2014 Chemistry Exam Solutions

[Jnf17]

Thanks for your corrections guys and I've actually been secretly editing the answers for the past 10 minutes.

15 is C, 21 is C, 30 is B

I believe 16 is C though since I don't think you can extrapolate (you can but its not the MOST accurate)

I think that anything below the data points that you have got can be extrapolated as a linear region. However above the highest data value it cannot be used as the graph cannot be necessarily be assumed to be linear. That is how I have interpreted it anyway. Will see how Thushan and VCAA see it

Thanks for the solutions though!

[acinod]

I have read that accuracy is maintained when you extrapolate down.

I think you are correct in that we can extrapolate down: http://en.wikipedia.org/wiki/Standard_addition

So 16 is B (for now I guess)

[thushan]

SAQ 1a.

Two energy profiles; uncatalysed rising to 335, dropping to 92.4 and tungsten uncatalysed rising to 162, dropping to 92.4.

SAQ 1b.

Tungsten; lower activation energy required means a greater fraction of collisions between ammonia molecules will be successful, and hence there is a higher frequency of successful collisions between ammonia molecules, and thereby a greater rate of decomposition.

SAQ 2a.

A - CH2CH2, C - CH2=CH-CH3, D - CH3COOH, E - CH3CH2OH

SAQ 2b.

B - propan-1-amine, D - ethanoic acid

SAQ 2c.

CH3COOCH2CH2CH3, propyl ethanoate
SEMI STRUCTURAL FORMULA NEEDED HERE.

SAQ 3a.

total energy from ethanol = 1.80/46.0 x 1364 = 53.3 kJ
energy absorbed by water = 100.0 x 4.18 x 15.0 = 6270 J = 6.27 kJ
% lost = 88.3%

SAQ 3b.

- insulate metal container
- insulate spirit burner
- close metal container

Lots of things here.

SAQ 3ci.

CH3(CH2)12 COOCH3 - ester

SAQ 3cii.
Canola oil and biodiesel are mixtures of different compounds with different molar masses, it is hence impossible to calculate the total amount of molecules in either, given the mass of these mixtures.

SAQ 4a.
Two of the following:
- OH (acid) at ~3000
- CH at ~3000
- C=O at ~1700

SAQ 4b.
x = 3, y = 5

Mass spectrum shows two molecular ions at 108 and 110. Take away 35-Cl and the two Os from mass = 108, you get remaining mass 108-35-32=41, which is consistent with a C3H5 group.

SAQ 4ci.

Either of:
- presence of CH3 and a CHCl group
- Cl atom on carbon-2

SAQ 4cii.
CH3CHClCOOH

SAQ 4d.
Cl has 2 isotopes which are present in significant amounts. m/z = 108 is C3H5O2³⁵Cl and m/z = 110 C3H5O2³⁷Cl.

SAQ 5a.
HO-CH2-COOH

SAQ 5b.
Increase; adding glycolate push equilibrium to left, consuming H3O+, decrease [H3O+].

SAQ 5c.
13 mol L-1

SAQ 5d.
n(glycolate) = 1.3 mol
n(Na2CO3) = 1.3/2 = 0.66 mol (using calc values)
m(Na2CO3) = 70 g

SAQ 5e.
- safety goggles
- gas mask
- ventilation
- protective gloves

Any of these hehe

SAQ 6ai.

K = [HI]^2/[H2][I2]

SAQ 6aii.

Rice table!

Reactant Initial Change Equilibrium
H2 2.00   -1.93   0.07
I2 3.00    -1.93   1.07
HI 0        +3.86  3.86

Concentrations same as amounts since 1 L vessel.
K = 2 x 10^2

SAQ 6bi.
Self explanatory

SAQ 6bii.
Same thing, but quicker (no change in equilibrium position)

SAQ 7a.
non polar: any of glycine, alaine, valine, leucine, isoleucine
acid: glutamic acid or aspartic acid

SAQ 7bi.
cysteine

SAQ 7bii.
serine, asparagine

SAQ 7biii.
lysine

SAQ 7biv.
dispersion forces/Van der Waal's forces

SAQ 7c.
- low pH disturbs ionic interactions between COO- and NH3+
- alters tertiary structure therefore shape of active site of trypsin
- trypsin therefore unable to bind to its substrates

SAQ 8a.
oxidation

Not accepting redox, since only the oxidation half equation is shown here.

SAQ 8bi.
m(BaSO4) = 0.474 g
n(BaSO4) = 0.00203 mol
n(SO2) = 0.00203 mol
m(SO2) = 0.130 g
ans = 0.260%

SAQ 8bii.
2.60 x 10^3 ppm

SAQ 8biii.
Ensure all of SO2, even SO2 on the inside of the dried apricot, reacts with the H2O2.

SAQ 8ci.
1:1

SAQ 8cii.
m(I2) = 4.95/500.0 x15.0 = 0.149 g
n(I2) = 5.85 x 10^-4 mol
n(H2O) = 5.85 x 10^-4 mol
m(H2O) = 0.0105 g

SAQ 8ciii.

