Chemistry: Post your doubts here!

[Amy Bloom]

I got most of it but, why did you put a 2 next to H2O and how is it an oxidising agent?

It lost an Oxygen atom. So reduction has taken place. So it is an oxidising agent.
I put a two there because one more electron is lost from there (the "extra" electron)

 

[sagystu]

hey everybody , i need some classified past papers to paper 2 or paper 4 ? can any body help me with that pleaseeeeeeeeeeeeeee

thanks a lot in advance

 

[asexamskillme111]

Can anyone help me with 2008 Oct/Nov paper 4 question 2 (b).
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w08_qp_4.pdf
I don't understand how they got the numerical values. Thank you.

 

[Navi Don]

can anyone tell me how enthalpy change of hydration decreases with increasing size of ion?

 

[iKhaled]

can anyone tell me how enthalpy change of hydration decreases with increasing size of ion?

hey i think its like that..

when the size of the ion increases they have weaker charge density because now the same charge spreads over a larger volume. weaker charge density means they will not strongly attract the dipoles of water molecules so they will be less soluble in water and therefore they will have a more positive or less negative value of enthalpy change of hydration.

makes sense ?

 

[asexamskillme111]

Can anyone help me with 2008 Oct/Nov paper 4 question 2 (b).
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w08_qp_4.pdf
I don't understand how they got the numerical values. Thank you.

 

[Gémeaux]

Can anyone help me with 2008 Oct/Nov paper 4 question 2 (b).
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w08_qp_4.pdf
I don't understand how they got the numerical values. Thank you.

b) Each option gives a case choosing one of the three to be the slowest step, which the rate-determining step. The reactants of the equation in every case should appear in the rate equation if they affect the equilibrium. Taking step I, we have H2O2 + I– ---> IO– + H2O , this has H2O2 and iodide but no hydrogen ions. so the order for hydrogen would be zero, and that for the other two, 1.
a=1, b=1, c=0

Step II: (IO-) + (H+) ---> HOI here there is hydrogen so for c =1, but the other reagent is an intermediate that *never* appear in a rate equation. the intermediate was formed using H2O2 and I- so the instead of IO-, these would appear i.e.
a=1 and b=1, c=1

Step III: The equation is HOI + H+ + I– ==> I2 + H2O
there is again an intermediate HOI, this was formed using H+ and IO-. This means that there would be two sources of hydrogen ions, one the third equation and the other the second equation, giving c=2. IO- takes us back to the first equation, which uses H2O2 and I-, leaving us again with two sources of I- ( the third eq. and the first one) so b=2. H2O2 comes only once, so a=1.
a=1, b=2, c=2.

Hope it helps.

 

[fatemakhan]

can anyone ans this for me....?
1)explain why hydrogen is evolved more slowly from methanoic acid solution than a HCL solution?
2)explain why, eventually,the methanoic acid sol produces as much hydrogen as the HCL solution?
add data given: Methanoic acid and hcl both are being reacted to an excess of Magnesium powder .
For a fixed amount of Mg, the rate equation for the reaction is:
rate= k [H+(aq)]
the paper:http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_qp_4.pdf

question is 2

 

[Navi Don]

hey i think its like that..

when the size of the ion increases they have weaker charge density because now the same charge spreads over a larger volume. weaker charge density means they will not strongly attract the dipoles of water molecules so they will be less soluble in water and therefore they will have a more positive or less negative value of enthalpy change of hydration.

makes sense ?

yes its right thanks alot i was also thinking that charge density had rolo in this

 

[freezingfires]

I need URGENT help on this paper 5 question​

I have a question from May June 2008 PAPER 5 Q2 part f, i don't get how to draw these lines do we need to find the value and which x and y values to take? can someone plz explain.

f)Draw construction lines on the graph to derive values to enable you to calculate

the relative formula mass of the basic copper(II) carbonate and the value of x in
CuCO3.Cu(OH)2.xH2O.
Values read from graph, including units
x-axis ...................................................... y-axis ...........................................................
Calculation of the relative formula mass, Mr
[Ar: H, 1.0; C, 12.0; O, 16.0; Cu, 63.5]​

 

[MONJUR HASAN NISHAD]

I need resources for chemistry practical. Someone help me!

 

[nafis shahRiyar]

notes needed for chemistry paper 3 !!

 

[nafis shahRiyar]

notes needed for chemistry paper 3 !!

 

[nafis shahRiyar]

notes needed for chemistry paper 3 !!

 

[amanbro]

thanks a lot guys..!!!!!!!!!!

 

[amanbro]

Hi everyone, AsSalamoAlaikum Wr Wb..

To get things organized in a better way, I am making this thread. As othewise, some queries remain unanswered!

So post your CHEMISTRY doubts in this thread. InshaAllah members around will help you.

Any Chemistry related notes and links will be added here in this post. Feel free to provide the links to your notes around the forum, or any other websites!

Chemistry Notes:


http://www.chemguide.co.uk This is the website, which contains almost everything classified according to the syllabus.

Tips for solving chemistry MCQs 9701/01

Chemistry P5 Tips and Notes

Some links & Notes - by 'destined007'

Chemistry worksheets Link shared by hassam

Chemistry Application Booklet: Mistakes and Corrections!

Calculations for A level Chemistry, author E.N. Ramsden third edition ebook download.


Regards,
XPC Staff.

thanks bro..!!!

Hi everyone, AsSalamoAlaikum Wr Wb..

To get things organized in a better way, I am making this thread. As othewise, some queries remain unanswered!

So post your CHEMISTRY doubts in this thread. InshaAllah members around will help you.

Any Chemistry related notes and links will be added here in this post. Feel free to provide the links to your notes around the forum, or any other websites!

Chemistry Notes:


http://www.chemguide.co.uk This is the website, which contains almost everything classified according to the syllabus.

Tips for solving chemistry MCQs 9701/01

Chemistry P5 Tips and Notes

Some links & Notes - by 'destined007'

Chemistry worksheets Link shared by hassam

Chemistry Application Booklet: Mistakes and Corrections!

Calculations for A level Chemistry, author E.N. Ramsden third edition ebook download.


Regards,
XPC Staff.

 

[iKhaled]

hello,

can any chemist please explain why when mixing two solutions of equal volume their concentration is diluted by 2 ???

 

[Student12]

I have a question which is on rate of reaction,

PCl3 + Cl2 ----> PCl5

[PCl3]/M [Cl2]/M Rate
0.36. 1.26. 6.0x10^-4
0.36. 0.63. 1.5 x 10^-4
0.72. 2.52. 4.8x 10^-3

deduce the rate equation and rate constant.

can someone please show me the complete working.

 

[sweetiepie]

http://www.xtremepapers.com/community/threads/some-different-notes-website-are-available.10423/ check these for notes hope this helps

 

[Silent Hunter]

One thing i need to ask:

that in A2 organic how much of the AS we need to know specifically or its like all ov it?