You are Here: Home

# Edexcel 6CH07/01- May 8th 2013 - AS Chemistry Unit 3B Watch

1. (Original post by kiasha)
if you take the temperature difference wont the error cancel out? i mean 100-0 is 100 and 101-1 is also a hundred. so even if error was present in the thermometer reading the temperature difference obtained would still be accurate right??
I don't think taking 100 and 0 is a good idea tbh.When you take one reading off that thermometer with ±0.5'C uncertainty,you do this to find the %uncertainty, (0.5/x) times 100% cuz you took only 1 reading.However if you take two readings like 25'c and 30'c you have a combined uncertainty of 2x( ±0.5) = 1.There you took the difference between the two values and you have to consider both the uncertainties i think.As for taking 100 and 0,if you divide ±0.5 by 0 you are gonna get ∞ or possibly a math error which is ignored and taken as zero.Not 100% sure though
2. (Original post by kiasha)
hey alcohol is polar right?? it can form hydrogen bonds with water..when iodine dissolves in polar solvents it gives a brown color. so shouldnt it be brown???
Ummm, I'm confused isn't alcohol considered as an organic solvent??? :s
Because Iodine gives a brown color in water, but it dissolves better in organic solvents giving a purple solution.

Posted from TSR Mobile
3. (Original post by Daniel Atieh)
ok for the economic issue i wrote paragraph 9...wbu?
yup the same thing here
4. (Original post by Munchee)
Oops got that wrong...anyway thanks!!
you're not the only one :/
5. (Original post by awesomesoccerfan)
I don't think taking 100 and 0 is a good idea tbh.When you take one reading off that thermometer with ±0.5'C uncertainty,you do this to find the %uncertainty, (0.5/x) times 100% cuz you took only 1 reading.However if you take two readings like 25'c and 30'c you have a combined uncertainty of 2x( ±0.5) = 1.There you took the difference between the two values and you have to consider both the uncertainties i think.As for taking 100 and 0,if you divide ±0.5 by 0 you are gonna get ∞ or possibly a math error which is ignored and taken as zero.Not 100% sure though
yeah you are probably right. but the thing thats confusing me rite now is we end up gettin the same answer. suppose if there is an uncertainty of 0.5 then we get 25.5 and 30.5 or 24.5 and 29.5 right. and when we take the difference of these temperatures we end up with the same answer which is 5..right?
6. (Original post by examss)
can any1 pls tell me what to read on chemistry unit 1?
that would be formula,equations and amount of substances..energetics, atomic structure and the periodic table, bonding, introductory organic chemistry..lemme know if you want all the subtopics in each topic..okay. have fun studyng.
7. (Original post by KhawlaM)
Ummm, I'm confused isn't alcohol considered as an organic solvent??? :s
Because Iodine gives a brown color in water, but it dissolves better in organic solvents giving a purple solution.

Posted from TSR Mobile
alcohols with low carbon number are polar because of their OH group..alcohols with carbon number greater than 5 are not miscible in water. there are two opposing solubility trends depending on the OH group and the carbon chain resistance. so butanol would be polar and hence color of iodine in it would be brown i guess.
8. If I put the right number for the value of the enthalpy change but forgot the sign, how much does it cost me? Do I get any marks at all for the question?
9. (Original post by TheUndercoverPanda)
If I put the right number for the value of the enthalpy change but forgot the sign, how much does it cost me? Do I get any marks at all for the question?
One mark for sign. You'll get the rest.

Posted from TSR Mobile
10. Also I think that the iodine disappearing question has stirred up quite the controversy =_= till now I have seen about 5 different answers and I'm pretty sure I got it wrong
11. (Original post by Relaxedexams)
One mark for sign. You'll get the rest.

Posted from TSR Mobile
Ahh ok thanks
12. (Original post by TheUndercoverPanda)
Ahh Biology and Chemistry Unit 3b exams are a horrible way to start the exams off in my opinion, so many stupid mistakes from the start ;________;
I think they make us start with the unit 3 papers because they're supposed to be easy. (well, apparently not this time!) I'm trying my best to forget about that awful graph that came in the physics paper. I hope the grade boundaries go super low, but I think it's unlikely.
I think they make us start with the unit 3 papers because they're supposed to be easy. (well, apparently not this time!) I'm trying my best to forget about that awful graph that came in the physics paper. I hope the grade boundaries go super low, but I think it's unlikely.
Good thing I decided not to take physics this year then haha
14. (Original post by TheUndercoverPanda)
Good thing I decided not to take physics this year then haha
Curse you.
15. Relaxedexams man for the obswrvation one...what u c....i wrote like decrese in size, bubbles seen ...like tht...is it acceptable? and for the mass of mixture..was it 50 or 55? and the one after step 7 is re-distillation?
16. what are the observations seen in that iodobutane one ? is it only purple vapour
17. (Original post by wbrian)
what are the observations seen in that iodobutane one ? is it only purple vapour
Yellow solid

Black solid

(Maybe) steamy fumes

Purple vapour is correct

Posted from TSR Mobile
18. (Original post by Daniel Atieh)
Relaxedexams man for the obswrvation one...what u c....i wrote like decrese in size, bubbles seen ...like tht...is it acceptable? and for the mass of mixture..was it 50 or 55? and the one after step 7 is re-distillation?
Are you talking about the carbonate observation? If so then I wrote solid disappears. What you wrote is also correct, not wrong.

Mass was mass of solution. That was 50?

Step 7 is fractional distillation.

Posted from TSR Mobile
19. (Original post by Relaxedexams)
Are you talking about the carbonate observation? If so then I wrote solid disappears. What you wrote is also correct, not wrong.

Mass was mass of solution. That was 50?

Step 7 is fractional distillation.

Posted from TSR Mobile
yes 50...i wrote re-distillation....can be accepted right?
20. (Original post by Relaxedexams)
Are you talking about the carbonate observation? If so then I wrote solid disappears. What you wrote is also correct, not wrong.

Mass was mass of solution. That was 50?

Step 7 is fractional distillation.

Posted from TSR Mobile
yes 50...i wrote re-distillation....can be accepted right?

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: May 21, 2013
Today on TSR

Can it be done?

### Give feedback to Cambridge here

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Useful resources

Can you help? Study Help unanswered threadsStudy help rules and posting guidelines

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE