• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

Chemistry: Post your doubts here!

M

MaxStudentALevel

Messages
199
Reaction score
138
Points
43
iKhaled said:
ofc!! because the next coming days i will be doing paper 5 mostly and i will need u and all the other paper 5 candidates to discuss stuff about it and doubts like how yesterday we kept discussing. i guess this will help us to score a good grade, right ?
Click to expand...

Yes! Exactly!!! :) I have an English exam thursday so today is my final prep for P5 until Thursday. Then on Thursday I'll be able to discuss! :)
 
iKhaled

iKhaled

Messages
869
Reaction score
374
Points
73
Alice123 said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_22.pdf
Q3e) i know this is very stupid, bt please explain y CHO is wrong iKhaled
Click to expand...
you have the ratio to 1 : 1.341 : 1.166 they r not 1:1:1 so multiply all of them by 2 then see if the numbers u get are close to a whole number like for example 4.999 or 4.0021 or kinda close to a whole number if 2 is wrong then multiply by 3 if not then by 4 and go on i found that multiplying by 6 gives me a good answer to the 3 of them so it will be C6H8O7..try it out and tell me if you got it. Dont be fooled that when u have 1:1.430:1.22 u think all of them are one
 
Alice123

Alice123

Messages
561
Reaction score
733
Points
103
iKhaled said:
you have the ratio to 1 : 1.341 : 1.166 they r not 1:1:1 so multiply all of them by 2 then see if the numbers u get are close to a whole number like for example 4.999 or 4.0021 or kinda close to a whole number if 2 is wrong then multiply by 3 if not then by 4 and go on i found that multiplying by 6 gives me a good answer to the 3 of them so it will be C6H8O7..try it out and tell me if you got it. Dont be fooled that when u have 1:1.430:1.22 u think all of them are one
Click to expand...
How many years do u think is betr to solve?
 
iKhaled

iKhaled

Messages
869
Reaction score
374
Points
73
Shai_n said:
im confused with carbonyl and also on when to use tollens reagent
Click to expand...
carbonyls are organic compounds that have the C=O formula. they give orange ppt when tested with 2,4-DNPH

NOTE: carboxylic acids has the C=O group but it doesn't give a positive test with the 2,4-DNPH. Both aldehydes and ketones have carbonyl groups and they give positive results with 2,4-DNPH

since both ketones and aldehydes give positive results with 2,4-DNPH we cant use this test to compare between them so we use either tollen's reagent or fehling's reagent.

both of them give a positive reuslt with aldehyde but a negative result with ketones (no reaction) with tollen's you will have a silver mirror/silver ppt. with aldehydes and fehling's reagent will turn from blue solution to brick red.

i hope you got it!
 
D

Dr.MMM

Messages
35
Reaction score
19
Points
18
According to the marking scheme the answer is:
G is HOCH2COCH2OH as the minimum (1)
allow the gem diol CH3COCH(OH)2
But the empirical formula is C6H8O7

Explain why?
 
iKhaled

iKhaled

Messages
869
Reaction score
374
Points
73
Dr.MMM said:
According to the marking scheme the answer is:
G is HOCH2COCH2OH as the minimum (1)
allow the gem diol CH3COCH(OH)2
But the empirical formula is C6H8O7

Explain why?
Click to expand...
first of all the empirical formula is given as CH2O with Mr =90 so the molecular formula is c3H6O3. where did you get C6H8O7 from? :eek:
 
You must log in or register to reply here.
Top