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(https://i.imgur.com/oa1YfQV.png)
This thread is for all exam-related discussion. Was it easy? Was it hard? What did you get for each question? Feel free to post any and all of your thoughts below.
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VCAA 2018 Chemistry Exam Provisional Solutions
Solutions by Kevin Mao at TWM Publications
Full worked solutions available for Section B only. Section A has answers but no working or justification. We'll get to Section A some day, but most of you would've forgot this exam by then lol. Enjoy!
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Which one has the lower GI?
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Which one has the lower GI?
The whole coconut, right?
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The whole coconut, right?
yes! due to lower rate of reaction
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From the people I asked, the general consensus was that it was easy, however it was quite long. Idk what's up with the mostly easy exams this year for math/science.
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From the people I asked, the general consensus was that it was easy. Idk what's up with the mostly easy exams this year for math/science.
yeah it was easier then expected. wats the a plus cut off?
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What did ya'll get for the calibration factor?
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What did ya'll get for the calibration factor?
680 or something
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As I expected, the exam was extremely long just like the 2018 NHT. Although I’d say the content was much easier. Perhaps even easier than last year’s.
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680 or something
yeah same
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680 or something
How many significant figures did you give it to? Since the mass of KNO3 was given to 1 sig fig I think?
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How many significant figures did you give it to? Since the mass of KNO3 was given to 1 sig fig I think?
2 sig figs.
the mass was given in 2 sig figs i think 3.0g
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2 sig figs.
the mass was given in 2 sig figs i think 3.0g
pretty sure it was just 3 grams
all i wanna say is thank u vcaa for not putting 13 marks of horrendous experimental design questions like last year :-X
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pretty sure it was just 3 grams
all i wanna say is thank u vcaa for not putting 13 marks of horrendous experimental design questions like last year :-X
Yeah, I could've sworn it said 3g.
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I remember it as 3.0g as well, is it true that you get only one mark deducted across the whole exam for incorrect sig figs?
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I remember it as 3.0g as well, is it true that you get only one mark deducted across the whole exam for incorrect sig figs?
yes
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You can only lose 1 mark across the exam for significant figures.
Also, in the materials table, it says "3 g of potassium nitrate (\(\text{KNO}_3\))", but in the Methods section for the calibration, it says "Measure 3.0 g of \(\text{KNO}_3\) accurately", so I suspect, you're meant to use 3.0 g
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You can only lose 1 mark across the exam for significant figures.
Also, in the materials table, it says "3 g of potassium nitrate (\(\text{KNO}_3\))", but in the Methods section for the calibration, it says "Measure 3.0 g of \(\text{KNO}_3\) accurately", so I suspect, you're meant to use 3.0 g
thats an error on their behalf. having two masses with differing sig figs
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What did u guys get for the concentration of ethanol in cellulose or something along the lines of that (in % m/m)
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thats an error on their behalf. having two masses with differing sig figs
Yeah, what's up with that crap? Such a stupid thing to do...
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What did u guys get for the concentration of ethanol in cellulose or something along the lines of that (in % m/m)
11.375% =11%
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Did you take into account that only a certain percentage of the plant is cellulose?
Well I forgot to and I got 30 something percent, the percentage of the plant was 37% so his 11% answer must be correct.
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Well I forgot to and I got 30 something percent, the percentage of the plant was 37% so his 11% answer must be correct.
im 100% sure i didnt forget to multiply by .37 and got 30 something percent. So hmmmmm.
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im 100% sure i didnt forget to multiply by .37 and got 30 something percent. So hmmmmm.
Haha same. Now I'm confused....
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I got around 30% as well
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Haha same. Now I'm confused....
Only 37% of plant m was cellulose, but the question stated that 1000kg of plant m produced 144L of ethanol. The percentage is irrelevant in this case as 144L was produced
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Only 37% of plant m was cellulose, but the question stated that 1000kg of plant m produced 144L of ethanol. The percentage is irrelevant in this case as 144L was produced
But it asked for the percentage by mass of cellulose, right?
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But it asked for the percentage by mass of cellulose, right?
No if it was percentage by mass of celloluse it would by 37% which is already given in the question
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what did you get for a systematic error
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what did you get for a systematic error
I think I wrote that the voltage in reality is not constant 6V. It fluctuates.
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same. I mentioned the voltmeter itself
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what about the skeletal formula for the amine?
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what did you get for a systematic error
I said the voltage and current was lower than estimated. Weird wording i know. But i was rushed. Do you think i'll still get a mark?
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I said the voltage and current was lower than estimated. Weird wording i know. But i was rushed. Do you think i'll still get a mark?
