ATAR Notes: Forum
Archived Discussion => 2012 => Mid-year exams => Exam Discussion => Victoria => Chemistry => Topic started by: Tonychet2 on June 13, 2012, 03:25:15 pm
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link to exam here: VCAA 2012 Chemistry Unit 3 Exam Discussion
1.B
2.C
3.D
4.B
5.D
6.A
7.C
8.D
9.A
10.A
11.A
12.C
13.C
14.B
15.B
16.C
17.D
18.C
19.B
20.D
1ai. glucose
1ii. 2 CH3CH2OH and 2 CO2
1iii. C2H4 (g) + H2O (l) ------H+----> CH3CH2OH
1b) i ) 3 for product A and 1 for product B
ii) Stearic
iii) C18H36O2 (aq) + 26O2 (g) ----> 18CO2(g) + 18 H2O (l)
2a) Tyrosine
b) the lower dot on the 2nd column
c) the Rf values of threonine and alanine are equal in solvent G in chromatogram 1, therefore together they produce 1 spot, making 3 spots total.
the Rf values of threonine and alanine are different in solvent F in chromatogram 2, therefore they will produce different spots in chromatogram 2, making 4 spots total.
3a) H2N-(CH2)6-NH2
b) amide
bii) amide
c) the 2 monomers of nylon contain either 2 carboxyl groups with 0 amino groups or 0 carboxyl groups with 2 amino groups, whereas the monomers of protein contain 1 carboxyl and 1 amino group each. Therefore when condensation polymerisation occurs, the orientation of the amino and carboxyl groups will be different in nylon and protein.
4a) propan-1-ol and propanoic acid
b) CH3CH2OH(l) + CH3CH2COOH (aq) ----H2SO4---> CH3CH2COOCH2CH2CH3 (l) + H2O(l)
c) 1. begin with propanol, 2. oxidise some propanol into propanoic acid using dicromate as catalsyt and in a H+ medium, 3. react propanoic acid with propanol using H2SO4 as catalyst, to produce propyl propanote.
d) gas chromatography, if only one peak occurs, the sample is pure, if the retention time is the same as a known sample of propyl propanoate, it is propyl propanoate.
5a) 2
ii) 3
iii) 6
b) Oxygen and Hydrogen
c) CH3 - CH-OH - CH3
6a) draw graph
ii) 36mg
b) do it yourself lol
7a) PB2+ (aq) + 2I- (aq) ---> PbI2 (s)
ii) to remove any impurities and to remove all excess water
iii) 0.0939g
iv) 0.3313g
b) lead nitrate is highly soluble in water, therefore no precipitate can be extracted
8a) NaOH (aq) + HCL (aq) ---> NaCL(s) + H2O (l)
ii) 0.04mol
iii) 0.00216 mol
iv) 0.0270mol
v) 289g/L
b) lower because a higher amount of titre would be required to neutralise the solution, therefore the n(NaOH) !(not n(HCL) oops wasnt thinking when i wrote this)! that reacted with n(ammonia chloride) will be lower. thus leading to a lower calculated solubility
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any questions feel free to ask note i may be wrong..
n please correct me if im wrong lol
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with 3b wouldn't it be amino and carboxyl because it asks for the function groups?
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link to exam here: VCAA 2012 Chemistry Unit 3 Exam Discussion
8a) NaOH (aq) + HCL (aq) ---> NaCL(s) + H2O (l)
ii) 0.04mol
iii) 0.00216 mol
iv) 0.270mol
v) 289g/L
I think iv) is 0.0270 mol?
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with 3b wouldn't it be amino and carboxyl because it asks for the function groups?
link to exam here: VCAA 2012 Chemistry Unit 3 Exam Discussion
8a) NaOH (aq) + HCL (aq) ---> NaCL(s) + H2O (l)
ii) 0.04mol
iii) 0.00216 mol
iv) 0.270mol
v) 289g/L
I think iv) is 0.0270 mol?
yes i accidently left out a 0, thanks edited
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any questions feel free to ask note i may be wrong..
n please correct me if im wrong lol
Just checked ur soln's against mine, all is fine except:
SAQ1bii - stearic acid must be liquid, cannot combust an aqueous solution.
SAQ4c - H+ is not a catalyst, it's an actual reactant
SAQ6ii - i got 360 mg not 36...(never mind - misread qn. did paper too quickly hahah just scanned it, its 36)
SAQ7aii - you dont need to mention 'impurities' because qn asked why was it heated and weighed rather than washed, but you got the essential point that is to remove all the water in the precipitate
Oh yeah, and NaCl is aqueous.
And the last qn - its NaOH that reacts with ammonium chloride, not HCl :/
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Umm... with the 8b.... since n=cv.... and a larger volume is required to reach the equivalent point.... shouldn't n(HCL) be higher?
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with 3b wouldn't it be amino and carboxyl because it asks for the function groups?
no because the question was
name the functional groups that link the monomers the amide functional group links the monomers? thats how i interpreted it
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Umm... with the 8b.... since n=cv.... and a larger volume is required to reach the equivalent point.... shouldn't n(HCL) be higher?
It is, but that means that there appears to be too much NaOH in excess, meaning there is not much NH4Cl, so calculated solubility is lower.
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any questions feel free to ask note i may be wrong..
n please correct me if im wrong lol
Just checked ur soln's against mine, all is fine except:
SAQ1bii - stearic acid must be liquid, cannot combust an aqueous solution.
SAQ4c - H+ is not a catalyst, it's an actual reactant
SAQ6ii - i got 360 mg not 36...
SAQ7aii - you dont need to mention 'impurities' because qn asked why was it heated and weighed rather than washed, but you got the essential point that is to remove all the water in the precipitate
ok will edit it and for question 6) the concentration off the graph was 360mg / L however each tablet was dissolved in 100ml so 36mg is in each tablet
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SAQ6ii - i got 360 mg not 36...
It's 360mg in 1L. It's asking for how much in 100ml, so it's 36mg.
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SAQ6ii - i got 360 mg not 36...
It's 360mg in 1L. It's asking for how much in 100ml, so it's 36mg.
100 mL? Lemme read qn again...right, i get ya. yeah 36 mg.
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what mark do u think i will get for those answers?? i got one multiple choice wrong rest of those was what i wrote in the exam
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with 3b wouldn't it be amino and carboxyl because it asks for the function groups?
no because the question was
name the functional groups that link the monomers the amide functional group links the monomers? thats how i interpreted it
Shouldn't it be amide for nylon, peptide for the protein "polymer"
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Isn't NaCl aqueous?
EDIT: Could you write OH-(aq) + H+(aq) => H2O(l) for the neutralisation?
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with 3b wouldn't it be amino and carboxyl because it asks for the function groups?
no because the question was
name the functional groups that link the monomers the amide functional group links the monomers? thats how i interpreted it
Shouldn't it be amide for nylon, peptide for the protein "polymer"
amide for both, they are both condensation reactions and have amide functional group
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with 3b wouldn't it be amino and carboxyl because it asks for the function groups?
no because the question was
name the functional groups that link the monomers the amide functional group links the monomers? thats how i interpreted it
I actually think VCAA might end up accepting both answers... Both are correct answers to what, in my opinion, are valid interpretations of the question.
EDIT:
amide for both, they are both condensation reactions and have amide functional group
A peptide bond is just an amide bond in a biological context. They should accept either "amide and peptide" or "amide and amide".
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with 3b wouldn't it be amino and carboxyl because it asks for the function groups?
no because the question was
name the functional groups that link the monomers the amide functional group links the monomers? thats how i interpreted it
Shouldn't it be amide for nylon, peptide for the protein "polymer"
Amide is fine for both. Peptides are a type of amide.
And vnguyen you can that's fine too.
Tony i'd say 72/77.
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Isn't NaCl aqueous?
EDIT: Could you write OH-(aq) + H+(aq) => H2O(l) for the neutralisation?
nacl is salt so its solid
and yes
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Isn't NaCl aqueous?
EDIT: Could you write OH-(aq) + H+(aq) => H2O(l) for the neutralisation?
nacl is salt so its solid
and yes
NaCl is soluble in water - it'd be aqueous.
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with 3b wouldn't it be amino and carboxyl because it asks for the function groups?
no because the question was
name the functional groups that link the monomers the amide functional group links the monomers? thats how i interpreted it
Shouldn't it be amide for nylon, peptide for the protein "polymer"
Amide is fine for both. Peptides are a type of amide.
And vnguyen you can that's fine too.
Tony i'd say 72/77.
?really yay!! but isnt it out of 75?
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Would it be ok to use sodium carbonate to test if it was only propyl propanoate?
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Isn't NaCl aqueous?
EDIT: Could you write OH-(aq) + H+(aq) => H2O(l) for the neutralisation?
nacl is salt so its solid
and yes
NaCl is soluble in water - it'd be aqueous.
oh yeahhhh dam..
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with 3b wouldn't it be amino and carboxyl because it asks for the function groups?
no because the question was
name the functional groups that link the monomers the amide functional group links the monomers? thats how i interpreted it
Shouldn't it be amide for nylon, peptide for the protein "polymer"
Amide is fine for both. Peptides are a type of amide.
And vnguyen you can that's fine too.
Tony i'd say 72/77.
?really yay!! but isnt it out of 75?
Was it out of 75? Exam cover said 77!
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i thought the exam cover said 75 because i remember reading the 8 questions worth 55 marks but im not 100% sure.. dam that means i only got 70 :( is that still a high a+?
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Isn't NaCl aqueous?
EDIT: Could you write OH-(aq) + H+(aq) => H2O(l) for the neutralisation?
I wrote that too.
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Found it too easy. Already lost like 10 marks from lack of care. Also, a **** video went off through half the exam so we were treated to an earful of a man and his girlfriend as I was doing that stupid H NMR question. Why did I put down 1- propanol. WHY.
True story.
Chemistry FML.
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Found it too easy. Already lost like 10 marks from lack of care. Also, a **** video went off through half the exam so we were treated to an earful of a man and his girlfriend.
True story.
Chemistry FML.
hahahaha at the video! omg lol
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Most retarded exam ever. Normally there's a really high pitched weird noise in that room. Now we know that room is haunted by weirdness q.q
Our supervisor was BRB let's kill that video, sorry peoples.
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I think I'm around 75-80%
If someone had told me that I was going to get that before I started, I would've laughed at their stupidity 8) ;D
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I think the main problem with this exam was that, if people found it extremely easy, they could've rushed through it without adequately checking.
I was so paranoid about there being tricks for each question that I didn't have time to check through all of my solutions after I had finished the exam.
The solubility question, I got 289 the first time and I was like, "that's a pretty big number". Paranoid that I did something wrong, I crossed my working out from the previous question and did it through a different method and got the same answer. So I wasted time crossing out my working for nothing basically =="
I'd say that the exam is on par with the 2008 and 2010 exams, maybe even easier.
There was a VCAA supervisor who looked like Dumbledore at our school. :)
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I'd say that the exam is on par with the 2008 and 2010 exams, maybe even easier.
There was a VCAA supervisor who looked like Dumbledore at our school. :)
Anyone know what was the A+ cut-off score for 2010/2008??
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2008 was 87%, 2010 was 89%.
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Honestly I reckon the cutoff will be less than it was for those two years. I did perfectly on those two exams because they were pretty straightforward with no questions to really trip you up, whereas today there were a number of questions which probably exposed the lack of solidarity in my working. And I reckon (or at least I hope) that will have been a common theme throughout the state.
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1.B
2.C
3.D
4.B
5.D
6.A
7.C
8.D
9.A
10.A
11.A
12.C
13.C
14.B
15.B
16.C
17.D
18.C
19.B
20.D
1ai. Glucose (or beta glucose if you prefer)
1ii. 2CH3CH2OH(aq) + 2CO2(g). I antagonistically wrote enzymes over the reaction arrow too, which in hindsight was probably not a particularly bright idea.
