Edexcel CHEMISTRY DOUBTS!!!!

[KJ1995]

wow ............really it's very helpful  
Thanks alot pal  
 Have you got notes similar to that one for unit 5 I wonder if you can post it soon plz  

Anytime

Unfortunately, i dont have the unit 5 notes, didnt look for them since im doing u4 only in jan.. Sorry :/
 

[KJ1995]

Can anyone tell me what are internal assessment tasks? And how do they help? im doing u4 chem in jan

[Assi1993]

heelloo frieds can anyone pleasseeeeee solve this question today?? its urgent..

8.   A gaseous organic compound, X, was burnt in an excess of oxygen. A 0.112 dm  sample of X, measured at s.t.p., produced 0.88 g of carbon dioxide.
How many carbon atoms are there in one molecule of X?
 waiting
thankuuuu SF

[Romeesa-Chan]

heelloo frieds can anyone pleasseeeeee solve this question today?? its urgent..

8.   A gaseous organic compound, X, was burnt in an excess of oxygen. A 0.112 dm  sample of X, measured at s.t.p., produced 0.88 g of carbon dioxide.
How many carbon atoms are there in one molecule of X?
 waiting
thankuuuu SF

-Noting that 1 mole of CO2 has 1 mole of Carbon,
use molar mass to find moles of carbon present:
( 0.88 g CO2 ) ( 1 mol Carbon / 44.01 g / ml CO2) = 0.02 moles of carbon


-Use the molar volume of gases at STP, to find moles of compound:
(A 0.112 dm^3) ( 1 mole of gas @STP / 22.4 dm^3) = 0.005 moles of compound


-Find how many moles of carbon in 1 mole of compound:
0.02 moles of carbon / 0.005 moles of compound = 4 moles of Carbon / mole compound


-If so, then there are 4 atoms of Carbon in 1 molecule of compound.


Credit goes to original poster. (:

[Romeesa-Chan]

Can anyone tell me what are internal assessment tasks? And how do they help? im doing u4 chem in jan

Task for what ?

[KJ1995]

Task for what ?

 I dont know.. They are like tasks for unit 4, i dont have them, and i dont know if they are important so im just asking
Thanks anyways

[Romeesa-Chan]

I dont know.. They are like tasks for unit 4, i dont have them, and i dont know if they are important so im just asking
Thanks anyways

Just go through the syllabus properly when studying. (:
No problem. (:

[KJ1995]

Need help in this question please
HA(weak acid) is being titrated with NaOH(aq)..A titration curve is drawn, the end point was somewhere between 9.0 and 9.4 pH. So the question was to use the curve to find the pH of an aqueous of NaA. The answer was between 9.0 and 9.4. Can someone please explain why? Is there a rule or something?, and make sure that your explanation is not just for this question (i mean that if i encounter a similar question, i want to know how to solve it)

Thank you for your help

[The Golden Girl =D]

AQA January 2007 Question 4 (Paper Attached Hopefully =])

I don't get how we come up with   d]ii) ... and e]iii)

(Yes .. It's in OUR Edexcel Syllabus! )

Thanks in Advance =]

[The Golden Girl =D]

Anyone =/

[Deadly_king]

AQA January 2007 Question 4 (Paper Attached Hopefully =])

I don't get how we come up with   d]ii) ... and e]iii)

(Yes .. It's in OUR Edexcel Syllabus! )

Thanks in Advance =]

4.(d)[ii] Isomer L has 2 hydroxyl groups while pentane dioic acid has 2 carboxyl groups. THe polymerisation therefore is going to be between one hydroxyl amd ome carboxyl group. This is known as an Ester Linkage which is a condensation polymerisation.

This may hopefully help you understand.

4.(e)[iii] AM sorry but I've forgotten about NMR
However am pretty sure you should first identify the two peaks in question. Only then will you be able to find the answer

Am sorry for not being able to clear your doubt 

[Deadly_king]

Need help in this question please
HA(weak acid) is being titrated with NaOH(aq)..A titration curve is drawn, the end point was somewhere between 9.0 and 9.4 pH. So the question was to use the curve to find the pH of an aqueous of NaA. The answer was between 9.0 and 9.4. Can someone please explain why? Is there a rule or something?, and make sure that your explanation is not just for this question (i mean that if i encounter a similar question, i want to know how to solve it)

Thank you for your help

The end-point usually refers to the pH of the solution which results after titration This is why the pH of NaA is between 9.0 and 9.4 just like that of your end-point

I'll take an example:

Let's say you are titrating HCl with NaOH. The resulting solution is NaCl and H₂O has pH 7. Have you ever wondered why is that so?

It's simple, all the H⁺ ions from HCl have been neutralised by OH^- ions from NaOH. Therefore only NaCl remains which is a neutral solution. We can hence conclude that the end-point would definitely lie at pH 7. However depending on the concentrations of the acid or base, the end-point may alter

Hope I've been helpful

[KJ1995]

Anyone =/

Im not sure if im answering you fully but from what i know.. 2 peaks mean that C atom has an adjacent C atom what contains 1 hydrogen ( N:number of hydrogen atoms adjacent; N+1=Number of peaks) Now for the other its 4 peaks so 4 = N+1, N=3, so it there is a C atom with 3 hydrogens too.. Which means there is CH3 and CH.. Now i checked the markscheme, the answer was something like CH3(-)CH(O)..Im not sure but something like that..I dont why did they write it that way and i dont why is the oxygen there, if by any chance u figure out why, could u please tell me?

Hope I've helped

[KJ1995]

CO2(aq) + H2O(l)   <-reversible->   H+(aq) + HCO3–(aq).... Why is HCO3- a base?

[Deadly_king]

CO2(aq) + H2O(l)   <-reversible->   H+(aq) + HCO3–(aq).... Why is HCO3- a base?

Bases can also be defined as proton acceptors

In this case, the base HCO₃^- is accepting H⁺ to give H₂O and CO₂

This is why it is known as a base