I reckon so
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what did you get for a systematic error
i said the wires' resistance could have reduced the current hence actually producing less heat energy.
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what about the skeletal formula for the amine?
I think it was sort of a triangle with an alkyl (ch2) and nh2 group attached on the top.
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No if it was percentage by mass of celloluse it would by 37% which is already given in the question
No I'm pretty sure it was by mass of cellulose... hopefully...
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Well, that went. :-\
I'm mad that I took so long and I didn't end up answering 10 marks or something, as I might've overthought the questions. I also spent too long on the amine question because I couldn't find the type of carbon and the other structural isomer until after 10 minutes. I do so awfully in the actual exam but when I do a practice I finish early what's going on
But really I'd rather not answer questions I will most likely get wrong than not answer questions I will most likely get right. I don't even know if my answer on Q1 and Q5 for multiple-choice is right. I don't remember my answer to the cellulose question was it like 113or114/370 x 100 or something
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I do so awfully in the actual exam but when I do a practice I finish early what's going on
This is normal. This exam, while very accessible in terms of difficulty, was super long. Found it same length as 2018 NHT exam. Writing speeds will contribute a lot to the separation between A+ and A cut
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No I'm pretty sure it was by mass of cellulose... hopefully...
But they literally gave the percentage by mass of cellulose in the question. It was percentage by mass of the ethanol derived from the cellulose
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This is normal. This exam, while very accessible in terms of difficulty, was super long. Found it same length as 2018 NHT exam. Writing speeds will contribute a lot to the separation between A+ and A cut
Hi Lear! :)
I was wondering what your opinion is on what the A+ cut would be this year?
Thanks in advance
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For the limitations, i wrote that the student didnt rinse the calorimeter and replace the water as some water in the electrical part may have evaporated. would i be correct? and for % of cellulose i got around 31%
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But they literally gave the percentage by mass of cellulose in the question. It was percentage by mass of the ethanol derived from the cellulose
Yeah, so dividing by 370kg should yield ~30%?
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For the limitations, i wrote that the student didnt rinse the calorimeter and replace the water as some water in the electrical part may have evaporated. would i be correct? and for % of cellulose i got around 31%
im pretty sure it was asking for the limitations of the chemical experiment conducted by student C. In that case would it not be the incomplete reaction of knh3 due to equilibrium?
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No if it was percentage by mass of celloluse it would by 37% which is already given in the question
From memory, 144L at a density of 0.87 = 128 kg or so;
Source cellulose was 37% of 1000kg = 370 kg;
Percentage by mass = 128/370 = 34 or so percent..
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Re the systematic error question, I thought that the transformation of electrical --> heat energy might not be 100% efficient, which would be a systematic error in that calibration system.
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im pretty sure it was asking for the limitations of the chemical experiment conducted by student C. In that case would it not be the incomplete reaction of knh3 due to equilibrium?
i thought it was asking for the limitations of the chemical calibration?
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From memory, 144L at a density of 0.87 = 128 kg or so;
Source cellulose was 37% of 1000kg = 370 kg;
Percentage by mass = 128/370 = 34 or so percent..
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Re the systematic error question, I thought that the transformation of electrical --> heat energy might not be 100% efficient, which would be a systematic error in that calibration system.
density was 0.79gml
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From memory, 144L at a density of 0.87 = 128 kg or so;
Source cellulose was 37% of 1000kg = 370 kg;
Percentage by mass = 128/370 = 34 or so percent..
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Re the systematic error question, I thought that the transformation of electrical --> heat energy might not be 100% efficient, which would be a systematic error in that calibration system.
Electric heaters are basically 100% efficient. Or are at least close to the point where we can consider them to be so.
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im pretty sure it was asking for the limitations of the chemical experiment conducted by student C. In that case would it not be the incomplete reaction of knh3 due to equilibrium?
Yeah i kinda goofed on this one (or i think)
I wrote that the students didn't allow the calorimetry to cool before using the KNO3.
My reasoning was that in the method it said "after electrical configuration....". and at the last step of the electrical method it stated "allow to cool for 3 minutes" which wasn't necessarily enough time to cool back to room temperature.
My limitation for the electrical one was something like "students only measured final voltage and not initial voltage, which may have been inconsistent"
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Honestly, i'm just glad there was no H-NMR on this exam.
The practice one i did before this had a peak at like 2.5 or something close to it which was meant to be R-CH2-R despite the data book saying the range was close to 1.3-1.4. (the book does say "these aren't always the correct values" but still a 1.0 difference is too much to expect)
i was also surprised by the lack of thermo-chemical equations and Delta H stuff
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Does anyone remember what they got for the IR and CNMR? Also what did the final molecule look like?