1iii. C2H4(g) + H2O(g) ------H3PO4----> CH3CH2OH(l)
1bi) 3 fatty acids and 1 glycerol
ii) Stearic acid
iii) C18H36O2(l) + 26O2(g) ----> 18CO2(g) + 18 H2O(g)
2a) Tyrosine
b) The lower of the two dots in the middle.
c) Solvent G did not separate alanine and threonine and hence they produced only a single spot with the same Rf value, and three spots for Chromatogram I overall. Solvent F then differentiated between alanine and threonine so that they both produced individual spots with different Rf values. Whilst alanine and arginine had identical Rf values under Solvent F they had been separated by Solvent G and hence Chromatogram II had an additional spot and four spots overall.
3a) H2N-(CH2)6-NH2
b) Amide
bii) Amide/Peptide
c) Ceebs typing this up right now.
4a) Propan-1-ol and Propanoic acid
b) CH3CH2OH(l) + CH3CH2COOH (l) ----H2SO4(l)---> CH3CH2COOCH2CH2CH3 (l) + H2O(l)
c) Obtain a pure sample of propan-1-ol. Oxidise half of this sample using acidified dichromate to obtain propanoic acid. React propanoic acid with the remaining half of propan-1-ol in the presence of concentrated sulfuric acid to obtain propyl propanoate. Distil this product to obtain pure propyl propanaote.
d) Obtain an IR spectrum of the product. If it does not depict an O-H (acid) absorption band or O-H (alcohol) absorption band it can be said to be pure as any contamination from the reactants propanoic acid and propan-1-ol respectively would result in these absorption bands being present in the IR spectrum of the final product.
5a) 2
ii) 3
iii) 6
b) Oxygen and Hydrogen (Although VCAA may accept and even prefer O-H)
c) <Insert Propan-2-ol structure>
6a) You'll have to draw your own graph :P
ii) 36mg
b) UV-Visible Spectroscopy: The level of absorbance of certain wavelengths of light in the UV-Visible region can be used to assess the concentration of compounds which absorb in that specific wavelength. Throw in something about electrons moving to a higher energy level.
7a) Pb2+ aq) + 2I-(aq) ---> PbI2(s)
ii) To ensure that all water had been removed from the precipitate and was not contributing to the mass weighed.
iii) 0.0939g
iv) 0.331g
b) Nitrates are soluble in water with lead (II) cations and vice-versa and hence no precipitate was formed.
8a) NaOH(aq) + HCL(aq) ---> NaCL(aq) + H2O (l)
ii) 0.0400mol
iii) 0.00216mol
iv) 0.0270mol
v) 289g/L
b)Lower because a greater titre of HCl would be required resulting in the amount of NaOH in excess being calculated as greater than its actual value and the amount reacted with ammonium chloride to be less than its actual value. Hence the mass of ammonium chloride dissolved in solution will appear to be less than it really is.
DISCLAIMER: I didn't answer the questions exactly like this in the actual exam, unfortunately. A few of my response questions here are less detailed and would probably not obtain full marks.
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Honestly I reckon the cutoff will be less than it was for those two years. I did perfectly on those two exams because they were pretty straightforward with no questions to really trip you up, whereas today there were a number of questions which probably exposed the lack of solidarity in my working. And I reckon (or at least I hope) that will have been a common theme throughout the state.
people woulda choked on the propan-1-ol question and drawing the polymer of the alkene addition reaction im geussing
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Honestly I reckon the cutoff will be less than it was for those two years. I did perfectly on those two exams because they were pretty straightforward with no questions to really trip you up, whereas today there were a number of questions which probably exposed the lack of solidarity in my working. And I reckon (or at least I hope) that will have been a common theme throughout the state.
people woulda choked on the propan-1-ol question and drawing the polymer of the alkene addition reaction im geussing
Perhaps.
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wasnt carboxyl group a functional group for the nylon question?
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wasnt carboxyl group a functional group for the nylon question?
No because the monomers were linked via amide groups, which arose from reactions bewteen carboxyl groups and amino groups. So they weren't present anymore since after condensation a water molecules comes out, etc.
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wasnt carboxyl group a functional group for the nylon question?
No because the monomers were linked via amide groups, which arose from reactions bewteen carboxyl groups and amino groups. So they weren't present anymore since after condensation a water molecules comes out, etc.
this.
howd u find the exam charmander?
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the question was: "name the functional groups that link the monomers in nylon and protein"
i perceived that as, name the functional groups in the monomers, that link up to make nylon and protein.
:S
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wasnt carboxyl group a functional group for the nylon question?
No because the monomers were linked via amide groups, which arose from reactions bewteen carboxyl groups and amino groups. So they weren't present anymore since after condensation a water molecules comes out, etc.
this.
howd u find the exam charmander?
During the exam I thought it was really difficult but that I'd get managed to get everything right. Afterwards realised that it was quite straightforward but I'd dropped a good number of marks due to rather mundane errors. Yourself?
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wasnt carboxyl group a functional group for the nylon question?
No because the monomers were linked via amide groups, which arose from reactions bewteen carboxyl groups and amino groups. So they weren't present anymore since after condensation a water molecules comes out, etc.
this.
howd u find the exam charmander?
During the exam I thought it was really difficult but that I'd get managed to get everything right. Afterwards realised that it was quite straightforward but I'd dropped a good number of marks due to rather mundane errors. Yourself?
i got question 5 in the mc wrong, everything else i wrote here is what i put on the exam, on which questions did u make errors did u make if u dont mind me asking???
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To be honest I'd rather not talk about them :/ Nothing personal, I just can't don't feel like acknowledging them outside of my mind if you know what I mean.
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To be honest I'd rather not talk about them :/ Nothing personal, I just can't don't feel like acknowledging them outside of my mind if you know what I mean.
ok no problem privacy respected!
