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

ray2012

Jaysus I got 138 as well and I was sure I was wrong and thought of changing it..! Glad that other people got the same answer!

Copper_pipe

weirdspider wrote: »

Well if 2 people got the same then it must be right! Unless we are both wrong :P

Us wrong??? NEVER!

ladymacbeth

What about question 1 calculations, part (f)?
I multiplied the answer by 5 as the water sample was titrated to 200cm3. Hope this was the right move lol

weirdspider

Well I was crossing off the questions I got right as we were going along and the only ones I were unsure of the answers were the maths ones. And I'm now presuming they are correct since you guys got them answers too so now I am almost certainly in A1 territory

Laura229

Laura229 wrote: »

What was the reason behing using water as the benzoic solvent?

It is soluble at high temp (removes insoluble impurities such as Carbon) and it is insoluble at low temp (separates it from the soluble impurities)

RML

ladymacbeth wrote: »

What about question 1 calculations, part (f)?
I multiplied the answer by 5 as the water sample was titrated to 200cm3. Hope this was the right move lol

Where is the 5 coming from?

ladymacbeth

Laura229 wrote: »

As in why:)

Laura229 wrote: »

What was the reason behing using water as the benzoic solvent?

I said Cyclohexane.

weirdspider

Right so
Kc-138/139
Fraction of mass left- 1/8
Ppm O2-7.8(meaning the other calculations were correct)
pH-11.18 or something?

Kingkumar

Laura229 wrote: »

What was the reason behing using water as the benzoic solvent?

i said because benzoic acid dissolves in hot water which is important so that we can do filitration and stuff.. and then it's not soluble in cold water so it crystallizes out. i explained it a bit more but thats basically it

Wait guys, what was wrong with the apparatus in q2? I thought it was that one of the nozzles was the wrong way but I just saw a diagram that was an exact replicate of the one on the examination.
Please don't tell me it was a lack of wire gauze/ tripod?

ladymacbeth

Delighted when I saw Dissolved Oxygen question as Question 1! But it was tricky enough :P The paper was good but the questions themselves were actually quite tricky

Kingkumar

Deleted User wrote: »

Wait guys, what was wrong with the apparatus in q2? I thought it was that one of the nozzles was the wrong way but I just saw a diagram that was an exact replicate of the one on the examination.
Please don't tell me it was a lack of wire gauze/ tripod?

the safety tube wasnt pushed into the water..

xJEx

what were the differences between chem and nuclear reactions?

weirdspider

weirdspider wrote: »

Right so
Kc-138/139
Fraction of mass left- 1/8
Ppm O2-7.8(meaning the other calculations were correct)
pH-11.18 or something?

All match my answers
And for q6, it was a negative in the hundreds is all I remember.

weirdspider

Deleted User wrote: »

Wait guys, what was wrong with the apparatus in q2? I thought it was that one of the nozzles was the wrong way but I just saw a diagram that was an exact replicate of the one on the examination.
Please don't tell me it was a lack of wire gauze/ tripod?

I said no steam trap and to remove the heat source to rectify it was unsure of that one!

ladymacbeth

Deleted User wrote: »

Wait guys, what was wrong with the apparatus in q2? I thought it was that one of the nozzles was the wrong way but I just saw a diagram that was an exact replicate of the one on the examination.
Please don't tell me it was a lack of wire gauze/ tripod?

I said the Liebeg Condenser was assembled incorrectly. They never include wire gauze etc in their diagrams anyways

RML

xJEx wrote: »

what were the differences between chem and nuclear reactions?

I talked about the toxic waste produced by nuclear reactions and the expense..

weirdspider

I'd say about 10% of candidates attempted 2 and 6

Kingkumar

Kingkumar wrote: »

the safety tube wasnt pushed into the water..

Damn! In all the diagrams I've ever seen, one nozzle of the liebig condenser points down and one points up. I thought that was the wrong set up.

Prodigious

RML wrote: »

I talked about the toxic waste produced by nuclear reactions and the expense..

chemical reactions do not affect the nucleus

weirdspider

RML wrote: »

I talked about the toxic waste produced by nuclear reactions and the expense..

Huh? I just said changes in nucleus/transmutation in nuclear, not in chemical

0mega

That was soooo nice.

xJEx

RML wrote: »

I talked about the toxic waste produced by nuclear reactions and the expense..

I said that mass can change in nuclear.
And then i said that energy can be converted into mass..
both were kind of similar reasons actually

ladymacbeth

xJEx wrote: »

what were the differences between chem and nuclear reactions?

i said;
Chem - bonds are broken and new bonds are formed, Only involves electrons so the nucleus stays the same
Nuclear - nucleus changes, so a new element is formed

xJEx

xJEx wrote: »

what were the differences between chem and nuclear reactions?

