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Chemistry Exam Predictions/Thoughts (3 Viewers)

luminol

luminol

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It's interesting how the HSC exam specifications state that at least two sub-questions in chem will be worth 7-9 marks although a lot of the school trial papers don't include huge questions/split them into bite-sized pieces. Maybe not so common in chem since an integrated spectra question can easily fill part of the quota, but still quite a handful.
 
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james049

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🍑 this is a peach said:
there were sooo many mistakes 😂... do they even bother proof reading it?
and there were mistakes in other cssa papers too, in software there was a question not even relevant to the syllabus
Click to expand...
question 23 has a mistakes as well, the question says there's a peak at 88.1, but no peak can be seen for both spectrums
 
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roryg03

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luminol said:
It's interesting how the HSC exam specifications state that at least two sub-questions in chem will be worth 7-9 marks although a lot of the school trial papers don't include huge questions/split them into bite-sized pieces. Maybe not so common in chem since an integrated spectra question can easily fill part of the quota, but still quite a handful.
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yeah was thinking about this, reckon they would ask to explain how one of the spec techniques works?
 
C

CM_Tutor

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james049 said:
question 23 has a mistakes as well, the question says there's a peak at 88.1, but no peak can be seen for both spectrums
Click to expand...
The peaks are small, but they are present... here is an enlarged picture of the MS:

2021 CSSA q23.png

Note that posting this image is not a copyright violation as CSSA does not hold the copyright on these... the images come from the Spectral Database for Organic Compounds, as the paper acknowledged.
 
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cassicowfan

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CM_Tutor said:
Regarding the CSSA 2021 paper, it should be noted that there were a lot of mistakes:
  • In question 2, none of the equations are correct. The answer is meant to be D but there is a typo in the formula for aluminium carbonate. It should be Al2(CO3)3 but has been incorrectly written as Al2(CO2)3.
  • Question 20 has no correct answer, which is 0.0124 mol L-1. The answer given, C, is 0.00502 mol L-1 is the concentration of lead ions in the solution when the precipitate first forms, but the question asked for the concentration in the aliquot.
  • Not a mistake, but question 26(b) can be done with a variety of methods.
  • Few people will notice, but the graph in question 27 is wrong. If you use the periods when the system is at equilibrium to estimate the equilibrium constant, you will find that it is roughly K = 0.097 to start with, decreases to K = 0.046 after the temperature change (which is fine), but then after the volume change it decreases again to K = 0.015. The movements in concentration following the volume change are in the right direction but they should be changes of roughly 0.25 mol L-1.
  • Question 33 begins by stating that isomers have formula C4H8O. There are quite a few possible alcohols with this MF, but I can't think of any that has a 1H NMR spectrum like the one shown. Further, the question gives the relative areas for the five hydrogen environments as 3:3:2:1:1, which means the compound has 10 hydrogen atoms! There are only four possible alcohols with MF of C4H10O, one of which (2-butanol) matches the given NMR spectrum. I conclude that the question starts with the wrong formula and I wonder how many students were confused by this mistake and lost time.
  • Question 34 asserts that "... whereas amphiprotic sodium hydrogen carbonate forms a solution with a pH of 1." This is preposterous, ridiculous, absurd, wrong, and total and complete bovine waste product. Sodium hydrogencarbonate is amphiprotic but is actually a weak base. If it truly had a pH of 1, its conjugate acid (carbonic acid, which is weak, pKa = 6.8) would need to have a pH that was negative. Looking at the solutions, I have found that the question is meant to say that "sodium hydrogen sulfate forms a solution with a pH of 1." This is at least an acidic substance, and it is formally amphiprotic in that it has a conjugate acid and a conjugate base. However, having hydrogensulfate accept a proton and form sulfuric acid (which is strong, with a pKa of -2.8) would require unusual circumstances. The hydrogensulfate ion has a pKa of 2 and so would need to be present in a concentration of 1.0 mol L-1 to have a pH of 1.
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What are some of the other methods for q26)b?, I can only think of the method they put in their answers
 
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JesusChriiii

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Good night everyone and good luck for tomorrow! Get some good sleep tonight ! For many people it will be their last exam, all the effort will pay off eventually!
 
🍑 this is a peach

🍑 this is a peach

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- SIX calculations in multiple choice
- g l u c o s e
- g i b b s f r e e e n e r g y
- 2 7 markers
- ?? wtf titration
- ???? HOW keq/ksp last question???
 
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