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

simons545

Hamza Malik wrote: »

yeah I will. I didn't use them here cause its hard to type them.

And the products your talking about are from a different mechanism. Your talking about the bromination of ethene.

I'm talking about cholrination of methane

well. Damn. I go sounding like a smart ass and I get my **** mixed up. Sorry haha. I always get those two mixed up!
Initiation, propogation, termination... Think I'll go over that tomorrow haha

weirdspider

woopah92 wrote: »

To whoever said the need to label the questions better, I agree 10000000%. I got 89% in the mock and I forgot to put in a definition that would have given me an extra 5 marks and 90% all because I didn't see that part of the question. My fault I know, I'm going to triple check all the questions on Tues. :pac:

Argh they can be so sneaky! They give you a long definition, which as LC students we are inclined to ignore since we get them in maths, etc all the time, then you notice during corrections that theres a little question tagged on at the end and marks are lost

Hamza Malik

weirdspider wrote: »

Argh they can be so sneaky! They give you a long definition, which as LC students we are inclined to ignore since we get them in maths, etc all the time, then you notice during corrections that theres a little question tagged on at the end and marks are lost

A highlighter can be your best friend during a chemistry exam :P

weirdspider

weirdspider wrote: »

Argh they can be so sneaky! They give you a long definition, which as LC students we are inclined to ignore since we get them in maths, etc all the time, then you notice during corrections that theres a little question tagged on at the end and marks are lost

But seriously, how difficult is it to put the questions as Q.6 (a) (i) (ii) etc. like they do in Biology? I don't see why it's so difficult?

simons545

weirdspider wrote: »

Its actually 1-bromo 2-chloroethane, I like to remember that they are in alphabetical order! And yeah its 1,2 dichloroethane

it doesn't really matter for the first which way you put it I think, they give marks for both in the marking scheme. Also,thank you

simons545

Deleted User wrote: »

But seriously, how difficult is it to put the questions as Q.6 (a) (i) (ii) etc. like they do in Biology? I don't see why it's so difficult?

*hallelujah* Oh, wait, what country do we live in again?

outnumbered

Question about ethanal:
Ethanal can be prepared from Ethyne. Outline How. What term is used to describe this reaction.
Ethanal reacts with 2,4 dinitrophenylhydrazine to give solid and H2o. How can the solid be purified and how can the purity be tested? Give Name and structural formula of solid.

Slow Show

One of the mocks this year was ridiculous for the question numbering, good god. It wasn't the one I actually did but we did it in class, Examcraft I think? Like they'd ask an (a) part and 4 number-free questions later you'd hit (b). The real thing doesn't tend to be quite as bad but still, sneaky enough.

Slow Show

Slow Show wrote: »

One of the mocks this year was ridiculous for the question numbering, good god. It wasn't the one I actually did but we did it in class, Examcraft I think? Like they'd ask an (a) part and 4 number-free questions later you'd hit (b). The real thing doesn't tend to be quite as bad but still, sneaky enough.

Not only that but the markers were terrible. I think someone mentioned it already but mine was marked wrong when I had word-for-word answers from the marking scheme.

0mega

outnumbered wrote: »

Question about ethanal:
Ethanal can be prepared from Ethyne. Outline How. What term is used to describe this reaction.
Ethanal reacts with 2,4 dinitrophenylhydrazine to give solid and H2o. How can the solid be purified and how can the purity be tested? Give Name and structural formula of solid.

C2H2 CH3CHO

So the difference is H20

So, you need to hydrate ethyne to make ethanol.

How do you do it? I'm not actually sure. Addition reactions have a change in structure from planar to tetrahedral which this doesn't. I'm going to say this is a ridiculous mock question that you'd never be asked..

For the second part of the q, see above. :pac:

outnumbered

0mega wrote: »

C2H2 CH3CHO

So the difference is H20

So, you need to hydrate ethyne to make ethanol.

How do you do it? I'm not actually sure. Addition reactions have a change in structure from planar to tetrahedral which this doesn't. I'm going to say this is a ridiculous mock question that you'd never be asked..

For the second part of the q, see above. :pac:

It's actually the 1996 question. :P Oh God we have all papers/mocks back to 75. I think they are more annoying than anything

simons545

outnumbered wrote: »

Question about ethanal:
Ethanal can be prepared from Ethyne. Outline How. What term is used to describe this reaction.
Ethanal reacts with 2,4 dinitrophenylhydrazine to give solid and H2o. How can the solid be purified and how can the purity be tested? Give Name and structural formula of solid.

Dude, seriously! Don't go freaking me out with **** that's not on our course haha
Ethyne = C2H2
Ethanal = C2H3CHO
It's an addition-substitution reaction. You hydrogenate it, then replace the H with a carbonyl group. 2,4 dinitrophenylhydrazine (+methanol and sulphuric acid) is brady's reagent, which is just another test for an aldehyde.
The only reference to ethyne on our course is in the preparation of it with
CaC2 (Calcium Dicarbide) and then bubbling it through acidified copper sulfate to remove impurities.

beirtie

well guys, was wondering if I could have your opinion on studying...

do you think its better at this stage to just do exam papers? or plough through the book like I did today,but it took an eternity to get to page 60... :L

Or even briefly look over the chapter then try and do the exam papers?

outnumbered

simons545 wrote: »

Dude, seriously! Don't go freaking me out with **** that's not on our course haha
Ethyne = C2H2
Ethanal = C2H3CHO
It's an addition-substitution reaction. You hydrogenate it, then replace the H with a carbonyl group. 2,4 dinitrophenylhydrazine (+methanol and sulphuric acid) is brady's reagent, which is just another test for an aldehyde.
The only reference to ethyne on our course is in the preparation of it with
CaC2 (Calcium Dicarbide) and then bubbling it through acidified copper sulfate to remove impurities.