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So do you think OH-(aq) + HCl(aq) ---> H20(l) + Cl- (aq) would be acceptable for question 8a? (Don't ask me why i decided to write half an ionic equation -.-)
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ds anyone have the question n answer booklet for tdays exam??
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ds anyone have the question n answer booklet for tdays exam??
questions are : VCAA 2012 Chemistry Unit 3 Exam Discussion
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Isn't MC
i had
5) A
12) C?
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Isn't MC 5 A)?
I put the option that had I and III only (this is the amino acid question right?). It couldn't be II because that would state that hydrogen bonds could occur between any C=O and N-H functional groups, and I found some amino acids that had those functional groups in their side chains.
How much do you think we could have dropped on this exam to be still in the running for a 50? I think I've stuffed up on one question, that stupid solubility one. It was annoying because technically some PbI2 was still dissolved in solution, though it's correct to state you can't really calculate because you don't know how much KI was added. Dumb question.
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Isn't MC 5 A)?
I put the option that had I and III only (this is the amino acid question right?). It couldn't be II because that would state that hydrogen bonds could occur between any C=O and N-H functional groups, and I found some amino acids that had those functional groups in their side chains.
How much do you think we could have dropped on this exam to be still in the running for a 50? I think I've stuffed up on one question, that stupid solubility one. It was annoying because technically some PbI2 was still dissolved in solution, though it's correct to state you can't really calculate because you don't know how much KI was added. Dumb question.
i put down A personally also, but everyone seemed to agree with D so in these i put D
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wb 12, i thought retention time stays the same :'(
must have read it wrong
my bad
Q 5...
i really think it's A
though it's a bit ambigous as they can be in z side chains, maybe 2 correct sols?
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Isn't MC
i had
5) A
12) C?
Isn't MC 5 A)?
I put the option that had I and III only (this is the amino acid question right?). It couldn't be II because that would state that hydrogen bonds could occur between any C=O and N-H functional groups, and I found some amino acids that had those functional groups in their side chains.
How much do you think we could have dropped on this exam to be still in the running for a 50? I think I've stuffed up on one question, that stupid solubility one. It was annoying because technically some PbI2 was still dissolved in solution, though it's correct to state you can't really calculate because you don't know how much KI was added. Dumb question.
it was secondary structure, not tertiary so z-group interactions dont matter i think.
secondary structure is the hydrogen bonding between amide groups. so i think B was right.
12 was defintely C!
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Isn't MC
i had
5) A
12) C?
12 was C. 5 was D because it's not technically false to say that the secondary structure involves hydrogen bonds between N-H and C-O groups. Because that is the case. If it had said that it involved hydrogen bonds between all N-H and C-O that would be untrue.
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wb 12, i thought retention time stays the same :'(
must have read it wrong
my bad
Q 5...
i really think it's A
though it's a bit ambigous as they can be in z side chains, maybe 2 correct sols?
I think the option should have said C=O and N-H functional groups in the peptide linkage or something. A should definitely be correct, not sure if they should accept D though.
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gg :'(
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Would the answer for Question 1 a i be galactose because of the rearrangement of carbon fours hydroxyl group from positioned down to a up position? :-\ :-\ :o
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Isn't MC
i had
5) A
12) C?
12 was C. 5 was D because it's not technically false to say that the secondary structure involves hydrogen bonds between N-H and C-O groups. Because that is the case. If it had said that it involved hydrogen bonds between all N-H and C-O that would be untrue.
It would be false, because the secondary structure isn't maintained by hydrogen bonds between N-H and C-O groups in the side chains. By saying between N-H and C-O groups, it still includes those side chains. So I guess they might have to accept two answers then.
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wb 12, i thought retention time stays the same :'(
must have read it wrong
my bad
Q 5...
i really think it's A
though it's a bit ambigous as they can be in z side chains, maybe 2 correct sols?
I think the option should have said C=O and N-H functional groups in the peptide linkage or something. A should definitely be correct, not sure if they should accept D though.
It said ' in the secondary structure...'
so that would automatically imply hydrogen bonding b/w amide groups! which i believe option II satisfies?
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Would the answer for Question 1 a i be galactose because of the rearrangement of carbon fours hydroxyl group from positioned down to a up position? :-\ :-\ :o
No, cellulose is comprised of glucose monomers.
The reason why the hydroxyl group is down to up is because cellulose is contains beta-1,4-glycosidic linkages, so alternating glucose molecules would be flipped (look at the ring Oxygen, you can see how it flips as well)
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Would the answer for Question 1 a i be galactose because of the rearrangement of carbon fours hydroxyl group from positioned down to a up position? :-\ :-\ :o
i think its just general fact that cellulose is a polymer of glucose.
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could you write mass spec for 4d?
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would the answer be B for question 6 on Multiple choice?
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wb 12, i thought retention time stays the same :'(
must have read it wrong
my bad
Q 5...
i really think it's A
though it's a bit ambigous as they can be in z side chains, maybe 2 correct sols?
I think the option should have said C=O and N-H functional groups in the peptide linkage or something. A should definitely be correct, not sure if they should accept D though.
It said ' in the secondary structure...'
so that would automatically imply hydrogen bonding b/w amide groups! which i believe option II satisfies?
Actually, the full statement is "The secondary structure of a protein is the result of hydrogen bonding between -NH and -CO groups".
Bonding between -NH and -CO groups in sidechains doesn't result in the maintenance of the secondary structure, that's tertiary structure. :/
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Isn't MC
i had
5) A
12) C?
12 was C. 5 was D because it's not technically false to say that the secondary structure involves hydrogen bonds between N-H and C-O groups. Because that is the case. If it had said that it involved hydrogen bonds between all N-H and C-O that would be untrue.
It would be false, because the secondary structure isn't maintained by hydrogen bonds between N-H and C-O groups in the side chains. By saying between N-H and C-O groups, it still includes those side chains. So I guess they might have to accept two answers then.
It doesn't include side chains at all. It mentioned only the nature of the bonding and from which atoms it stemmed, not from whereabouts on the molecule those atoms were. Regardless, hydrogen bonding in the tertiary structure doesn't occur between N-H and C=O groups.
I was so tempted to write beta glucose for that question but I couldn't remember what the symbol for beta looked like haha.
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and for the average mass of Iron question, could you have found the average of the four concentrations (100-400) and used that to find the mass?
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hey thushan, you know for ques 13 of multiple choice, shouldn't it be 2.50M, because c(H) = 10 M from the original,
the volume is changed from 15mL to 60mL, so it's diluted by a factor of 4, what I did was dividing 10 by 4 , and i got 2.50 M
or did I get it wrong?
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Question 6aii)30mg
At 0mg/l the absorbance value was 0.06 therefore you need to subtract this from the average absorbance value.
interesting point. and to the other person use c1v1 = c2v2 to solve for c2,
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Isn't MC
i had
5) A
12) C?
12 was C. 5 was D because it's not technically false to say that the secondary structure involves hydrogen bonds between N-H and C-O groups. Because that is the case. If it had said that it involved hydrogen bonds between all N-H and C-O that would be untrue.
It would be false, because the secondary structure isn't maintained by hydrogen bonds between N-H and C-O groups in the side chains. By saying between N-H and C-O groups, it still includes those side chains. So I guess they might have to accept two answers then.
It doesn't include side chains at all. It mentioned only the nature of the bonding and from which atoms it stemmed, not from whereabouts on the molecule those atoms were.
I was so tempted to write beta glucose for that question but I couldn't remember what the symbol for beta looked like haha.
Yeah but because it doesn't mention WHERE those atoms are, it doesn't rule out the atoms in the side chains. Secondary structure is specifically maintained by those atoms in the peptide linkage, it can't be from anywhere else in the polypeptide.
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hey thushan, you know for ques 13 of multiple choice, shouldn't it be 2.50M, because c(H) = 10 M from the original,
the volume is changed from 15mL to 60mL, so it's diluted by a factor of 4, what I did was dividing 10 by 4 , and i got 2.50 M
or did I get it wrong?
The volume is changed from 15mL to 75mL (added 60)
c1v1 = c2v2
c2 = (10*15)/75 = 2M, C
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Isn't MC
i had
5) A
12) C?
12 was C. 5 was D because it's not technically false to say that the secondary structure involves hydrogen bonds between N-H and C-O groups. Because that is the case. If it had said that it involved hydrogen bonds between all N-H and C-O that would be untrue.
It would be false, because the secondary structure isn't maintained by hydrogen bonds between N-H and C-O groups in the side chains. By saying between N-H and C-O groups, it still includes those side chains. So I guess they might have to accept two answers then.
It doesn't include side chains at all. It mentioned only the nature of the bonding and from which atoms it stemmed, not from whereabouts on the molecule those atoms were.
I was so tempted to write beta glucose for that question but I couldn't remember what the symbol for beta looked like haha.
Yeah but because it doesn't mention WHERE those atoms are, it doesn't rule out the atoms in the side chains. Secondary structure is specifically maintained by those atoms in the peptide linkage, it can't be from anywhere else in the polypeptide.
That's a very fair point, hopefully they will award marks for both A and D
Edit: But you would be pretty lucky if they give you a mark for A. The statement is 100% true in that the result of the secondary structure IS FROM H-bonding between -NH and -CO groups. It doesn't necessarily have to say 'in the peptide bonds of the amino acids' or something to that effect.
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wb 12, i thought retention time stays the same :'(
must have read it wrong
my bad
Q 5...
i really think it's A
though it's a bit ambigous as they can be in z side chains, maybe 2 correct sols?
I think the option should have said C=O and N-H functional groups in the peptide linkage or something. A should definitely be correct, not sure if they should accept D though.
It said ' in the secondary structure...'
so that would automatically imply hydrogen bonding b/w amide groups! which i believe option II satisfies?
Actually, the full statement is "The secondary structure of a protein is the result of hydrogen bonding between -NH and -CO groups".
Bonding between -NH and -CO groups in sidechains doesn't result in the maintenance of the secondary structure, that's tertiary structure. :/
when you say 'sidechain' are you referring to Z'group? or the Amino and carboxyl groups on AA's?
sec. structure for me is defined as the coiling of the polypeptide strand due to H-bonding between amide groups.
-NH and -CO groups, as it says in the question are bonded via hydrogen bonding in the sec. structure, thus making amide/peptide linkage.
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Isn't MC
i had
5) A
12) C?
12 was C. 5 was D because it's not technically false to say that the secondary structure involves hydrogen bonds between N-H and C-O groups. Because that is the case. If it had said that it involved hydrogen bonds between all N-H and C-O that would be untrue.
It would be false, because the secondary structure isn't maintained by hydrogen bonds between N-H and C-O groups in the side chains. By saying between N-H and C-O groups, it still includes those side chains. So I guess they might have to accept two answers then.
It doesn't include side chains at all. It mentioned only the nature of the bonding and from which atoms it stemmed, not from whereabouts on the molecule those atoms were.
I was so tempted to write beta glucose for that question but I couldn't remember what the symbol for beta looked like haha.
Yeah but because it doesn't mention WHERE those atoms are, it doesn't rule out the atoms in the side chains. Secondary structure is specifically maintained by those atoms in the peptide linkage, it can't be from anywhere else in the polypeptide.
What you're essentially doing then is saying that statement II was not true. But it is true.
Hydrogen bonding in the tertiary structure occurs between other groups too (hydroxyls, etc) and I'm not entirely sure that amines and carboxys do form hydrogen bonds in the tertiary structure.
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Question 6aii)30mg
At 0mg/l the absorbance value was 0.06 therefore you need to subtract this from the average absorbance value.
Mmmm yes but it depends what graph you're using.