Chem reactions:
1. Involve breaking and forming of bonds
2. Involve electrons

Nuclear
1. Don't involve breaking and forming of bonds
2. Involve the nucleus

RML

Prodigious wrote: »

chemical reactions do not affect the nucleus

weirdspider wrote: »

Huh? I just said changes in nucleus/transmutation in nuclear, not in chemical

Yup yous are right!

weirdspider

Deleted User wrote: »

Damn! In all the diagrams I've ever seen, one nozzle of the liebig condenser points down and one points up. I thought that was the wrong set up.

It was only worth like 6 marks I think

xJEx

Did anyone get 8/3 for the oxidation number of iron in one of the equations?
And was Al the reducing one?

Kingkumar

xJEx wrote: »

Did anyone get 8/3 for the oxidation number of iron in one of the equations?
And was Al the reducing one?

yup was the mass of the aluminium 432g? and aluminium oxide 816?

weirdspider

weirdspider wrote: »

It was only worth like 6 marks I think

I know :P It just seems so simple that it annoys me that I slipped up.

xJEx wrote: »

Did anyone get 8/3 for the oxidation number of iron in one of the equations?
And was Al the reducing one?

Yup

xJEx

Kingkumar wrote: »

yup was the mass of the aluminium 432g? and aluminium oxide 816?

YES

ladymacbeth

Q 11 acid-base 12.05 pH

weirdspider

Deleted User wrote: »

I know :P It just seems so simple that it annoys me that I slipped up.



Yup

No me too like that means straight to an A2 in that question. I finished all 3 experiment questions and the 1st and last went better so hopefully I won't be needing that one!

weirdspider

weirdspider wrote: »

No me too like that means straight to an A2 in that question. I finished all 3 experiment questions and the 1st and last went better so hopefully I won't be needing that one!

Well we have a margin of 40 marks to slip up before we lose our A1. And I literally think I got 50/50 in a lot of those questions!

_LilyRose_

RML wrote: »

For Q6, heat change, did anyone get -412.2?

I did! And I was sure it worked out with the equations....! There's hope!

Kingkumar

Deleted User wrote: »

Well we have a margin of 40 marks to slip up before we lose our A1. And I literally think I got 50/50 in a lot of those questions!

same but i never know with the marking schemes...i hardly make "mistakes" but sometimes i dont say the thing that the marking scheme requires or i don't say enough to get all the marks just worried that stuff like that will add up lol

_LilyRose_

Did anyone at all get 3.76 ppm? Everyone seems to be getting 7.5 or something??

lovelyoner

Deleted User wrote: »

Damn! In all the diagrams I've ever seen, one nozzle of the liebig condenser points down and one points up. I thought that was the wrong set up.

I said the same. It'll probably be accepted; if the upper nozzle doesn't face upwards then bubbles form in the Liebig condenser and you don't get overall, even cooling. The fact that they noted the whole direction of the water thing as well makes me think it'd be okay?

Laura229

Does anyone know why change in pressure had no effect on equilibrium? Was it anything got to do with equilibrium being aqueous?

Copper_pipe

Are there any attempt marks for the titration calculation? I got 15.04 ppm I think?

Hamza Malik

_LilyRose_ wrote: »

Did anyone at all get 3.76 ppm? Everyone seems to be getting 7.5 or something??

I think you forgot to take into account it was in the ratio 2:1

comeclosa

_LilyRose_ wrote: »

I did! And I was sure it worked out with the equations....! There's hope!

I was sure mine worked out with the equations and I got -120 something

this is tense :P

ladymacbeth

_LilyRose_ wrote: »

Did anyone at all get 3.76 ppm? Everyone seems to be getting 7.5 or something??

please tell me you're not talking about question 1 part (f)

football girl

Does anyone know why change in pressure had no effect on equilibrium? Was it anything got to do with equilibrium being aqueous?

Exactly...only holds for gases

ladymacbeth

comeclosa wrote: »

this is tense :P

it really is

Kingkumar

comeclosa wrote: »

I was sure mine worked out with the equations and I got -120 something

this is tense :P

the actual heat of reaction is -127.2 so yeah its somewhere in the -120's

_LilyRose_

Hamza Malik wrote: »

I think you forgot to take into account it was in the ratio 2:1

No because definitely divided my answer for the moles of iodine by 2 to get moles of oxygen....Anyway I probably did something else wrong!

ladymacbeth wrote: »

please tell me you're not talking about question 1 part (f)

Yes sorry!

mrkiscool2

Copper_pipe wrote: »

Are there any attempt marks for the titration calculation? I got 15.04 ppm I think?

Yeah there is, the correct answer is only worth a certain amount of the marks, as long as you can show you know the equation and how it works you get marks for it!

Also, if anyone is thinking of doing Science in Uni, ye did the best subject. People seem to have the hardest time grasping Chem, so congrats lads. Chemistry isn't an easy subject for the LC!

Hamza Malik

For rates of reaction people are getting -130 or -412 so.. which one is it?

weirdspider

Deleted User wrote: »

Well we have a margin of 40 marks to slip up before we lose our A1. And I literally think I got 50/50 in a lot of those questions!

Wooo congrats