2013 LC Chemistry Before/After

Laura229 · 18-06-2013 05:15PM

Surely that alone wasnt worth 9 marks though?

lizardspock · 18-06-2013 05:19PM

There was a pretty bad reaction to the paper from my class, although I thought it was fair enough to be honest. Really hoping I've done enough to secure the A1... Did 10 questions but just kinda found there was a part to most questions which could have the potential to be a bit vague in the marking scheme or parts with just a general sting in them!

fingers crossed!

comeclosa · 18-06-2013 05:24PM

Corrosive for the hazard, yes? :P

SecondMan · 18-06-2013 05:26PM

comeclosa wrote: »

Corrosive for the hazard, yes? :P

Yes. I drew a hand that resembled a side-view of a rabbit's head.

Hamza Malik · 18-06-2013 05:27PM

comeclosa wrote: »

Corrosive for the hazard, yes? :P

Yeah I drew the picture of the test tube leaking on to a hand with a dead fish in the background

ladymacbeth · 18-06-2013 05:27PM

IMG_0671.JPG

Already hitting me that I was wrong.

18-06-2013 05:30PM

ladymacbeth wrote: »

IMG_0671.JPG

Already hitting me that I was wrong.

Is n1 not = 2 and n2 = 1??

_LilyRose_ · 18-06-2013 05:30PM

ladymacbeth wrote: »

IMG_0671.JPG

Already hitting me that I was wrong.

But isn't the ratio of the iodine to thiosulfate 1:4?

ladymacbeth · 18-06-2013 05:32PM

Deleted User wrote: »

Is n1 not = 2 and n2 = 1??

:eek:

FUUUUUU*****

Ok. Lesson learned. This is what happens when everything depends on this subject and you're stress levels are at an all time high. This is what happens when you don't read a question properly.

I will remain calm and not shred my exam paper into pieces in frustration. :mad:

18-06-2013 05:32PM

_LilyRose_ wrote: »

But isn't the ratio of the iodine to thiosulfate 1:4?

Nope.
Iodine to Thiosulfate
1 : 2

Oxygen to Iodine
1 : 2

Therefore
Oxygen to Thiosulfate
1 : 4

_LilyRose_ · 18-06-2013 05:34PM

Deleted User wrote: »

Nope.
Iodine to Thiosulfate
1 : 2

Oxygen to Iodine
1 : 2

Therefore
Oxygen to Thiosulfate
1 : 4

Ah yes.

F************

Laura229 · 18-06-2013 05:34PM

For the ammonia reaction was it wrong to say high pressure and low temperature?

ladymacbeth · 18-06-2013 05:35PM

_LilyRose_ wrote: »

Ah yes.

F************

hahahaha i'm not alone.
I'm literally so angry I'm laughing it off.
hahahaha... wtf???!!

_LilyRose_ · 18-06-2013 05:38PM

ladymacbeth wrote: »

hahahaha i'm not alone.
I'm literally so angry I'm laughing it off.
hahahaha... wtf???!!

When I looked at my book like two minutes before the exam I had 1:4 highlighted for the winkler calculations I'm soooooo annoyed at myself now lololololol!

18-06-2013 05:38PM

Laura229 wrote: »

For the ammonia reaction was it wrong to say high pressure and low temperature?

Which question was this?

xJEx · 18-06-2013 05:39PM

Laura229 wrote: »

For the ammonia reaction was it wrong to say high pressure and low temperature?

I was gonna do that but then I figured it wasnt that since it was a rates not equil. Q ... pus a low temperature increases yield of ammonia but actualy slows down the rate

i said increased concentrations and temperature

xJEx · 18-06-2013 05:40PM

What answers did people get for Q3? I got .075 moles, then 4.347 for heat change and 57.96 for heat of reaction

ladymacbeth · 18-06-2013 05:40PM

_LilyRose_ wrote: »

When I looked at my book like two minutes before the exam I had 1:4 highlighted for the winkler calculations I'm soooooo annoyed at myself now lololololol!

So should it have been 1:4?
Or 2:1 as was suggested in the equation?

_LilyRose_ · 18-06-2013 05:42PM

ladymacbeth wrote: »

So should it have been 1:4?
Or 2:1 as was suggested in the equation?

