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Author Topic: SUGGESTED ANSWERS!!!  (Read 40896 times)

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Tonychet2

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SUGGESTED ANSWERS!!!
« on: June 13, 2012, 03:25:15 pm »
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


« Last Edit: June 14, 2012, 02:29:57 pm by Tonychet2 »

Tonychet2

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Re: SUGGESTED ANSWERS!!!
« Reply #1 on: June 13, 2012, 03:35:36 pm »
any questions feel free to ask note i may be wrong..
n please correct me if im wrong lol

ligands

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Re: SUGGESTED ANSWERS!!!
« Reply #2 on: June 13, 2012, 03:37:56 pm »
with 3b wouldn't it be amino and carboxyl because it asks for the function groups?

Nobby

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Re: SUGGESTED ANSWERS!!!
« Reply #3 on: June 13, 2012, 03:38:52 pm »
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?

Tonychet2

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Re: SUGGESTED ANSWERS!!!
« Reply #4 on: June 13, 2012, 03:40:03 pm »
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

thushan

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Re: SUGGESTED ANSWERS!!!
« Reply #5 on: June 13, 2012, 03:41:02 pm »
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 :/
« Last Edit: June 13, 2012, 03:50:41 pm by thushan »
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sahil26

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Re: SUGGESTED ANSWERS!!!
« Reply #6 on: June 13, 2012, 03:41:09 pm »
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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Tonychet2

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Re: SUGGESTED ANSWERS!!!
« Reply #7 on: June 13, 2012, 03:41:26 pm »
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

thushan

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Re: SUGGESTED ANSWERS!!!
« Reply #8 on: June 13, 2012, 03:42:55 pm »
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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Tonychet2

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Re: SUGGESTED ANSWERS!!!
« Reply #9 on: June 13, 2012, 03:43:14 pm »
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

joseph95

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Re: SUGGESTED ANSWERS!!!
« Reply #10 on: June 13, 2012, 03:45:20 pm »
SAQ6ii - i got 360 mg not 36...

It's 360mg in 1L. It's asking for how much in 100ml, so it's 36mg.

thushan

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Re: SUGGESTED ANSWERS!!!
« Reply #11 on: June 13, 2012, 03:47:00 pm »
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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Tonychet2

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Re: SUGGESTED ANSWERS!!!
« Reply #12 on: June 13, 2012, 03:48:10 pm »
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

jadams

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Re: SUGGESTED ANSWERS!!!
« Reply #13 on: June 13, 2012, 03:48:23 pm »
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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vnguyenprochemist

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Re: SUGGESTED ANSWERS!!!
« Reply #14 on: June 13, 2012, 03:48:46 pm »
Isn't NaCl aqueous?
EDIT: Could you write OH-(aq) + H+(aq) => H2O(l) for the neutralisation?