0.115%

SAQ 9a.

Mg2+ (l) + 2e- -> Mg (l)
2Cl- (l) -> Cl2 (g) + 2e-

SAQ 9b.
Prevent Mg contacting and reacting vigorously with O2.

SAQ 9c.
Zn2+ better oxidant than Mg2+, will be discharged in preference at cathode.

SAQ 9d.
Fe stronger reductant than Cl-, will corrode as anode: Fe (s) --> Fe2+ (l) + 2e-. Even Fe2+ is a better reductant than Cl-, so you can even get Fe2+ (l) --> Fe3+ (l) + e-

At cathode, since you have a mixture of Fe2+, Fe3+ and Mg2+, the former two are better oxidants, so Fe will be discharged at cathode:

Fe3+ + e- --> Fe2+
Fe2+ + 2e- --> Fe

SAQ 10a.

Zn(s) + 2OH- (aq) --> Zn(OH)2 + 2e-

SAQ 10b.
Not sure what VCAA wants. I can think of the following:
- ensure an alkaline environment (for some reason this sounds a little superficial... :/ )
- precipitate out Zn2+ ions to ensure products are solid and don't leak out

SAQ 10c.
Q = It = 0.00236 x 10 x 60 x 60 = 85 C
n(e-) = 85/96500 = 8.8 x 10^-4 mol
n(Zn) = n(e-)/2 = 4.4 x 10^-4 mol
m(Zn) = 65.4 x n(Zn) = 0.029 g

SAQ 10d.
H2 (g) + 2 OH- (aq) --> 2H2O (l)

SAQ 11a.
+ Br2 (l) + 2H+ (aq) + 2e- --> 2HBr (aq)
- QH2(aq) --> Q (aq) + 2H+ (aq) + 2e-

SAQ 11b.
Q (aq) + 2 HBr (aq) --> QH2 (aq) + Br2 (l)

SAQ 11ci.
LEFT

SAQ 11cii.
Ensure QH2 and Br2 do not react directly. If they do, heat produced that could have been converted to electrical energy. Reduced efficiency.

SAQ 11d.
2H2O (l) --> 2H2 (g) + O2 (g)

SAQ 11e.
QH2 (aq)+ H2O(l) --> QH- (aq) + H3O+(aq)
K = [H3O+][QH-]/[QH2]

SAQ 11f.
The quinone can be continuously produced at a rate similar to consumption - by constantly growing crops of rhubarb.

[Jnf17]

One question I did not understand was 23. B is the energy that methane would give out at SLC. However there is the component to the question where H2O is involved. In other VCAA exams and in chapter questions - when water is in a molecule, the energy release is less as energy is consumed evaporating the water. (Brown coal on the 2013 exam for example where wet coal releases less energy than dry coal). With this reasoning, I would have thought 23 was A as it was slightly less that answer B. Don't know what others thought?

[SeanC]

Can 3ci not also be a carboxylic acid?

[S61778]

Can 3ci not also be a carboxylic acid?

I did that too, but I think biodiesel molecule means ester

[Brunette15]

What are everyone's thoughts for the A+ cut off this year??

[Jnf17]

What are everyone's thoughts for the A+ cut off this year??

I am in no way an expert at all but I thought it was harder than last years which was 85% So I would guess personally 80-83%

[d4m0]

One question I did not understand was 23. B is the energy that methane would give out at SLC. However there is the component to the question where H2O is involved. In other VCAA exams and in chapter questions - when water is in a molecule, the energy release is less as energy is consumed evaporating the water. (Brown coal on the 2013 exam for example where wet coal releases less energy than dry coal). With this reasoning, I would have thought 23 was A as it was slightly less that answer B. Don't know what others thought?

You're right but the wording of the question is why it's B. It asks for 'The amount of energy released by the complete combustion of methane extracted from a 1kg sample of methane hydrate...'. The methane extraction energy cost is ignored because all it's asking is about the energy from the methane after it was extracted.

[Nguyensanity]

Agh, wasn't consistent with my sig figs. Really hope I'm not caught out on the question they decide to scrutinise. :/

[Chalkhous]

For Question 7biii I wrote lysine,and aspartic acid. Would that be fine?

[Edward Elric]

SAQ 1a.

Two energy profiles; uncatalysed rising to 335, dropping to 92.4 and tungsten uncatalysed rising to 162, dropping to 92.4.

SAQ 1b.

Tungsten; lower activation energy required means a greater fraction of collisions between ammonia molecules will be successful, and hence there is a higher frequency of successful collisions between ammonia molecules, and thereby a greater rate of decomposition.

SAQ 2a.

A - CH2CH2, C - CH2=CH-CH3, D - CH3COOH, E - CH3CH2OH

SAQ 2b.

B - propan-1-amine, D - ethanoic acid

SAQ 2c.