If you subtracted 0.06 from all your variables, and you draw your graph through the origin, you'll end up with the same results I think? Because if your graph doesnt' run through the origin, you don't minus the 0.06, at least I'm pretty sure you don't have to.
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4) c) you need to obtain PURE propyl probanoate so you need to do fractional distillation to get the pure form.
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Isn't MC
i had
5) A
12) C?
12 was C. 5 was D because it's not technically false to say that the secondary structure involves hydrogen bonds between N-H and C-O groups. Because that is the case. If it had said that it involved hydrogen bonds between all N-H and C-O that would be untrue.
It would be false, because the secondary structure isn't maintained by hydrogen bonds between N-H and C-O groups in the side chains. By saying between N-H and C-O groups, it still includes those side chains. So I guess they might have to accept two answers then.
It doesn't include side chains at all. It mentioned only the nature of the bonding and from which atoms it stemmed, not from whereabouts on the molecule those atoms were.
I was so tempted to write beta glucose for that question but I couldn't remember what the symbol for beta looked like haha.
Yeah but because it doesn't mention WHERE those atoms are, it doesn't rule out the atoms in the side chains. Secondary structure is specifically maintained by those atoms in the peptide linkage, it can't be from anywhere else in the polypeptide.
What you're essentially doing then is saying that statement II was not true. But it is true.
Hydrogen bonding in the tertiary structure occurs between other groups too (hydroxyls, etc) and I'm not entirely sure that amines and carboxys do form hydrogen bonds in the tertiary structure.
It would be true if they had stated it was only those atoms in the peptide groups. Yes it is maintained by hydrogen bonds between -NH and -CO bonds, but if hydrogen bonds form between those functional groups in the Z-group of amino acids, then those hydrogen bonds don't maintain the secondary structure, they maintain the tertiary structure.
So really, that statement is only partially true. They should accept both A and D.
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Isn't MC
i had
5) A
12) C?
12 was C. 5 was D because it's not technically false to say that the secondary structure involves hydrogen bonds between N-H and C-O groups. Because that is the case. If it had said that it involved hydrogen bonds between all N-H and C-O that would be untrue.
It would be false, because the secondary structure isn't maintained by hydrogen bonds between N-H and C-O groups in the side chains. By saying between N-H and C-O groups, it still includes those side chains. So I guess they might have to accept two answers then.
It doesn't include side chains at all. It mentioned only the nature of the bonding and from which atoms it stemmed, not from whereabouts on the molecule those atoms were.
I was so tempted to write beta glucose for that question but I couldn't remember what the symbol for beta looked like haha.
Yeah but because it doesn't mention WHERE those atoms are, it doesn't rule out the atoms in the side chains. Secondary structure is specifically maintained by those atoms in the peptide linkage, it can't be from anywhere else in the polypeptide.
What you're essentially doing then is saying that statement II was not true. But it is true.
Hydrogen bonding in the tertiary structure occurs between other groups too (hydroxyls, etc) and I'm not entirely sure that amines and carboxys do form hydrogen bonds in the tertiary structure.
It would be true if they had stated it was only those atoms in the peptide groups. Yes it is maintained by hydrogen bonds between -NH and -CO bonds, but if hydrogen bonds form between those functional groups in the Z-group of amino acids, then those hydrogen bonds don't maintain the secondary structure, they maintain the tertiary structure.
So really, that statement is only partially true. They should accept both A and D.
I don't think hydrogen bonds do occur between those functional groups in the tertiary structure though. Not certain though but it may just be other groups.
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Isn't MC
i had
5) A
12) C?
12 was C. 5 was D because it's not technically false to say that the secondary structure involves hydrogen bonds between N-H and C-O groups. Because that is the case. If it had said that it involved hydrogen bonds between all N-H and C-O that would be untrue.
It would be false, because the secondary structure isn't maintained by hydrogen bonds between N-H and C-O groups in the side chains. By saying between N-H and C-O groups, it still includes those side chains. So I guess they might have to accept two answers then.
It doesn't include side chains at all. It mentioned only the nature of the bonding and from which atoms it stemmed, not from whereabouts on the molecule those atoms were.
I was so tempted to write beta glucose for that question but I couldn't remember what the symbol for beta looked like haha.
Yeah but because it doesn't mention WHERE those atoms are, it doesn't rule out the atoms in the side chains. Secondary structure is specifically maintained by those atoms in the peptide linkage, it can't be from anywhere else in the polypeptide.
What you're essentially doing then is saying that statement II was not true. But it is true.
Hydrogen bonding in the tertiary structure occurs between other groups too (hydroxyls, etc) and I'm not entirely sure that amines and carboxys do form hydrogen bonds in the tertiary structure.
It would be true if they had stated it was only those atoms in the peptide groups. Yes it is maintained by hydrogen bonds between -NH and -CO bonds, but if hydrogen bonds form between those functional groups in the Z-group of amino acids, then those hydrogen bonds don't maintain the secondary structure, they maintain the tertiary structure.
So really, that statement is only partially true. They should accept both A and D.
I don't think hydrogen bonds do occur between those functional groups in the tertiary structure though. Not certain though but it may just be other groups.
Hydrogen bonds can form between them, and hydrogen bonds can form else where. Those functional groups share the same dipole properties as they do in the peptide linkage, and thus hydrogen bonds can still form.
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Probably haha. But honestly I don't think VCAA will except two answers. I'm happy to be proven wrong (just so long as it is two answers and not just A :P).
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it should really be two answers.... really ambiguous
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Probably haha. But honestly I don't think VCAA will except two answers. I'm happy to be proven wrong (just so long as it is two answers and not just A :P).
They can accept two answers! :D They've done it before for multiple choice. I think it's too ambiguous for them to accept just D or just A. They stuffed up.
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^ Almost all the top students at our school put down A, minus charmanderp cos hes a chemistry god.
I put A cos I was like... not sure is rly easy or trick question and i was like I got tricked on a similar question during practice exams (couldve been tertiary strucutre hydrogen bonding) and ultiamtely went with A
-sigh!
the dream is dead :p
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^ Almost all the top students at our school put down A, minus charmanderp cos hes a chemistry god.
