Chemistry Revision

[1bilalm]

i just kinda really give up for chemistry

 

[JmCullen]

how can we know the errors in setting up an experiment?
i'm always stuck there, where they always ask, what are the 2 errors in setting up this experiment.. (in paper 5 chemistry)
then.. how can the errors be change?
so? any tips to observe the errors? instead of guessing around =__=ll

 

[skittles]

is this specifically for paper 6? please temme

 

[AliHaider1011]

Does any one has the list of all salts and their colours.....??

 

[xIshtar]

how can we know the errors in setting up an experiment?
i'm always stuck there, where they always ask, what are the 2 errors in setting up this experiment.. (in paper 5 chemistry)
then.. how can the errors be change?
so? any tips to observe the errors? instead of guessing around =__=ll

The common apparatus errors are usually that gas is collected in correctly, ie the tube is the right way up and it should be upside down, or that the tube is passing it through water, when it needn't be. Another common error could be heating the wrong thing when a catalyst is involved. It all depends on the experiment, but just keep these in mind.

 

[WW66F1980]

I've come across a question on the May/June 2009 IGCSE Chemistry Paper 3 past paper exam.

It's question 5(b) (first variant) of this paper: http://www.xtremepapers.me/CIE/Cambridg ... 9_qp_3.pdf

I've checked the mark scheme and all is says is T3(PO4)2 but I've no idea why that's the answer. I know it's something to do with mole ratio but really can't work it out!

Please help someone.

 

[JmCullen]

how can we know the errors in setting up an experiment?
i'm always stuck there, where they always ask, what are the 2 errors in setting up this experiment.. (in paper 5 chemistry)
then.. how can the errors be change?
so? any tips to observe the errors? instead of guessing around =__=ll

The common apparatus errors are usually that gas is collected in correctly, ie the tube is the right way up and it should be upside down, or that the tube is passing it through water, when it needn't be. Another common error could be heating the wrong thing when a catalyst is involved. It all depends on the experiment, but just keep these in mind.

ohh.. okok! thanks alot!

 

[AStarHunter]

Thanks sooo much !!
But I have one tiny question, in paper 6, november 2010 ( link: http://www.xtremepapers.me/CIE/Cambridg ... _qp_62.pdf) they ask for a test for ethanol and in the mark scheme (http://www.xtremepapers.me/CIE/Cambridg ... _ms_62.pdf) it says lightened splint and flame produced. Is this exactly what I am supposed to write ? or are there any other details i have to include like flame colour ?

 

[xIshtar]

Thanks sooo much !!
But I have one tiny question, in paper 6, november 2010 ( link: http://www.xtremepapers.me/CIE/Cambridg ... _qp_62.pdf) they ask for a test for ethanol and in the mark scheme (http://www.xtremepapers.me/CIE/Cambridg ... _ms_62.pdf) it says lightened splint and flame produced. Is this exactly what I am supposed to write ? or are there any other details i have to include like flame colour ?

As ethanol is an alcohol, the obvious choice of test will be as you said a flame produced from a lit splint. The flame colour is not required, as it is not in the syllabus. Hope I helped

 

[AStarHunter]

Thanks that was really helpful. :good:
I have another question in the same paper: http://www.xtremepapers.me/CIE/Cambridg ... _qp_62.pdf
q3(f) i know that the line is going to be to the left of the original one but is the time supposed to be halfed so instead of 15 mintues, does it end at 7.5 minutes (half the time cause it is more concentrated?)
Sorry for being annoying ardon:

 

[xIshtar]

Thanks that was really helpful. :good:
I have another question in the same paper: http://www.xtremepapers.me/CIE/Cambridg ... _qp_62.pdf
q3(f) i know that the line is going to be to the left of the original one but is the time supposed to be halfed so instead of 15 mintues, does it end at 7.5 minutes (half the time cause it is more concentrated?)
Sorry for being annoying ardon:

It doesn't specify by how much the concentration is increased by, so it is not correct to assume that it would be half the time. It is not being annoying, rather uplifting for me to help people to be honest .

So, I guess I didn't really answer, sorry for rambling xD. Basically, anywhere to the left is accepted as the rate of reaction would increase. Just note, that as there is no extra reactants, the final mass decrease will be the same.

Glad to help

 

[AStarHunter]

Thank you again :lol:
And I am glad I wasn't annoying

 

[ssms396]

i have a question....
usually the last questions are about conducting our own experiment related to the topic given.....
and they provide a specific number of lines to write our answers....is it ok if we use more lines than provided....
i mean...if they give 5 lines...can we write more than that?

what about for other questions?

(i hav a bad habit for writing lots.)

 

[xIshtar]

i have a question....
usually the last questions are about conducting our own experiment related to the topic given.....
and they provide a specific number of lines to write our answers....is it ok if we use more lines than provided....
i mean...if they give 5 lines...can we write more than that?

what about for other questions?

(i hav a bad habit for writing lots.)

As do I. I read a Cambridge FAQ the other day, and basically the lines are for what they think you should write, ie, the amount.. I usually write more, so I guess it isn't catastrophic cause it will still be read and marked.

 

[ssms396]

okay...so
its doesn't make a difference..right?
they won't deduct marks, will they?

 

[HorsePower]

i think the maximum u can exceed is only 1 line

 

[zkapoor]

Hey, had a slight doubt with experimental techniques for paper 6 and was wondering if someone could help me.

It's about the types of distillation
My chem teacher told me a while back that you use simple distillation for 2 liquids with boiling points with a difference of greater than 25 degrees and fractional for liquids with a difference of less.
The study guide says simple distillation separates "A volatile liquid from a solution with a non volatile solid" and fractional distillation separates "liquids with different boiling points (the liquids have to be miscible)"

Which is right?

 

[ssms396]

zkapoor...
i would say that the study guide is correct because we don't apply simple distillation to separate ethanol and water even though they have a difference 25 degrees in their boiling points.
and anyway, how will you know in the exam whether the two liquids have a difference of 25 degrees in their boiling points.
its safer to go with fractional distillation to seperate two miscible liquids.



i have another question....recently i noticed that in the past papers they used "diffusion" as a seperation technique. How does that work?
My chemistry teacher never told us how to use diffusion to seperate substances.

 

[HorsePower]

can u tell me which paper is that in ?

 

[Zardonz]

guys can any1 help me? i need help with a math thing but no1 is answering please check the math doubts post Appr.