CH3COOCH2CH2CH3, propyl ethanoate
SEMI STRUCTURAL FORMULA NEEDED HERE.

SAQ 3a.

total energy from ethanol = 1.80/46.0 x 1364 = 53.3 kJ
energy absorbed by water = 100.0 x 4.18 x 15.0 = 6270 J = 6.27 kJ
% lost = 88.3%

SAQ 3b.

- insulate metal container
- insulate spirit burner
- close metal container

Lots of things here.

SAQ 3ci.

CH3(CH2)12 COOCH3 - ester

SAQ 3cii.
Canola oil and biodiesel are mixtures of different compounds with different molar masses, it is hence impossible to calculate the total amount of molecules in either, given the mass of these mixtures.

SAQ 4a.
Two of the following:
- OH (acid) at ~3000
- CH at ~3000
- C=O at ~1700

SAQ 4b.
x = 3, y = 5

Mass spectrum shows two molecular ions at 108 and 110. Take away 35-Cl and the two Os from mass = 108, you get remaining mass 108-35-32=41, which is consistent with a C3H5 group.

SAQ 4ci.

Either of:
- presence of CH3 and a CHCl group
- Cl atom on carbon-2

SAQ 4cii.
CH3CHClCOOH

SAQ 4d.
Cl has 2 isotopes which are present in significant amounts. m/z = 108 is C3H5O2³⁵Cl and m/z = 110 C3H5O2³⁷Cl.

SAQ 5a.
HO-CH2-COOH

SAQ 5b.
Increase; adding glycolate push equilibrium to left, consuming H3O+, decrease [H3O+].

SAQ 5c.
13 mol L-1

SAQ 5d.
n(glycolate) = 1.3 mol
n(Na2CO3) = 1.3/2 = 0.66 mol (using calc values)
m(Na2CO3) = 70 g

SAQ 5e.
- safety goggles
- gas mask
- ventilation
- protective gloves

Any of these hehe

SAQ 6ai.

K = [HI]^2/[H2][I2]

SAQ 6aii.

Rice table!

Reactant Initial Change Equilibrium
H2 2.00   -1.93   0.07
I2 3.00    -1.93   1.07
HI 0        +3.86  3.86

Concentrations same as amounts since 1 L vessel.
K = 2 x 10^2

SAQ 6bi.
Self explanatory

SAQ 6bii.
Same thing, but quicker (no change in equilibrium position)

SAQ 7a.
non polar: any of glycine, alaine, valine, leucine, isoleucine
acid: glutamic acid or aspartic acid

SAQ 7bi.
cysteine

SAQ 7bii.
serine, asparagine

SAQ 7biii.
lysine

SAQ 7biv.
dispersion forces/Van der Waal's forces

SAQ 7c.
- low pH disturbs ionic interactions between COO- and NH3+
- alters tertiary structure therefore shape of active site of trypsin
- trypsin therefore unable to bind to its substrates

SAQ 8a.
oxidation

Not accepting redox, since only the oxidation half equation is shown here.

SAQ 8bi.
m(BaSO4) = 0.474 g
n(BaSO4) = 0.00203 mol
n(SO2) = 0.00203 mol
m(SO2) = 0.130 g
ans = 0.260%

SAQ 8bii.
2.60 x 10^3 ppm

SAQ 8biii.
Ensure all of SO2, even SO2 on the inside of the dried apricot, reacts with the H2O2.

SAQ 8ci.
1:1

SAQ 8cii.
m(I2) = 4.95/500.0 x15.0 = 0.149 g
n(I2) = 5.85 x 10^-4 mol
n(H2O) = 5.85 x 10^-4 mol
m(H2O) = 0.0105 g

SAQ 8ciii.

0.115%

SAQ 9a.

Mg2+ (l) + 2e- -> Mg (l)
2Cl- (l) -> Cl2 (g) + 2e-

SAQ 9b.
Prevent Mg contacting and reacting vigorously with O2.

SAQ 9c.
Zn2+ better oxidant than Mg2+, will be discharged in preference at cathode.

SAQ 9d.
Fe stronger reductant than Cl-, will corrode as anode: Fe (s) --> Fe2+ (l) + 2e-. Even Fe2+ is a better reductant than Cl-, so you can even get Fe2+ (l) --> Fe3+ (l) + e-

At cathode, since you have a mixture of Fe2+, Fe3+ and Mg2+, the former two are better oxidants, so Fe will be discharged at cathode:

Fe3+ + e- --> Fe2+
Fe2+ + 2e- --> Fe

8a. Wow really, surely theyll also accept redox reaction?

[Chalkhous]

For 11D doesnt adding the two h20 equations give you 2h20->h2+O2+2Hpositive?

[apreslapluie]

are there no electrons in 10d's equation? 

[Blondie21]

8a. Wow really, surely theyll also accept redox reaction?

Idk man cause the oxidation reaction is given?