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For the systematic error for the electrical calibration, I said that the voltmeter may not give the exact voltage due to the possibility of it being faulty. Do you guys think that's a valid point?
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Does anyone remember what they got for the IR and CNMR? Also what did the final molecule look like?
I got 2 methyl propan-2-amine.
It looks like:
carbon centre, 3 methyls branching off with another amine branching off to make a
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Which one has the lower GI?
Idk if this is right but
I said smaller ones because the surface area of the smaller, thinner coconut shreds are greater, they can be packed together tightly and forms stronger forces in the body therefore, they are hydrolysed at a slower rate due to greater surface area hence lower GI.
The large coconut shreds have lower surface area and can’t be packed together tightly therefore forming weaker bonds and hence hydrolysed at a more rapid rate releasing more glucose in the blood levels hence higher GI for the large molecules
is this correct?! Maybe VCAA isn’t looking for a right answer but a justification of an answer.
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I thought it was 2-methyl propan-1-amine as there were 3 carbon environments present, 2-methylpropan-2-amine only has 2. Looks like this
Does anyone remember what they got for the IR and CNMR? Also what did the final molecule look like?
I got 2 methyl propan-2-amine.
It looks like:
carbon centre, 3 methyls branching off with another amine branching off to make a
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From memory, 144L at a density of 0.87 = 128 kg or so;
Source cellulose was 37% of 1000kg = 370 kg;
Percentage by mass = 128/370 = 34 or so percent..
...........
Re the systematic error question, I thought that the transformation of electrical --> heat energy might not be 100% efficient, which would be a systematic error in that calibration system.
Density was grams per mL
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is this correct?! Maybe VCAA isn’t looking for a right answer but a justification of an answer.
I don’t think so. A greater surface area increases the frequency of collisions and by extension the rate of traction. This is one of the reasons we chew foods before swallowing.
This was quite a good question considering textbook’s predominantly focus on the levels of amylopectin and amylose on GI, rather than the actual physical properties of the food. To answer this question students actually needed to bring together content learnt from unit 3 about rates of reaction and surface area with content from unit 4 on GI.
For next year students reading this, make sure you try and build connections between information you learnt throughout the year and not consider them completely separate.
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I thought it was 2-methyl propan-1-amine as there were 3 carbon environments present, 2-methylpropan-2-amine only has 2. Looks like this
Yeah, I got the same thing. Because of the symmetrical end, that reduced the number of carbon environments to match the graph
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Yeah, so dividing by 370kg should yield ~30%?
I didn't do that :'( :'( :'(
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How did you guys draw the skeletal structure for the molecule in NMR question?
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What did you guys get for "Propose a method to determine how quickly a solution of hydrogen peroxide decomposes when stored at a particular temperature"?
Thanks :)
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How did you guys draw the skeletal structure for the molecule in NMR question?
Laws 12 has uploaded a picture of it in an earlier reply :)
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What did you guys get for "Propose a method to determine how quickly a solution of hydrogen peroxide decomposes when stored at a particular temperature"?
Thanks :)
I talked about determining the rate of o2 production for the experiment. We could utilise a separate chamber where the oxygen gas enters and in the chamber a moniter could be employed to determine the amount of oygen that enters the chamber each minute (assuming that all oxygen gas enters the chamber). Do you guys think this feasible enough to gain some marks? It looks like a question where the examiner might accept intriguing option.
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Was the polarity of the electrode( W or Y can’t remember) positive?
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Was the polarity of the electrode( W or Y can’t remember) positive?
I think I recall getting negative. H+ ions were being reduced to form H2 gas at that electrode. Cathode is Negative in an electrolytic cell.
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I think I recall getting negative. H+ ions were being reduced to form H2 gas at that electrode. Cathode is Negative in an electrolytic cell.
Same here
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Same here
double that
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What did you guys get for "Propose a method to determine how quickly a solution of hydrogen peroxide decomposes when stored at a particular temperature"?
Thanks :)
I wrote on how the Oxygen gas created could be extracted, while a timer is used to record the time until no oxygen is found to form.
I not sure if i needed to say this other part, but i also mentioned that one method of seeing when all oxygen is made would be to put extracted oxygen into a combustion reaction with excess fuel, as when no more fuel combusts, all of H2O2 has decomposed.
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For the same question about the electrode being negative in the electrolytic section, what did you guys write for the equation in the alkane electrolyte? Did you guys get OH- ions as products?
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I think you can just measure the beaker every minute or so haha. If a gas is released the beaker weight will decrease.
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By the way, it is possible for the compound on the C-NMR question to be butan-1-amine instead of 2 methyl propan-1-amine?
