Chemistry P4| A2 only

[Zishi]

well....it was written in the book.....so this cnfusion came into my mind

So the answer must be written in the book - which book is that btw?

 

[histephenson007]

c
5d ii.....with HCl the basic phenylamine will immediately react to for C6H5NH3+Cl-...bt we wanted just plain old phenyl amine....dats why we add NaOH

got it, thanx!

 

[girlscampisra]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_42.pdf

This paper is kinda tough. Does anyone know the GT for this?

Meanwhile, my questions from dis papers :

2.b) Can someone explain the calculations. Again, I've said this before, WHY is lattice enthalpy positive?!
3.d)i) dafuq?? we should find out the answers by trial and error method or what/??? also include ii) plz
5.d)ii) I don't get why we need to add NaOH at the end?!

Please help me, you're sure to get a like even for trying, I'm a likaholic

lattice enthaply is not +ve .. where is it stated that it is positive ? it is enthalpy of hydration that is equal to n opposite to latt. enthalpy.. therefore positive.

 

[histephenson007]

lattice enthaply is not +ve .. where is it stated that it is positive ? it is enthalpy of hydration that is equal to n opposite to latt. enthalpy.. therefore positive.

In the markscheme, the value for lattice enthalpy is just directly given as a positive value. That's why I got confused. AND, in pg 225 of the A level Chemistry book (look at the graph).


But what u say makes sense, its opposite to hydration enthalpy, so positive. I'll just hav to go with that into the exam.

 

[Amy farvin]

when double bond breaks , the primary carbon forms co2 , secondary forms carboxylic acid while tertiary forms ketone.. as u can see double bond is between primary n tertiary carbon the products will be co2 n ketone!

thanx a lot..

 

[Amy farvin]

Candidates should be aware that all
β-sheets contain (roughly) the same density of hydrogen bonds – between the C=O and N-H
groups in the peptide bonds of adjacent chains. The side chains poke up and down from the plane
of the sheet. It is the interactions of these side chains between the sheets that is important for
flexibility: if these interactions are weak van der Waals (as in silk, with glycine and alanine
residues), then the sheets are flexible, If, however, the interactions are covalent S-S bridges, then
the sheets cannot slide over each other so easily, and so are more rigid.

thanx loadz....

 

[zain tariq]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_4.pdf
I think the ms is wrong concerning the values in the table in question 2!plz explain

 

[smzimran]

In the markscheme, the value for lattice enthalpy is just directly given as a positive value. That's why I got confused. AND, in pg 225 of the A level Chemistry book (look at the graph).


But what u say makes sense, its opposite to hydration enthalpy, so positive. I'll just hav to go with that into the exam.

If you are still having problems with lattice enrgy being positive or negative,
Check this link:
http://www.chemguide.co.uk/physical/energetics/lattice.html#top

Read the section titled:
What is lattice enthalpy?

 

[girlscampisra]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_4.pdf
I think the ms is wrong concerning the values in the table in question 2!plz explain

yes plz smbody solve this.. i dont understand why is A n B 1 in 2 n 3rd part..

 

[hassam]

important......myt cum up in exam
bt problem is why there is this two humped shape

 

[girlscampisra]

oops i mean A only.. why is a 1 in 2nd n 3rd part

 

[girlscampisra]

important......myt cum up in exam
bt problem is why there is this two humped shape

i guess it shows endothermic n exothermic both changes n the net change is them exothermic.. thats why 2 humps.

 

[girlscampisra]

the reaction is first endothermic, then exothermic.. n overall reaction being exothermic.

 

[smzimran]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_4.pdf
I think the ms is wrong concerning the values in the table in question 2!plz explain

No, it is right!

If 1st step is slowest overall,
order of reaction is 1st order w.r.t H2O2 and I- because they are present in the 1st rate determining equation.


If 2nd step is slowest,
order of reaction is 1st order w.r.t H+
but the second reactant is IO- this is formed by the 1st reaction!
So in this case, we have to take both the 1st and second reaction into account!
Therefore order of reaction is 1st order w.r.t H2O2 and I- also


If 3rd is slowest,
HOI- cannot be formed unless 2nd equation is taken into account and IO- cannot be formed until 1st in taken into account!

So, in this we have to see all three equations (only the reactants side)
H2O2 appears once so it is 1st order
I- appears twice (in equations 1 and 3)
H+ appears twice (in 2nd and 3rd equations)

I hope you got the point!

 

[girlscampisra]

No, it is right!

If 1st step is slowest overall,
order of reaction is 1st order w.r.t H2O2 and I- because they are present in the 1st rate determining equation.


If 2nd step is slowest,
order of reaction is 1st order w.r.t H+
but the second reactant is IO- this is formed by the 1st reaction!
So in this case, we have to take both the 1st and second reaction into account!
Therefore order of reaction is 1st order w.r.t H2O2 and I- also


If 3rd is slowest,
HOI- cannot be formed unless 2nd equation is taken into account and IO- cannot be formed until 1st in taken into account!

So, in this we have to see all three equations (only the reactants side)
H2O2 appears once so it is 1st order
I- appears twice (in equations 1 and 3)
H+ appears twice (in 2nd and 3rd equations)

I hope you got the point!

you mean we take into account ALL the reactions?!

 

[zain tariq]

hmm thanks a lot!I was thinking the same initially but the way our teachers have taught us that u only the reactant involved in the slowest step appears in the rate equation confused me

 

[princesskt]

can u plz draw the structure............

again asking plz draw the structure any 1

 

[smzimran]

you mean we take into account ALL the reactions?!

Exactly!
But this is true in this specific case, may nit be in others though so be careful!

 

[smzimran]

This question was asked by musa Khan...
Q3 (e)(iv):


Q7 (c)(ii):
Very simple, because it says that the M and M+2 peaks are of the same height.
This is true for Br only!
If it was Cl, the peak heights would be in the ratio of 1:3

 

[histephenson007]

If you are still having problems with lattice enrgy being positive or negative,
Check this link:
http://www.chemguide.co.uk/physical/energetics/lattice.html#top

Read the section titled:
What is lattice enthalpy?

THANK YOU VERY MUCH. That solves it