Oh that's okay so. As long as it's not on the course! :P Back then this was question 3

simons545

0mega wrote: »

C2H2 CH3CHO

So the difference is H20

So, you need to hydrate ethyne to make ethanol.

How do you do it? I'm not actually sure. Addition reactions have a change in structure from planar to tetrahedral which this doesn't. I'm going to say this is a ridiculous mock question that you'd never be asked..

For the second part of the q, see above. :pac:

Its a carbonyl group in the aldehydes no double bond in water unfortunately. Thank God that's not on our course anymore...

simons545

outnumbered wrote: »

Oh that's okay so. As long as it's not on the course! :P Back then this was question 3

I know yeah haha nasty stuff, I asked the same question to my 24 year old chemistry teacher and she was scratchin' her head like "ehhh, that's not on the course anymore" :pac:

Hamza Malik

The stress is getting to me. I can't remember whether we use deionised water or distilled water in the experiments

simons545

beirtie wrote: »

well guys, was wondering if I could have your opinion on studying...

do you think its better at this stage to just do exam papers? or plough through the book like I did today,but it took an eternity to get to page 60... :L

Or even briefly look over the chapter then try and do the exam papers?

I'd say your best bet is to go over the exam papers and look through the marking schemes. If you have completed the course then doing all the questions from like the last 5 years would be best, in my opinion.

simons545

Hamza Malik wrote: »

The stress is getting to me. I can't remember whether we use deionised water or distilled water in the experiments

deionised is best

beirtie

cheers thanks Simon!

MarieCurie22

simons545 wrote: »

deionised is best

You use deionised because its cheaper DISTILLED IS THE BEST!
Deionised means all ions are removed but there may still be other disolved gases etc....
Distilled H20 is by far the best as this is nothing but pure H20!

simons545

MarieCurie22 wrote: »

You use deionised because its cheaper DISTILLED IS THE BEST!
Deionised means all ions are removed but there may still be other disolved gases etc....
Distilled H20 is by far the best as this is nothing but pure H20!

Yeah haha most teachers couldn't be arsed to be honest. My teacher just used regular tap water when we did our experiments.

MarieCurie22

aoifemcg94 wrote: »

Does anyone have a rhyme thing fr the electrode potential series and the flames tests?

Electrode potential series? You mean the electrochemistry reactivity series? If so:
Pretty
Caroline
Should
Marry
A
Zulu
In
Lovely
Honolulu
Causing
Many
Strange
Gazes

And for flame tests, no but i have anion short stories?

aoifemcg94

Question on bonding.
I can never figure out whether a molecule is polar or non polar when I draw out the shape. My teacher says to see of it has a positive and negative end but I dunno I just can't seem to grasp it. I know to use the EN values too but yano sometimes they arent right, Anyone care to help?

ray2012

MarieCurie22 wrote: »

And for flame tests, no but i have anion short stories?

Post it please? :P Anything that can help me remember those tests for anions would be good!

aoifemcg94

MarieCurie22 wrote: »

And for flame tests, no but i have anion short stories?

Please enlighten me ! thanks !

meleanor

aoifemcg94 wrote: »

Question on bonding.
I can never figure out whether a molecule is polar or non polar when I draw out the shape. My teacher says to see of it has a positive and negative end but I dunno I just can't seem to grasp it. I know to use the EN values too but yano sometimes they arent right, Anyone care to help?

Take the EN values of the atoms in the molecule and figure out the difference between them.
<0.4 = negligible polarity.
0.4-1.7 = polar.
1.7< = ionic bonding.

That help at all?

MarieCurie22

ray2012 wrote: »

Post it please? :P Anything that can help me remember those tests for anions would be good!

Ok they're kinda silly but hey they help!

Chloride ion:
-Princess chloride was trapped in an aqueous solution...
-Then alone came the silver knight (silver nitrate)
-They tried getting away on his white horse percipitate...
-But the evil queen dilute ammonia comes along and dissolves percipitate! And they all dissappear...

Sulfate and Sulfite:
-Twin brothers sulfate and sulfite were out walking in the woods when they saw...
-A bear (barium chloride!)
-Both brothers get so scared they "poop" themselves (white percipitate)
-How ever Sulfite remembers the hydrogen courage liquid in his pocket (HCl)
-They both drink some, sulfite gains the courage to run like the wind and disappears...(percipitate goes)
-However his poor brother faints and his white corpse lays there forever

EoghanIRL

MarieCurie22 wrote: »

Ok they're kinda silly but hey they help!

Chloride ion:
-Princess chloride was trapped in an aqueous solution...
-Then alone came the silver knight (silver nitrate)
-They tried getting away on his white horse percipitate...
-But the evil queen dilute ammonia comes along and dissolves percipitate! And they all dissappear...

Sulfate and Sulfite:
-Twin brothers sulfate and sulfite were out walking in the woods when they saw...
-A bear (barium chloride!)
-Both brothers get so scared they "poop" themselves (white percipitate)
-How ever Sulfite remembers the hydrogen courage liquid in his pocket (HCl)
-They both drink some, sulfite gains the courage to run like the wind and disappears...(percipitate goes)
-However his poor brother faints and his white corpse lays there forever

Lol , great way to remember them .
I just learned them normally though :P

aoifemcg94

meleanor wrote: »

Take the EN values of the atoms in the molecule and figure out the difference between them.
<0.4 = negligible polarity.
0.4-1.7 = polar.
1.7< = ionic bonding.

That help at all?

I know that bit but yano sometimes when ya do that it doesn't always tell if it's polar or non polar until you draw it out? If you get what im saying