Chemistry: Post your doubts here!

[Metanoia]

HpoView attachment 58624
How to find the value of atomisation of chlorine??

Look for the Bond energy data in the data booklet

Cl2 (g) --> 2Cl (g)

Divide that value by 2 to get the atomization of chlorine

1/2Cl(g) --> Cl (g)

 

[Metanoia]

View attachment 58623
c

CaMg(CO3)2 (s) --> CaO (s) + MgO (s) + 2CO2 (g)

Original Mr of CaMg(CO3)2 = 184

Mr "lost" = 2 x Mr of CO2 = 88

% lost in mass = (88/184) x 100%

 

[nehaoscar]

To show that the reaction is first order with respect to the reactant in the y-axis. Draw lines to figure out the half-lives (duration for a concentration to drop to half its value).

The convenient ones I've chosen for this question is the time taken to drop from 0.2 M to o.1M, and time taken to drop from 0.1 M to 0.05 M.

For 1st order, the durationsView attachment 58655 should be the same.

Thanks!
And what about the next part? - part 2.a.iii
How to find the order wrt HCl?

 

[Metanoia]

Thanks!
And what about the next part? - part 2.a.iii
How to find the order wrt HCl?

You will need both graphs for this.

Draw the tangents to both graphs at time = 0

For example..

If the gradient of tangent at double the concentration is TWICE the gradient of the other tangent; then its first order wrt to HCl.

 

[nehaoscar]

You will need both graphs for this.

Draw the tangents to both graphs at time = 0

For example..

If the gradient of tangent at double the concentration is TWICE the gradient of the other tangent; then its first order wrt to HCl.

Ok thanks!
can you give the formula for all orders using this method?
Like if it's twice then it's first order
then when is it zero and second order?

 

[My Name]

Hey guys,
Am an AS student! I am done with the inorganic part of the book (ch1-ch13), so today I will start with the organic part, everyone is freaking about organic chemistry, so can you advice me on how to study this part of the book, inorder to be able to score a high A in my AS?

Thanks in advance

I am sorry if I made you feel OC is tough. XD You'll do great.In sha Allah.
One thing is just even though it may feel hard just keep going.You'll get the hang of it eventually.
Be sure to keep revising the mechanism,conditions and reagents.Keep reading them over and over again.
Solve past paper with patience.

 

[My Name]

Hahahahha, its okay its not only you, everyone is in my school, even my teacher herself (she keeps on saying lets finish the syllabus fast as the organic chemistry is hard and will take a lot of time and efforts!)
Inshallah, I will try my best and thank you Umm how many days do you think it might take me to study all the 5 chapters?

Welcome.In sha Allah you'll do well.
I really can't say how much time it'll take.

 

[My Name]

Ohh, inshallah, how much time did it take you then?

I forgot. X(

 

[Metanoia]

Ok thanks!
can you give the formula for all orders using this method?
Like if it's twice then it's first order
then when is it zero and second order?

If its zero order, double the concentration will not affect the gradient , the graphs will overlap and be identical.

If its second order, doubling the concentration will have 4 times the gradient.

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_42.pdf
question 5. How do you solve this question and from what chapter is this from ?

If you are referring to part a), unfortunately, there isn't any (straightforward) rule to determine if the carbon atoms are co-planar or not.

It ultimately depends on if you able to visualize the shape in 3D format and picture the rotation of the single bonds to force the carbon atoms to line on the plane.

Only option B is not coplanar , the 2 carbon atoms on the right side are unable to lie on the same plan as the rest.

 

[holoholo]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_42.pdf
question 5. How do you solve this question and from what chapter is this from ?

 

[holoholo]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_42.pdf
question 5. How do you solve this question and from what chapter is this from ?

 

[holoholo]

Acidified solutions of iron(II) salts can be titrated using a dilute solution of potassium manganate(VII), KMnO4.
write a balanced ionic equation.
which equation should we use for MnO4- ions and why do we use this ?

 

[fleurisabelle]

Acidified solutions of iron(II) salts can be titrated using a dilute solution of potassium manganate(VII), KMnO4.
write a balanced ionic equation.
which equation should we use for MnO4- ions and why do we use this ?

half equation for iron: Fe 2+ >> Fe3+ + e-
half euation for MnO4 ions: MnO4- + 5e- + 8H+ >> Mn2+ + 4H2O
we multiply the first half-equation by 5 so that the electrons will cancel:
5Fe^2+ >> 5Fe^3+ 5e-

Combining both we have:
MnO4- + 5Fe+ + 8H+ >> Mn2+ + 5Fe3+ + 4H2O
Check they charges now: they are 17 positive on both sides of the equation. Now add state symbols:
MnO4- (aq) + 5Fe+ (aq) + 8H+ (aq) >> Mn2+ (aq)+ 5Fe3+ (aq)+ 4H2O (l)

n there you go!
the 2nd half equation, it's very useful to just learn it

 

[holoholo]

in the data booklet there is another equation for MnO4- which is
MnO4- + 4H+ + 3e ---> MnO2 + 2H2O
why can't we use this one ?

 

[Metanoia]

in the data booklet there is another equation for MnO4- which is
MnO4- + 4H+ + 3e ---> MnO2 + 2H2O
why can't we use this one ?

That would be used in alkaline conditions.

 

[holoholo]

but it is H+ in the equation, isn't that acidic ?

 

[Metanoia]

but it is H+ in the equation, isn't that acidic ?

the H+ is for purpose of balancing the equation

MnO4- + 4H+ + 3e ---> MnO2 + 2H2O

If you really want reflect that it is non-acidic, you can manipulate the equation as follows.

MnO4- + 4H+ +4OH- + 3e ---> MnO2 + 2H2O + 4OH-

MnO4- + 4H2O + 3e ---> MnO2 + 2H2O + 4OH-

MnO4- + 2H2O + 3e ---> MnO2 + 4OH-

 

[holoholo]

how about with H2O2 ? there are two equations. when do you know which one to use ?

 

[holoholo]

Can you explain how this is nucleophilic substitution