Thoughts? (1 Viewer)

[danz90]

Sweet i got that. And yeah i said it wasnt, because k was out be a d.p or something is that what you got?

The equilibrium constant for that reaction was 26, and then when I determined the K-constant with the quantities they provided (because it was in moles, you had to divide by the 5.00L of gas for each gas, to get concentration) and found K (for those quantities) to be like 16.23...

So I said therefore not in equilibrium at these quantities, because the constant calculated does not equal theortical K-constant for when the system is at equilibrium.

 

[Aaron.Judd]

These are some calculation answers that I got, that I can remember. Can someone compare/clarfiy?

The average mass of zinc in tablets - 0.16mg

Titration question, [HCl] = 1.057 mol/L

The identitfy of gas = H₂(g)

Highest energy released by: Hydrogen gas fuel

Amount of energy released by 80L petrol = 2.6 x 10⁶ kJ , or something like 2,640,000 kJ.

Litres of Hydrogen Gas required: something like 269,xxx L ?

I got the same for the identity of the gas, the 80L of petrol and the H2 gas required calculations. Can't remember for the titration and I'm pretty sure I screwed the zinc tablet question, although thankfully it as only worth 2 marks.

 

[Aaron.Judd]

Voltage of galvanic cell -- 1.60V

I got this as well.

 

[r0kstar]

because the concentration was 1.6mg/L

And the sample was 100mL, you had to multiply 1.6 by 0.100L to get 0.16mg

oh damn!
oh well
thanks!

 

[Aaron.Judd]

For people doing industrial, did you determine that the system was NOT at equilibrium?

I said it wasn't at equilibrium. At first i did, then I realized I'd fucked teh calculation so I fixed it and realized it wasn't at equilibrium (didn't think it was either by looking at the equation).

 

[Aaron.Judd]

i did that too and got 1.6mg zinc.... does any1 no how to get the answer?

You then had to do a couple of calculations with it, although I think I screwed them.

 

[independantz]

I got this as well.

Same.

 

[Aaron.Judd]

yeh i got the exact same results. What a relief.
What did everyone get for the 4th mc question? Was it water or nitrogen that is most abundant in the atmosphere at the ground state?

Defiantly nitrogen.

 

[r0kstar]

wat equations did evry1 put for the ethanol one?
love

 

[danz90]

Yeah, actually the one I wrote up before ( the galvanic cell equation) was a typo.. the Cl- are on the right, because the chlorine gas is reduced.

 

[cookiemonsterz]

does any 1 think they will take sig-figs into account for any of the questions, i used them for all of them accept the ones about fuels. Thought it was stupid to do 3 sig figs on like a 10 digit number

 

[danz90]

wat equations did evry1 put for the ethanol one?
love

Acid hydrolysis of cellulose
Fermentation of glucose to produce ethanol
Combustion of Ethanol

 

[danz90]

does any 1 think they will take sig-figs into account for any of the questions, i used them for all of them accept the ones about fuels. Thought it was stupid to do 3 sig figs on like a 10 digit number

Well with the one for fuels, you should use scientific notation.

Like, for the energy released by petrol, I put

2.6 x 10⁶ kJ (2.s.f.)

 

[pissedoff]

for the zinc question they asked for mass

aas 1.6 was the concentration and c = n/v therefore mols = 0.16

mass = mol * fw

so its actually 0.16 * molar mass of zinc

as for the hydrogen question its somewhere around 3 billion with 28 litres of hydrogen gas needed to produce the same effect.

also for the ethanol one

it was vital to show that 6 mols of carbon dioxide were used in the photosynthesis raction before showing 6 mols were released

 

[danz90]

for the zinc question they asked for mass

aas 1.6 was the concentration and c = n/v therefore mols = 0.16

mass = mol * fw

so its actually 0.16 * molar mass of zinc

as for the hydrogen question its somewhere around 3 billion with 28 litres of hydrogen gas needed to produce the same effect.

also for the ethanol one

it was vital to show that 6 mols of carbon dioxide were used in the photosynthesis raction before showing 6 mols were released

the concentration was in mg/L , not mol/L

 

[cathyjun28]

Overall, it was a good exam. I agree with too many calculation questions and I screwed up the galvanic cell one. Anyone did forensic chemistry, I was really hoping they won't test reducing and non-reducing sugars, but they tested that. And for that 7 marks question on emission spectrum, I'm not very confident with my answers.

 

[fishbulb]

Acid hydrolysis of cellulose
Fermentation of glucose to produce ethanol
Combustion of Ethanol

hmm, it said critically evaluate the statement. That seems like you just discussed how to produce it.

 

[sparkerasp]

I thought it was a pretty good exam. I would have preferred it if they put something on batteries, radioisotopes and the Solvay process thought.

 

[JamesTockuss]

hmm, it said critically evaluate the statement. That seems like you just discussed how to produce it.

I agree. I think the question was more looking at the fact that Ethanol is not in fact carbon neutral, as you need to expend so much energy when you are producing ethanol from cellulose. And then I guess you had to talk about whether or not it was good for fighting against global warming - which it is, because unlike petrol the CO2 that it expels it absorbed by plants, which are used to make ethanol - wheras petrol is from petroleum - and thus it minimises global warming

 

[danz90]

hmm, it said critically evaluate the statement. That seems like you just discussed how to produce it.

Nah I did critically evaluate it. If you look at critically evaluate keywords on BOS Site, you need to look deeply at the issues/processes involved, to make a more comprehensive judgement.
Thats the difference between evaluate and then critically evaluate, I think.

Meh, even with 4/5 for that one I'd be happy.