Cause like, i said the peak at around 60 was the R3C-NH2 and the other one was R-CH2-R.
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By the way, it is possible for the compound on the C-NMR question to be butan-1-amine instead of 2 methyl propan-1-amine?
Cause like, i said the peak at around 60 was the R3C-NH2 and the other one was R-CH2-R.
I believe the C NMR showed 3 peaks which corresponded to 3 carbon environments. Butan-1-amine has four carbon environments whilst the latter option has 3 carbon environments and so I chose the latter option and thats what I did. If those were the two option you wrote for the two structural isomers in the previous part, then you should be correct.
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I think you can just measure the beaker every minute or so haha. If a gas is released the beaker weight will decrease.
True, but my argument is that method assumes O2(g) is the only gas released, which depending of the temperature tested could be incorrect. (some H2O2 could vaporise)
Probably just me overthinking it though.
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Possible for someone to upload a copy of the exam, please?
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Possible for someone to upload a copy of the exam, please?
mods are gonna get ya
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Possible for someone to upload a copy of the exam, please?
Your answer is this, sorry! :)
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mods are gonna get ya
Your answer is this, sorry! :)
Hmm, I guess things have changed since I was last active on these forums - thanks!
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I... I thought I did pretty well on the exam, since I felt happy afterwards, but reading some answers on here made me think otherwise. :o
Anyway, just going to list some questions I had some trouble with;
A systematic error for the electrical calibration? I wrote that the voltage applied would not be exactly as the expected value of 6.0V (but on second thought, that's a random error, isn't it?)
I wasn't sure what limitation was apparent in the chemical calibration, so I just said that bc chemical calibration was conducted immediately afterwards the electrical calibration, change in temperature may be affected.
Also, how do you explain the coenzyme question (how vitamin C interacts physically and chemically with the enzyme to assist in the catalysis of collagen(?))? I assumed you had to include the amino acid that was drawn in part a.) in the answer... but I don't know.
Lastly, before I disappear, that coconut question. Did you have to draw a triglyceride, since it said "show the structure of a triglyceride"? It was strange drawing it with lines running across the page.
tl;dr (sorry)
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A systematic error for the electrical calibration? I wrote that the voltage applied would not be exactly as the expected value of 6.0V (but on second thought, that's a random error, isn't it?)
the thing is, your answer can be both random and systematic, it is random if you explain it in the context of voltage fluctuations but is systematic if you explain it in terms of resistance of electrical equipment. it depends what context it is in.
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Stay tuned - they'll be done by this evening :)
they said ....
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11.375% =11%
I calculated 11.4% but its wrong, cuz it ask for percentage of mass from cellulose so its 34%
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Stay tuned - they'll be done by this evening :)
they said ....
The day isn't over. Remember they are quite generously doing this for free with no strings attached. The least we can do to show our appreciation for their altruistic efforts is be patient.
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The day isn't over. Remember they are quite generously doing this for free with no strings attached. The least we can do to show our appreciation for their altruistic efforts is be patient.
Also, the chemistry exam is WAY more open-ended with its answers than methods and specialist. It'd probably take ages to find of every possible answer for some of the theory questions
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Hey all. Sorry the solutions are taking a long time. The chem exam is massive and there's just a lot to cover. Tonight, we're just going to upload the Section B full answers. We'll provide the answers to Section A, but with no working or explanation. We'll slowly add full solutions for Section A in the next few days. (We're incredibly busy at the moment!)
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I thought it was 2-methyl propan-1-amine as there were 3 carbon environments present, 2-methylpropan-2-amine only has 2. Looks like this
Will you lose the mark if you expanded the NH2 bonds? The data book shows the O-H bond extended but I'm not sure if it only applies to O-H bonds.
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Solutions are up!
Get them here: https://atarnotes.com/forum/index.php?topic=181372.msg1085659#msg1085659
Or get them on our website: twmpublications.com/solutions
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Ended up getting 108-110, am i that bloody stupid for making the stupidest of mistakes by not timing (x4) for the solar panels, not taking into factor the 35% efficiency, saying succinic acid instead of glycerol.... ffs
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Solutions are up!
Get them here: https://atarnotes.com/forum/index.php?topic=181372.msg1085659#msg1085659
Or get them on our website: twmpublications.com/solutions
thanks for your hard work, i appreciate your generosity :)
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Solutions are up!
Get them here: https://atarnotes.com/forum/index.php?topic=181372.msg1085659#msg1085659
Or get them on our website: twmpublications.com/solutions
WOW!!! Thank you so much! Truly amazing work - would have taken AGES to type up chemical structures!