I put A cos I was like... not sure is rly easy or trick question and i was like I got tricked on a similar question during practice exams (couldve been tertiary strucutre hydrogen bonding) and ultiamtely went with A
-sigh!
the dream is dead :p
Haha I confer any god status to you, sounds like you tore the exam up otherwise.
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5 is most probably D. VCAA might be very unlikely to accept A as well. When taken for its pure meaning, statement II is correct. If the point that secondary structure only involves H bonds between amide sections of the amino acid chain wasn't known, the question would have definetely seemed ambiguous though :/
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Probably haha. But honestly I don't think VCAA will except two answers. I'm happy to be proven wrong (just so long as it is two answers and not just A :P).
They can accept two answers! :D They've done it before for multiple choice. I think it's too ambiguous for them to accept just D or just A. They stuffed up.
They can and I hope they do for your sake but I think the previous examples were slightly different. They were due to lack of details about a certain experiment rather than grey areas.
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from the way it's phrased i think it's implying that it's ONLY from the...
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5 is most probably D. VCAA might be very unlikely to accept A as well. When taken for its pure meaning, statement II is correct. If the point that secondary structure only involves H bonds between amide sections of the amino acid chain wasn't known, the question would have definetely seemed ambiguous though :/
I would agree
Like sure it isn't the -NH and -CO groups on the same amide, but secondary structure is indeed the bonding between -NH and -CO groups of different peptide linkages. The statement is definitely true, so it should be D. It can't be A cos you'd be saying the statement is false.
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5 is most probably D. VCAA might be very unlikely to accept A as well. When taken for its pure meaning, statement II is correct. If the point that secondary structure only involves H bonds between amide sections of the amino acid chain wasn't known, the question would have definetely seemed ambiguous though :/
I would agree
Like sure it isn't the -NH and -CO groups on the same amide, but secondary structure is indeed the bonding between -NH and -CO groups of different peptide linkages. The statement is definitely true, so it should be D. It can't be A cos you'd be saying the statement is false.
But there are amino acids that have -NH and -CO in their side groups (Z groups) and any hydrogen bonding between them maintains the tertiary structure and not the secondary. So statement II is not entirely true, it needs to be more specific.
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5 is most probably D. VCAA might be very unlikely to accept A as well. When taken for its pure meaning, statement II is correct. If the point that secondary structure only involves H bonds between amide sections of the amino acid chain wasn't known, the question would have definetely seemed ambiguous though :/
I would agree
Like sure it isn't the -NH and -CO groups on the same amide, but secondary structure is indeed the bonding between -NH and -CO groups of different peptide linkages. The statement is definitely true, so it should be D. It can't be A cos you'd be saying the statement is false.
But there are amino acids that have -NH and -CO in their side groups (Z groups) and any hydrogen bonding between them maintains the tertiary structure and not the secondary. So statement II is not entirely true, it needs to be more specific.
It could be more specific but that doesn't make it any less true or aphoristic. There's really no such thing as 'entirely true' - you can't really fault that statement. To agree with the statement sats that hydrogen bonding between NH and CO groups does maintain the secondary structure and to disagree says that hydrogen bonding between NH and CO groups does not maintain the secondary structure. Obviously only the former is true.
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I drew the graph starting at 0 instead of .06 absorbance for some stupid reason!!! I used that date to find the mg, how many marks will I lose out of the maximum four??
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I drew the graph starting at 0 instead of .06 absorbance for some stupid reason!!! I used that date to find the mg, how many marks will I lose out of the maximum four??
you'll get consequential, so at least 1, but maybe 2.
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Thanks heaps!
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For 3b, name the functional groups that link the monomers, will they accept ether linkages as the answer?
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for question 4C of Section B didn't you need to include fractional distillation? it asked for a pure sample of propyl propanoate and the reaction of 1-propanol with propanoic acid isn't a 100% reaction so you'd have some reagents left over, you'd need to separate the ester from the left-over acid/alcohol and the water that's produced with it... no?
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For 3b, name the functional groups that link the monomers, will they accept ether linkages as the answer?
there are no ether linkages.
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for question 4C of Section B didn't you need to include fractional distillation? it asked for a pure sample of propyl propanoate and the reaction of 1-propanol with propanoic acid isn't a 100% reaction so you'd have some reagents left over, you'd need to separate the ester from the left-over acid/alcohol and the water that's produced with it... no?
yes probably , crap there goes another mark... hoping for 73/75 now lol
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for question 4C of Section B didn't you need to include fractional distillation? it asked for a pure sample of propyl propanoate and the reaction of 1-propanol with propanoic acid isn't a 100% reaction so you'd have some reagents left over, you'd need to separate the ester from the left-over acid/alcohol and the water that's produced with it... no?
yes probably , crap there goes another mark... hoping for 73/75 now lol
No because the question was about verifying that what we had was pure. Not how we would make it pure. Mentioning fractional distillation at that stage would be irrelevant.
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for question 4C of Section B didn't you need to include fractional distillation? it asked for a pure sample of propyl propanoate and the reaction of 1-propanol with propanoic acid isn't a 100% reaction so you'd have some reagents left over, you'd need to separate the ester from the left-over acid/alcohol and the water that's produced with it... no?
yes probably , crap there goes another mark... hoping for 73/75 now lol
No because the question was about verifying that what we had was pure. Not how we would make it pure. Mentioning fractional distillation at that stage would be irrelevant.
oh yeah thats right, woot might be able to get 74 if markers arent harsh
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Hey guys, with question 4d, do you think TLC would be an acceptable answer? My reasoning is that if only one spot shows up on a chromatogram then it should be considered pure. What do you guys think?
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There's a chance that not all the substances would show up in a TLC even if they were present, as they might be colourless. Normally we'd add ninhydrin or develop it under UV light but again these might not work for all substances, including propyl propanoate, propan-1-ol and propanoic acid.
