Chemistry: Post your doubts here!

[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

 

[fleurisabelle]

Can you explain how this is nucleophilic substitution View attachment 58706

Are you done with the whole syllabus? Actually, I've covered almost whole AS Chemistry but this question is still out of my comprehension. As far as I know, nucleophilic substitution involves halogenalkanes. Since all the halogens are more electronegative than carbon (with the exception of iodine), the electrons are pulled more by the halogens than by the carbon, which leaves the carbon a slightly positive charge while the halogen with a slightly negative charge. Now, the carbon is susceptible to attacks by nucleophiles and attaches with any nucleophile that comes in it's way. Looking at the list of common nucleophiles, NH2 is the one that could be involved here, but the picture presented by the structures show that a hydrogen has been lost, which is positive and could not possibly have acted as a nucleophile! if you do understand, be kind enough to explain me too!

 

[The Sarcastic Retard]

Can you explain how this is nucleophilic substitution View attachment 58706

N has lonepair to donate, so this reaction can be NS. That's all.
Reagent with lone pair can attack that's what we learnt right?

 

[fleurisabelle]

How can I know by just looking at the skeletal formula whether it contains a CH group a CH2 or a CH3, like there in the image, if I've gotta write it's structural formula, what it's going to be? I know that one projecting above must be a CH3 but what about the other four?

 

[fleurisabelle]

N has lonepair to donate, so this reaction can be NS. That's all.
Reagent with lone pair can attack that's what we learnt right?

Do you mean to say that it's the acid that has gone under nucleophilic substitution? but aren't those bromoethanes that go into nucleophilic substitution?

 

[nehaoscar]

How can I know by just looking at the skeletal formula whether it contains a CH group a CH2 or a CH3, View attachment 58729 like there in the image, if I've gotta write it's structural formula, what it's going to be? I know that one projecting above must be a CH3 but what about the other four?

Remember this for skeletal formula
Where each line joins, there is a C
The C must have 4 bonds and if no other functional groups are shown on the diagram, then it will be bonded to H
In this example, i have shown you what if would be like if there was OH
Note: It's better to convert it to displayed first and then to structural until you are confident with the skeletal formula.

 

[fleurisabelle]

Remember this for skeletal formula
Where each line joins, there is a C
The C must have 4 bonds and if no other functional groups are shown on the diagram, then it will be bonded to H
In this example, i have shown you what if would be like if there was OH
Note: It's better to convert it to displayed first and then to structural until you are confident with the skeletal formula.
View attachment 58730

thank you...it pretty much explained