I honestly have no idea! Most people here and that I talked to got different to me but I suppose we'll have to wait to view the papers if we have to haha!

18-06-2013 05:43PM

ladymacbeth wrote: »

So should it have been 1:4?
Or 2:1 as was suggested in the equation?

I worked with 2:1 for the calculation as we needed the concentration of iodine for the question

Then it asked to work with O2 so I halved the molarity of the iodine. (as 2 moles are liberated for every 1 mole O2)
And then used this figure for the rest of the calculations

Glee_GG · 18-06-2013 05:44PM

Kingkumar wrote: »

the safety tube wasnt pushed into the water..

Gas I said "the flask appear to be hovering mid-air so you should put a tripod and gauze underneath" :L Its still true though even if I know they would have used it, they didn't put it in the picture!

SecondMan · 18-06-2013 05:45PM

xJEx wrote: »

I was gonna do that but then I figured it wasnt that since it was a rates not equil. Q ... pus a low temperature increases yield of ammonia but actualy slows down the rate

i said increased concentrations and temperature

Increased pressure would work too as it would cause an increase in collisions.

Kingkumar · 18-06-2013 05:48PM

Glee_GG wrote: »

Gas I said "the flask appear to be hovering mid-air so you should put a tripod and gauze underneath" :L Its still true though even if I know they would have used it, they didn't put it in the picture!

hahaha i was going to put that as well

xJEx · 18-06-2013 05:49PM

SecondMan wrote: »

Increased pressure would work too as it would cause an increase in collisions.

Yeah but low temperature wouldn't. It's kind of a messed up question cause temperature would speed it up but it would decrease the yield of ammonia and theyre asking how to speed up the reaction of ''the production of ammonia''

18-06-2013 05:51PM

xJEx wrote: »

Yeah but low temperature wouldn't. It's kind of a messed up question cause temperature would speed it up but it would decrease the yield of ammonia and theyre asking how to speed up the reaction of ''the production of ammonia''

For production of Ammonia.
By Le Chatalier, the ideal conditions are high pressure and low temperature.
High pressures are expensive to maintain and increase risk of explosion. A compromise pressure of 200 atmospheres is used.
For temperature; if it was too low, the reaction would be too slow and actually slow down production. A compromise temperature of 500 degrees celsius is used.

xJEx · 18-06-2013 05:55PM

Deleted User wrote: »

For production of Ammonia.
By Le Chatalier, the ideal conditions are high pressure and low temperature.
High pressures are expensive to maintain and increase risk of explosion. A compromise pressure of 200 atmospheres is used.
For temperature; if it was too low, the reaction would be too slow and actually slow down production. A compromise temperature of 500 degrees celsius is used.

Yeah I know but it was a rates question not a equilibrium

18-06-2013 05:58PM

xJEx wrote: »

Yeah I know but it was a rates question not a equilibrium

Sorry I just saw someone mention ammonia production.

For what speeds up rate of reaction.

1. Nature of reactants (are they both ionic or covalent) didn't apply to question
2. Temperature of reaction
3. Concentration of reactants
4. Particle size didn't apply
5. Presence of a catalyst

0mega · 18-06-2013 05:59PM

xJEx wrote: »

What answers did people get for Q3? I got .075 moles, then 4.347 for heat change and 57.96 for heat of reaction

Same here but should it have been -57.96 for heat of reaction as it was exothermic and produced heat?

Jackobyte · 18-06-2013 06:00PM

Glee_GG wrote: »

Gas I said "the flask appear to be hovering mid-air so you should put a tripod and gauze underneath" :L Its still true though even if I know they would have used it, they didn't put it in the picture!

I said they had no water in with their cloves. :P The diagram definitely had more than one flaw so they'll have to be generous with the marking scheme on it.

18-06-2013 06:01PM

0mega wrote: »

Same here but should it have been -57.96 for heat of reaction as it was exothermic and produced heat?

Can I ask how you got the heat change? I had never done a question where the two initial temps were different so I added them both and divided by 2 but I'm guessing that was wrong?

***2013 LC Chemistry Before/After***

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2013 LC Chemistry Before/After