Chemistry: Post your doubts here!

[ZaqZainab]

haha thanks.
does writing uv light as one of hf is wrong?

no its not

 

[mohammed yasser]

plzzzzz guyss
I want the GT for chemistry AL May June 2013
Anyone Help????

 

[hassankhan]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w04_qp_4.pdf
Help anyone Q4 part f

 

[beeloooo]

help me with part b please
View attachment 36027

how will we figure this out?

i want help too in the same question.

 

[Someone2]

ligand exchange occurs... H2O is exchanged for Chlorine so CuCl4-2 complex forms... on adding water the opposite happens
[Cu(H2O)6]2+ + 4Cl - ⇌ [CuCl4]2- + 6H2O

hope this makes sense

 

[Someone2]

does anyone know where i can get the specimen for paper 5?? apparently it isnt on this site...

 

[BreakingBad]

I have a question > When we want to use Bond energy of Cl2 >> as its quoted in the
Data booklet it should be 242 .. but for Many time i have seen that they are using 244 as the answer !
Why? which data should we quote if the question came to us ?
one of the questions is o'n 2009 va' 41

TheZodiac
6Astarstudent

You shall quote the data according to the booklet given to you. You cannot possible remember all the bond energy values. Besides, most schools provide you with the latest data booklet so you don't have anything to worry about.

help me with part b please
View attachment 36027

how will we figure this out?

When step 1 is the slowest, we only see 1 mole of H2O2, 1 mole of I- and 0 moles of H+. Hence the order is 1,1,0.
When step 2 is the slowest, it means that step one has already taken place and looking at both the equations we can see that we have 1 mole of H2O2 and 1 mole of I- from the 1st equation and 1 mole of H+ as well, from the second equation. Hence the order is 1,1,1.
When step 3 is the slowest, both the previous steps have taken place and have to be taken into account. We see 2 moles of H+, 2 moles of I- and 1 mole of H2O2 from the equations. Hence, the order would be 1,2,2.

i want help too in the same question.

Answered above.

 

[periyasamy]

Guys got a question here.Anyone can help me explain a bit about question 7
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_4.pdf
Thank u a lot

 

[SomeStudent]

You shall quote the data according to the booklet given to you. You cannot possible remember all the bond energy values. Besides, most schools provide you with the latest data booklet so you don't have anything to worry about.


When step 1 is the slowest, we only see 1 mole of H2O2, 1 mole of I- and 0 moles of H+. Hence the order is 1,1,0.
When step 2 is the slowest, it means that step one has already taken place and looking at both the equations we can see that we have 1 mole of H2O2 and 1 mole of I- from the 1st equation and 1 mole of H+ as well, from the second equation. Hence the order is 1,1,1.
When step 3 is the slowest, both the previous steps have taken place and have to be taken into account. We see 2 moles of H+, 2 moles of I- and 1 mole of H2O2 from the equations. Hence, the order would be 1,2,2.


Answered above.

Thank you!

 

[mohammed yasser]

please please please
I have a questions about the ways to get one isomers in enantiomers of drugs
I need an explanation of getting one isomer using chiral catalyst method , and using optically active starting material method...
Please replay ASAP
Thanks..

 

[strangerss]

al salum allaykom, hello every one , can any one please explain the question 5 (iv) May/June 2010 , I don't understand how the electrode potential of the cathode becomes more negative if less pd ions are present , shouldn't less pd ions mean less oxidation took place , thus the electrode potential should be more positive ?? can any one please explain the whole thing please?

 

[Igcse stuff]

Hey guys...how can get above 30/40 in chemistry P1 .....and what should I do in order to get A* overall in Alevel chemistry...

 

[Hassan Ali Abid]

Hey guys...how can get above 30/40 in chemistry P1 .....and what should I do in order to get A* overall in Alevel chemistry...

once you solve the past pprs from 2004-2012 then u can easily score 30-36 marks easily in that ....
P1 P2 P4 ...score max marks then u can easily get an A*

 

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w04_qp_1.pdf Question 10 can anyone help me please

 

[Namehere]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_qp_1.pdf Question 10 can anyone help me please

Here you need to know two concepts/formulas:
mole fraction = number of moles of molecule A / total number of moles
Partial pressure of A = mole fraction of A x total pressure

If 20% of steam had been converted to hydrogen and oxygen, there must be 80% of steam left. So, if you before had 1 mole of steam, you now have 0.8 moles of steam (80% of 1.). Because of the 2:2:1 ratio in the equation, 2H2O ---> 2H2 + O2 , if 0.2 moles of steam had been converted into its products, then by simple stoichiometry the change for H2 is +0.2 and for O2 +0.1.

So you now have the moles of each substance present at equilibrium. If you now use the formulas from the beginning, to calculate the partial pressure, you would see you need the mole fraction of your gas and the total pressure. So, mole fraction = number of moles of molecule A / total number of moles

For steam, you have 0.80 moles, for H2 0.20 and for O2 0.10. If you add them up this give 1.1 - the total number of moles. Therefore, the mole fraction of steam is 0.80/1.1, for H2 is 0.20/1.1 and for O2 is 0.10/1.1. To get the partial pressure of each gas you now times the mole fraction of each substance by the total pressure at which the experiment is done - 1 atm. Hence for steam the partial pressure is 0.8 x 1 / 1.1 and so on...

Hope it helps.

 

[Abdel Moniem]

Thank you so much

 

[hellangel1]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w08_qp_4.pdf
please please someone help with Q4 biii
Pleasee!

 

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w05_qp_1.pdf
Question 34

 

[Namehere]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_qp_1.pdf
Question 34

The answer is B. 1 is correct for the obvious reason that OH- from the first eq (equilibrium) and H+ from the second eq would react to make H2O, leading to the position of the eq of the first eq to shift to the right, increasing the solubility of hydroxyapatite. 2 is also correct because from the second eq the phsophate ion would react with the proton, which leads to a decrease in phosphate ions. This has to be compensated and in the first eq the equilibrium shifts to the right to restore the phosphate ions, leading to an increase in solubility of hydroxyapatite once again. 3 is wrong because the statement "calcium ions react with acids" is wrong. Calcium reacts with acids, Calcium ions, however, do not (the Ca2+ ion already has its full outer shell complete and is happy as it is).

Hope this helps.

 

[Igcse stuff]

once you solve the past pprs from 2004-2012 then u can easily score 30-36 marks easily in that ....
P1 P2 P4 ...score max marks then u can easily get an A*

Thanks