Friendly FYI (zero disrespect, as your work is much appreciated)
1aiii is 2,3 dibromo 4-methyl hexane
2d Oxygen is evolved (not hydrogen)
3bi M(parent) = 73g/mol
5cii m(ethanol) = 11370g, which in then times by 29.6KJ/g (databook)
8cii n(petrodiesel) has not been inputted into the calculator correctly, affecting subsequent working out
9d Both experiments were turned off after 180 sec (identical graphs) to this point. Maybe a stirring issue between Student A and B???
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I think the second isomer given for 3biii is also incorrect. The correct one is drawn, however, for the skeletal formula.
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I think the second isomer given for 3biii is also incorrect. The correct one is drawn, however, for the skeletal formula.
Yes, you are correct :o
It should have a 3C backbone :D
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Hey, could someone please tell me what my study score would roughly be from these scores:
SAC Avg: 80%
Exam Score 70-75%
Good cohort
Thanks :)
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Hey, could someone please tell me what my study score would roughly be from these scores:
SAC Avg: 80%
Exam Score 70-75%
Good cohort
Thanks :)
Hey! If you wish for people to predict study scores please post on the study score prediction thread since this is a thread based solely on chemistry questions. Also for future reference please provide your ranking within the cohort :)
https://atarnotes.com/forum/index.php?topic=138501.0
But with those scores, I think you are looking at around 35-37
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Thoughts on A+/A this year????
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Thoughts on A+/A this year????
To be honest I’d say the same as last year but many will disagree. While most of the exam was pretty easy some questions such as the 4 panel question undoubtedly screwed people over. Also the exam was long..
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Hey all, we've noted the errors you guys have pointed out in the solutions. We'll get to fixing them ASAP.
Just so people know, I'm not doing the Chem and Physics solutions. I'll just be formatting the documents.
I wish I could help go through the Chem solutions but I wasn't that great at chem, so I'm pretty much useless here lol :(
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Hey all, we've noted the errors you guys have pointed out in the solutions.
Just so people know, I didn't write them. I just formatted the document. We'll get to fixing them ASAP.
I wish I could help go through the solutions but I wasn't that great at chem, so I'm pretty much useless here lol :(
Great job with formatting! Thanks for your efforts.
And a huge thanks to the solution writers too! What a bunch of geniuses!
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Great job with formatting! Thanks for your efforts.
And a huge thanks to the solution writers too! What a bunch of geniuses!
Well, I did the solutions for Methods and Specialist. Chem and Physics is done by someone else :)
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Does anyone know if there should be consequential marks for the 4 panel q if we didn't multiply by 4? If so, how many?
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Does anyone know if there should be consequential marks for the 4 panel q if we didn't multiply by 4? If so, how many?
When marking I decided I'd only get one for that. I'm assuming 1 mark for recognition of 4 panels, one for working out and one for the >correct answer<. Probably only get the middle one.
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When marking I decided I'd only get one for that. I'm assuming 1 mark for recognition of 4 panels, one for working out and one for the >correct answer<. Probably only get the middle one.
To be honest I can see assessors giving 2 marks, 1 mark for correct utilisation Faraday's Laws/Equations, 1 mark for correct molar ratio and 1 mark for answer. However, the following 1 mark question based on your previous answer only awards 1 mark so that question requires the correct answer.
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Yeah, what's up with that crap? Such a stupid thing to do...
Hi! The odds are that VCAA will not award the mark for siginificant figures for that question :)
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WOW!!! Thank you so much! Truly amazing work - would have taken AGES to type up chemical structures!
Friendly FYI (zero disrespect, as your work is much appreciated)
1aiii is 2,3 dibromo 4-methyl hexane
2d Oxygen is evolved (not hydrogen)
3bi M(parent) = 73g/mol
5cii m(ethanol) = 11370g, which in then times by 29.6KJ/g (databook)
8cii n(petrodiesel) has not been inputted into the calculator correctly, affecting subsequent working out
9d Both experiments were turned off after 180 sec (identical graphs) to this point. Maybe a stirring issue between Student A and B???
Hi! Thankyou so much for providing this feedback. Most of it was identified and is fixed, a new copy will be uploaded tomorrow! We are so sorry for this confusion for the last question i suspect that the calibration started at 180, not stopped.
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Which one has the lower GI?
My teacher stated there were two possible answers:
1. The shredded pieces would have a higher GI, due to inceased surface area resulting in an increased rate of hydrolysis to produce glucose.
2. Both would have the same GI, due to the large coconut pieces required to be broken down by chewing the chunks into smaller pieces, increasing SA and Therefore Rate of Hydroysis to produce glucose