how was it (1 Viewer)

[Titburger]

Easy test. What was so hard about the galvanic cell? The Fe3+ reduced to Fe2+ +e- and the Fe2+ reduced to Fe +2 e- and the Pb was oxidised and then you just used the standard potentials.

 

[moke]

does anyone have a copy of the multiple choice questions? I left mine in the exam room
also, did people get for the galvanic cell one that Fe3+ reduced to Fe2+? and that bloody shipwrecks question on silver plating the nickel spoon. I had the spoon the cathode and a graphite anode in a silver nitrate solution. But would it work seeing the water has a higher electrode potential?

 

[we0426]

I think I got 15 B, and 1.78% nitrogen, 0.9 grams for the ethanol combustion, anyone else?

yep 0.9g for ethanol

i think ppl have calculated it wrong coz they got answers like 550g i was like wtfffffffffffffffffffffffff..lol

 

[FlameFromBeyond]

i got 15 B but i dont know why, 1.8% nitrogen because it was 2s.f. i think... and if not i got like 1.77%.

your ethanol is incorrect though, sorry dude

Ethanol mass was around 3.58g or something like that...

 

[mitchwong650]

does anyone have a copy of the multiple choice questions? I left mine in the exam room
also, did people get for the galvanic cell one that Fe3+ reduced to Fe2+? and that bloody shipwrecks question on silver plating the nickel spoon. I had the spoon the cathode and a graphite anode in a silver nitrate solution. But would it work seeing the water has a higher electrode potential?

silver ions have a higher reduction potential than water

 

[FlameFromBeyond]

that bloody shipwrecks question on silver plating the nickel spoon. I had the spoon the cathode and a graphite anode in a silver nitrate solution. But would it work seeing the water has a higher electrode potential?

I made the spoon the cathode in an AgNO3 solution, with an inert platinum anode. Silver deposited on cathode, voila - silver plating!

 

[buildabridge]

I got: 1.78% nitrogen, 3.51g for ethanol and 0.9V for the cell.
I thought it was different to past exams. A bit tricky in places but overall ok I guess. We can only wait and see I suppose.

 

[sam5]

does anyone have a copy of the multiple choice questions? I left mine in the exam room
also, did people get for the galvanic cell one that Fe3+ reduced to Fe2+? and that bloody shipwrecks question on silver plating the nickel spoon. I had the spoon the cathode and a graphite anode in a silver nitrate solution. But would it work seeing the water has a higher electrode potential?

im the same. NOBODY WILL POST IT UP.

i put 3 half equations (fucking hell) and put nickel spoon as anode (fuck).

Can anyone write up heat of combustion question plz?

 

[mitchwong650]

yep 0.9g for ethanol

i think ppl have calculated it wrong coz they got answers like 550g i was like wtfffffffffffffffffffffffff..lol

i don't know how you did it...
but,

/\H = -mc/\t

where m was 210, c is 4.18, t was 65

/\H = 57.057 KJ/g

turn this into /mol

57.057 x mm(ethanol) / m(ethanol) = 1376/2 (50% heat lost to environment)

rearrange to find m(ethanol)

m(ethanol) = 2624.622/688

=3.8 grams (2 sf)

 

[FlameFromBeyond]

i don't know how you did it...
but,

/\H = -mc/\t

where m was 210, c is 4.18, t was 65

/\H = 57.057 KJ/g

turn this into /mol

57.057 x mm(ethanol) / m(ethanol) = 1376/2 (50% heat lost to environment)

rearrange to find m(ethanol)

m(ethanol) = 2624.622/688

=3.8 grams (2 sf)

+1

pretty much what i did... i worked out q=mc/\T, multiplied that by two, (in kJ), worked from molar heat of combustion, found how many moles needed, from that found mass

 

[about7]

mannn........... fail....:mad1:

 

[H4rdc0r3]

If i got 1.78% because i rounded off the number of moles in the previous question do i still get full marks?

 

[hughesie767]

Hey do you guys see any problems with my MC answers?
1. C
2. C
3. D
4. C
5. A
6. D
7. B
8. A
9. C
10. B
11. D
12. A
13. B
14. B
15. A

I got 1.77% for the nitrogen content, 3.8 something grams for the ethanol and 0.9 V for the galvanic cell

i got exactly what u got. 15 i got A. is this logic correct. 25C = 8mg/L therefore 80mg in 10L = 0.08g in 10L. n=0.08/32 = 0.0025mols then x by 24.79 = 0.061975L = 61.975ml = 62.0

 

[mitchwong650]

If i got 1.78% because i rounded off the number of moles in the previous question do i still get full marks?

you should never ever round.

you probably won't get full marks.

and also, it may have been 2s.f. not 3 (i dont remember though)

 

[Twickel]

He guys with the Nitro calc I got 1.45% only because I rounded off everything, I showed all working do i still get the full mark I was ccnsistant 3dp for every thing

 

[decapitated]

I swear they said heat of combustion was 1367 kj/mol. I have to get my eyes checked- ended up with 4.1g

 

[mitchwong650]

He guys with the Nitro calc I got 1.45% only because I rounded off everything, I showed all working do i still get the full mark I was ccnsistant 3dp for every thing

no, you're not meant to round until you get to your final answer, where you put it in the correct amount of sig figs.

I swear they said heat of combustion was 1367 kj/mol. I have to get my eyes checked- ended up with 4.1g

perhaps, as it said 50% is lost to the environment.

keep reading the question buddy, don't cut corners

 

[danal353]

I thought that it could've been worser, seriously. I was shitting myself before the exam and found that the questions were all answerable and I'm glad that its over and my 2 days cramming should pay off. I reckon that I'll get somewhere between High 70's low 80's.

As for that NH3 question, I forgot to convert it into percentage >< But yeah, I got around 2.2%

Couldn't do Q14 for Multiple choice, so just guessed that >_<

Also, the one with the titration graphs was alright, I put CH3COO- for the conjugate base, although now thinking about it, that's probably one.

And for whoever it was who wanted to know, I put NH3 + HCl --> NH4Cl for the bread question.

haha same - I had two days of cramming after ext eng and I was so stressed last night - glad it wasn't as bad as I thought..

I did question 14 in the last five minutes, after I had finished everything else - had an epiphany...

 

[spirky]

dunno if any of you guys are correct with the ethanol if we are talking about the one where you raised the temp of about 200g of water by 65 degrees.. because it would take a rediculous amount of ethanol to heat water that much and they also lost half the heat to the surrounds which means ^H = 2mc^T... so im certain it would be a very large amount
i got 2.2% for the nitrogen in bread...

 

[charlen]

I got: 1.78% nitrogen, 3.51g for ethanol and 0.9V for the cell.
I thought it was different to past exams. A bit tricky in places but overall ok I guess. We can only wait and see I suppose.

pretty sure thats right, prob 95%ish