it is all speculation
Hey everyone,
Hope revision is going well.
Just wanted to clear something up in terms of grading; am I right in saying that as grades are determined by the percentage achieved as a total of all three papers, it doesn't actually matter which paper you got the marks from?
I mean to say, could I get 80 marks on paper 1, 80 on paper 2 and 60 on paper 3 and still get an A? (Not those exact marks, obviously, but just as an example.)
Hope revision is going well.
Just wanted to clear something up in terms of grading; am I right in saying that as grades are determined by the percentage achieved as a total of all three papers, it doesn't actually matter which paper you got the marks from?
I mean to say, could I get 80 marks on paper 1, 80 on paper 2 and 60 on paper 3 and still get an A? (Not those exact marks, obviously, but just as an example.)
Original post by apixytm
Yes I agree to what you have argued but pKa is dependent on the stability of the conjugate acid. Can it be used to tell us the true basic strength? To a point yes.
Revisit the pages you have provided, then CTRL+F for solubility. You will find that solubility increases in the order - G,E,F
Then CTRL+F for pH, again it increases in this order G,E,F. pH doesn't necessarily show strength but if the values stated are at a standard concentration then E is stronger base than G.
What can make E more soluble than G is the availability of the lone pair on N.
It is the same case as why strength of NH3< primary amine ~ tertiary amine < secondary amine as a base is.
The main reason tertiary amine is less basic than secondary is because it is less soluble in a solution.
The letters are in reference to what you assigned, I do remember writing different letters in the exam.
Revisit the pages you have provided, then CTRL+F for solubility. You will find that solubility increases in the order - G,E,F
Then CTRL+F for pH, again it increases in this order G,E,F. pH doesn't necessarily show strength but if the values stated are at a standard concentration then E is stronger base than G.
What can make E more soluble than G is the availability of the lone pair on N.
It is the same case as why strength of NH3< primary amine ~ tertiary amine < secondary amine as a base is.
The main reason tertiary amine is less basic than secondary is because it is less soluble in a solution.
The letters are in reference to what you assigned, I do remember writing different letters in the exam.
Spoiler
My teacher also seems to agree that E is the weakest base. The pH value for compound G seems like an error, it shouldn't be acidic surely.
Your explanation is fairly convincing though, but seems much too advanced for the A-level- judging from the spec and the information that we are required to know about bases, ours is surely the logical conclusion that they would want students to reach?
If you're right, then they have probably structured the question to still allow 4-5 marks for answers that reversed G and E perhaps?
(edited 6 years ago)
Original post by danley
My teacher also seems to agree that E is the weakest base. The pH value for compound G seems like an error, it shouldn't be acidic surely.
Your explanation is fairly convincing though, but seems much too advanced for the A-level- judging from the spec and the information that we are required to know about bases, ours is surely the logical conclusion that they would want students to reach?
If you're right, then they have probably structured the question to still allow 4-5 marks that reversed G and E perhaps?
Your explanation is fairly convincing though, but seems much too advanced for the A-level- judging from the spec and the information that we are required to know about bases, ours is surely the logical conclusion that they would want students to reach?
If you're right, then they have probably structured the question to still allow 4-5 marks that reversed G and E perhaps?
I would also say the order was max 2marks. No more than that, as the key part of the question was to explain the different bases. Availability of lone pair on N, alkyl groups electron releasing (positive induction), lone pair on N delocalised into benzene are some marking points along with others that potentially could be mentioned, most for each base as well. I may be wrong who knows.
Original post by apixytm
I would also say the order was max 2marks. No more than that, as the key part of the question was to explain the different bases. Availability of lone pair on N, alkyl groups electron releasing (positive induction), lone pair on N delocalised into benzene are some marking points along with others that potentially could be mentioned, most for each base as well. I may be wrong who knows.
Definitely, hard to see how they would fit the other points in otherwise.
Original post by PBC Gyal
All I wish for paper 3 is for questions asking about content to come up! Pure content what we do know and should be tested on! 😩
Yoo what does PBC mean lool
what do you guys think will come up in paper three
Original post by lisaaasarahh
what do you guys think will come up in paper three
Graph of some sort has to come up. Maybe arrhenius or a gibbs free energy graph, trends? Who knows...
Original post by apixytm
Yes I agree to what you have argued but pKa is dependent on the stability of the conjugate acid. Can it be used to tell us the true basic strength? To a point yes.
Revisit the pages you have provided, then CTRL+F for solubility. You will find that solubility increases in the order - G,E,F
Then CTRL+F for pH, again it increases in this order G,E,F. pH doesn't necessarily show strength but if the values stated are at a standard concentration then E is stronger base than G.
What can make E more soluble than G is the availability of the lone pair on N.
It is the same case as why strength of NH3< primary amine ~ tertiary amine < secondary amine as a base is.
The main reason tertiary amine is less basic than secondary is because it is less soluble in a solution.
The letters are in reference to what you assigned, I do remember writing different letters in the exam.
Revisit the pages you have provided, then CTRL+F for solubility. You will find that solubility increases in the order - G,E,F
Then CTRL+F for pH, again it increases in this order G,E,F. pH doesn't necessarily show strength but if the values stated are at a standard concentration then E is stronger base than G.
What can make E more soluble than G is the availability of the lone pair on N.
It is the same case as why strength of NH3< primary amine ~ tertiary amine < secondary amine as a base is.
The main reason tertiary amine is less basic than secondary is because it is less soluble in a solution.
The letters are in reference to what you assigned, I do remember writing different letters in the exam.
Spoiler
Hi, I completely see what your getting at but surely, even if teachers are saying it too it must be E<G<F.
Original post by chembiodood
Graph of some sort has to come up. Maybe arrhenius or a gibbs free energy graph, trends? Who knows...
Arrhenius already appeared in paper 2 though
Original post by PBC Gyal
All I wish for paper 3 is for questions asking about content to come up! Pure content what we do know and should be tested on! 😩
Ugh same!!!! I did so many silly mistakes on paper 1 and 2. And I was really p***** that AS organic theory didn't come up
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