Chemistry: Post your doubts here!

[smzimran]

May/jun 03 paper1 Q 2,13,29. PLEASE HELP!
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s03_qp_1.pdf

2.
B is the answer.
(There are 3 double bonds initially)
They are saying one of its side chains should be converted into a long chain with 2 double bonds still left, that means 1 double bond should be hydrogenated.
And they are saying two side chains should be converted into a long chain with 1 double bond, that means 2 double bonds should be hydrogenated in both (2 * 2 = 4 in total)
Total number of bonds that need to be hydrogenated are = 4 + 1 = 5
So, 5 moles H2 are needed.

13.
C is the answer.
In this case, for the mixture to be neutral, there can be two possibilities:
1. Both oxides are amphoteric
2. One oxide is acidic and the other is basic
Now, lets check,
A: Al2O3 is amphoteric and MgO is basic
B: Both are basic
C: Na2O is basic and P4O10 is acidic
D: Both are acidic
C matches the criteria so it is the answer

29.
C is the answer.
You should know H2SO4 (conc.) is needed for this reaction
And to purify ethene from any additional amount of acid added, an alkali is bubbled through to neutralise the effect of the acid

 

[smartangel]

thanks alot!
also tell me 20 of the same paper..i always get confused with such questions.

 

[Muhammad Bin Anis]

could you please explain Q 13 again.
i already know all that you explained
but why isnt the answer not magnesium because it is closest to aluminium in the periodic table
so that means its electronegativity must be most similar to aluminium.

and for question 38 the correct answer is A.
i just realized that option 3 (HOCH2CH2OH) which is a diol is formed when ethene is reacted with cold, dilute acidified potassium manganate.

in Magnesium's case
U just go back so just decrease the e.n value
when u move up u increase it .
From Aluminium go back to magnesium and then up to beryllium

 

[hmlahori]

in Magnesium's case
U just go back so just decrease the e.n value
when u move up u increase it .
From Aluminium go back to magnesium and then up to beryllium

oh ok got it now thanks!

 

[hmlahori]

For 08. in q8 you just have to recall Boyle's Law and Charle's Law. its D. as per charles law volume is propotional to temp.
in 14.. you need to look at the periodic table. option B C D form ionic compounds. Aluminium, on the other hand is in group3 hence can form covalent compounds. like AlCl3.
Plese have a look at my questions in the previous post and see if you can help me out. thanks

i understand question 14 but for question 8 why cant the answer be A because that also makes sense. pressure is inversely proportional to volume at constant temperature?

 

[Amy Bloom]

Hello there!
I've a series of doubts which i would be grateful if you could clarify them for me & check my answers.

(1) For the Nickel-Cadmium cell, the electrode reactions are given below: [--> means "in equilibrium with"]
Cd(OH)2 (s) + 2electrons --> Cd (s) + 2OH-
NiO(OH) (s) + H2O (l) + electron --> Ni(OH)2 (s) + OH- (aq)
Make a summary of the cell.
My answer: NiO(OH) | NiO(OH)2 || Cd | Cd(OH)2

(2) What is the role of KOH (aq) in the Nickel-cadmium cell?
My answer: To provide the OH- ion for reaction to occur.

(3) Predict the change in Electrode potentials in cell of the Daniell cell of the concentration of (i) CuSO4 is increased and (ii) ZnSO4 is increased?

Request : Reply as soon as possible ​

 

[sumaiyarox:)]

can someone plzzz explain the reflux thing in brief....n also question 5e from paper 2 may june 10.??
plzzzzz

 

[sumaiyarox:)]

what volume of oxygen ,measured at room temperature and pressure,is required for the complete combustion of 8.65g of H2S ?
plzz help..howz this done..??

 

[xhizors]

AsSalamalikum wr wb, i have some question from w11 qp 11 Please help, May Allah(swt) help you and make your way easy for Distinctions Ameen.
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w11_qp_11.pdf
Q4
Q6
Q2
Q1
Q8 why ? HSO3- is donating H means proton donor means acid
Q10
Q14
Q15
Q18
Q16
Q20
Q3
Q9
Q22
Q23

 

[smzimran]

can someone plzzz explain the reflux thing in brief....n also question 5e from paper 2 may june 10.??
plzzzzz

Heating under reflux means heating without having the risk of the liquid evaporating or splashing off the flask
A liebag condenser condenses the evaporaing liquid back into the flask

A Request:
Plz post the link to your questions

 

[smartangel]

i need help with Nov 03 Q 28.
.http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w03_qp_1.pdf

 

[smzimran]

i need help with Nov 03 Q 28.
.http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_qp_1.pdf

Only the hydrogen atoms in OH will be substituted
There are 3 OH groups so, B is the answer !

 

[smartangel]

Only the hydrogen atoms in OH will be substituted
There are 3 OH groups so, B is the answer !

thanks...but i dont get it.. why not the other hydrogen atoms?

 

[smzimran]

thanks...but i dont get it.. why not the other hydrogen atoms?

Bcoz D2O is water my dear it forms D+ and OD- ions thats why they substitute only OH groups
Btw, C-H bonds are non polar

 

[smartangel]

Bcoz D2O is water my dear it forms D+ and OD- ions thats why they substitute only OH groups
Btw, C-H bonds are non polar

thanks a lot bro!! okay this might get annoying for you but since my chem is kinda bad so here"s one more question..Q20 0f the following paper.
http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s03_qp_1.pdf
such questions are there in almost every paper and i always get them wrong.. how exactly do we do them?

 

[smzimran]

thanks a lot bro!! okay this might get annoying for you but since my chem is kinda bad so here"s one more question..Q20 0f the following paper.
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s03_qp_1.pdf
such questions are there in almost every paper and i always get them wrong.. how exactly do we do them?

I also have not been able to figure out a shortcut to such questions
Here are possible structures:
ClCH2 - CH = CHCl [2 isomers of this cis and trans]
CH3 - CCl = CHCl [2 isomers of this cis and trans]
CH3 - CH = CCl2
Cl2C - CH = CH2
ClCH2 - CCl = CH2

 

[smartangel]

yeah because making all the structures is going to be time consuming..but thanks a lot!

 

[smzimran]

yeah because making all the structures is going to be time consuming..but thanks a lot!

Yes, takes 3-4 minutes!

 

[sumaiyarox:)]

Heating under reflux means heating without having the risk of the liquid evaporating or splashing off the flask
A liebag condenser condenses the evaporaing liquid back into the flask

A Request:
Plz post the link to your questions

thnx..il post the link.. sorry..

 

[whocares]

Q5 part b?? I am not getting the right answer. Please help!