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QCE Chemistry Questions Thread
keltingmeith:
--- Quote from: laurahhh on September 22, 2020, 08:16:03 pm ---
Thank you! :)
I got halfway there so I guess I'm not too bad. But the answer from the textbook said the molarity of HCl was 0.5M. Which is why I'm very confused.
--- End quote ---
So, I independently went over my answer again, and realised I did make one mistake - the mole ratio of HCl and carbonate above is wrong, so it should be:
But that brings the final answer to 0.2 M (multiply my original answer by 4), not 0.5 M. I disagree with both, because the smallest amount of sig figs we're given is 3, not 1. But yeah, not sure how they get 0.5 M, likely a typo. I also looked up the question on-line and found a bunch of other people answering it, and they all agree with me. So, if you're not willing to trust some random on AN, how about some random on AN + 2 other randoms on the internet ;)
Bri MT:
--- Quote from: laurahhh on September 22, 2020, 08:16:03 pm ---
Thank you! :)
I got halfway there so I guess I'm not too bad. But the answer from the textbook said the molarity of HCl was 0.5M. Which is why I'm very confused.
--- End quote ---
--- Quote from: keltingmeith on September 22, 2020, 08:33:30 pm ---So, I independently went over my answer again, and realised I did make one mistake - the mole ratio of HCl and carbonate above is wrong, so it should be:
But that brings the final answer to 0.2 M (multiply my original answer by 4), not 0.5 M. I disagree with both, because the smallest amount of sig figs we're given is 3, not 1. But yeah, not sure how they get 0.5 M, likely a typo. I also looked up the question on-line and found a bunch of other people answering it, and they all agree with me. So, if you're not willing to trust some random on AN, how about some random on AN + 2 other randoms on the internet ;)
--- End quote ---
It's not rare for textbooks to have some mistakes in them.
Highschool doesn't really have the right terminology for it but I had keltingmeith as a "substitute teacher" in 1st year uni chemistry & as his signature says he's been doing a PhD in chemistry - I'd definitely recommend you trust this "random" over the textbook answer.
Declan.B:
Hi,
The QCE syllabus mentions using analytical techniques, including x-ray crystallography to determine the structure of organic molecules. I haven't done much of that in class and have had some difficulty finding questions relevant to this online. Also, the mock exam had no significant question relating to x-ray crystallography in this way.
I'm happy with my knowledge of how x-ray crystallography works, but I'm having trouble finding questions where it is used to predict the structures of organic molecules at a year 12 level.
keltingmeith:
--- Quote from: Declan.B on September 29, 2020, 12:09:18 pm ---Hi,
The QCE syllabus mentions using analytical techniques, including x-ray crystallography to determine the structure of organic molecules. I haven't done much of that in class and have had some difficulty finding questions relevant to this online. Also, the mock exam had no significant question relating to x-ray crystallography in this way.
I'm happy with my knowledge of how x-ray crystallography works, but I'm having trouble finding questions where it is used to predict the structures of organic molecules at a year 12 level.
--- End quote ---
So, I've done x-ray crystallography before. It's hard. And not just the doing it bit, but the actual trying to use it to find a structure bit. We're talking about requiring to do millions of calculations for a 10 atom asymmetric unit. You won't be expected to predict a structure based on x-ray data - it's just not feasible. I think it's safe to assume you should only need to be able to identify XRD as a potential tool, or maybe to discuss how it works. I think the fact that it's not directly in the sample exams is quite telling of what you can expect from it.
Declan.B:
--- Quote from: keltingmeith on September 29, 2020, 01:00:43 pm ---So, I've done x-ray crystallography before. It's hard. And not just the doing it bit, but the actual trying to use it to find a structure bit. We're talking about requiring to do millions of calculations for a 10 atom asymmetric unit. You won't be expected to predict a structure based on x-ray data - it's just not feasible. I think it's safe to assume you should only need to be able to identify XRD as a potential tool, or maybe to discuss how it works. I think the fact that it's not directly in the sample exams is quite telling of what you can expect from it.
--- End quote ---
Alright, thank you.
It did seem very complex from what I saw online, as is why I was wondering the year 12 applicable parts. Yet, this is what the syllabus stated on it:
"select and use data from analytical techniques, including mass spectrometry,
x-ray crystallography and infrared spectroscopy, to determine the structure of
organic molecules".
Does this seem to be an error on the QCAA's part with the x-ray crystallography component?
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