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Well, hopefully the examiners don't have as much knowledge as you do and accept the answer :D
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for question 4C of Section B didn't you need to include fractional distillation? it asked for a pure sample of propyl propanoate and the reaction of 1-propanol with propanoic acid isn't a 100% reaction so you'd have some reagents left over, you'd need to separate the ester from the left-over acid/alcohol and the water that's produced with it... no?
yes probably , crap there goes another mark... hoping for 73/75 now lol
No because the question was about verifying that what we had was pure. Not how we would make it pure. Mentioning fractional distillation at that stage would be irrelevant.
In 4C you had to mention how to make it pure. The reaction between propanoic acid and 1-propanol produced water, and thus pure propyl propanoate wasn't produce. The question was worth 3 marks. 1 mark for making propanoic acid, 1 mark for making the ester, and 1 mark for obtaining a pure sample of the ester.
Pure was bolded guys. It's what made fractional distillation necessary.
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i said HPLC (lol)
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was the ester a solid? could you have said dry off the water lol?
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For stearic acid the state should be (s) since it is saturated? right???
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Hey guys, this is probably gonna be a weird question...but with Q7 of MC, the one about enzymes, did you not find it a bit ambiguous? :P
Because one of the options talked about 'the substrate forms bonds with the active site', but it didn't specify what bonds...like, it could have been permanent bonds, or temporary bonds, or anything!
And if it were PERMANENT bonds, then that statement would have been wrong...meaning option A would have been correct. The reason its concerning me more is because in a previous VCAA exam (i think 2009), in a MC question similar to these, they talked about enzymes specifically forming TEMPORARY ion-dipole bonds, or some shiz like that...
I'm probably reading too much into it, but yah :)
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Bonds are bonds are bonds are bonds are bonds are bonds are bonds are bonds are bonds (not the underwear brand btw)! The fact that it forms any bonds at all probably validates that statement. I think the trick intended there was for students to think that the substrate fit into the enzyme simply because its shape was complementary to the active site, where as it was this and inter-molecular bonding.
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What do you guys think an A+ will be?
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Question 1b SA
Anyone else noticed the C=C instead of a C=O on the bottom third of the triglyceride? XD
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yea, the examiners found out halfway through, didn't even notice it lol
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with 5iii) wat i did was write down 3 and 2 assuming two carbon atom on each side 3*2=6 and n+1 therefore 6+1 =7 so septet would that be counted as wrong ?? oh god!!
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For the CH3CH2OH(aq) + CH3CH2COOH(aq) -----> CH3CH2COOCH2CH3(aq) + H2O(l):
Will I lose a mark for that not being all (l). Because I thought that if water was produced, that means that they would be aqueous? I know I'm wrong, but how am I wrong?
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why wasnt it 360mg ? :-\
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why wasnt it 360mg ? :-\
The concentration was 360mg/L, however the question said that each tablet was dissolved in 100mL of water. Therefore it was 360X0.100L, which equals 36mg.
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For the CH3CH2OH(aq) + CH3CH2COOH(aq) -----> CH3CH2COOCH2CH3(aq) + H2O(l):
Will I lose a mark for that not being all (l). Because I thought that if water was produced, that means that they would be aqueous? I know I'm wrong, but how am I wrong?
Oh, because not enough water is produced to form a proper aqueous solution - you'd need a lot of water relative to other compounds to form a real aqueous solution. Anyhow, the water produced is just absorbed by the H2SO4 catalyst (which is an awesome dehydrating agent).
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I put option A for question 5 because technically, it is the hydrogen bonding between -NH and -C=O, not -CO. Is this ambiguity or my not knowing how to read questions?
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I put option A for question 5 because technically, it is the hydrogen bonding between -NH and -C=O, not -CO. Is this ambiguity or my not knowing how to read questions?
CO often implies C=O, like for instance HCOOH --> the CO refers to C=O.
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how do we get consequencial marks in a chemistry exam, because i put down propanol instead of propan-1-ol, and i did the same thing in the flowchart that describes how we could extract pure propyl propanoate, but when i write down the semistructural formulae, i put down propan-1-ol. would i loose alot of marks for this?
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how do we get consequencial marks in a chemistry exam, because i put down propanol instead of propan-1-ol, and i did the same thing in the flowchart that describes how we could extract pure propyl propanoate, but when i write down the semistructural formulae, i put down propan-1-ol. would i loose alot of marks for this?
Probs lose only 1 mark for that.
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Quick question
I've made the dumbest mistake and read that graph wrong and i got 38mg instead of 36 but i showed all my working out so the examiner will realise it was because i read it wrong...
what do you reckon will happen? Will i drop 1 mark or 1/2 mark??? or 2 marks?
Thanks :)
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1
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A+ would probably be 85% onwards. The cut-off tends to increase every year, but it also depends on the difficulty of the exam :)
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Quick question
I've made the dumbest mistake and read that graph wrong and i got 38mg instead of 36 but i showed all my working out so the examiner will realise it was because i read it wrong...
what do you reckon will happen? Will i drop 1 mark or 1/2 mark??? or 2 marks?
Thanks :)
you might not lose any because 36-38 is fairly close
but otherwise 1 mark at most
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for question 4d, could fractional distillation be an appropriate method to use????
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for question 4d, could fractional distillation be an appropriate method to use????
Unfortunately not.
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but couldn't you explain that if another substance separated at a different boiling point to the propanoate from the mixture then this indicates that substance is not pure??
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but couldn't you explain that if another substance separated at a different boiling point to the propanoate from the mixture then this indicates that substance is not pure??
You can't actually tell whether the substances are being separated or not though.
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would i get any marks though ??
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If it was a three mark question I'd give you one mark but since it was only worth two, you probably won't get any, unfortunately.
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The other thing is that fractional distillation will just separate the components of the reaction mixture. You wouldn't know which of the components is the ester.
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ah well too bad for me, I don't know why it didn't come to my mind to put gas chromatography instead of frac distillation :P