Chemistry: Post your doubts here!

[Bishnu Dev]

Subtract the smaller one from the larger one.
The answer would be 1.32-(-0.37)

Is that always the case or CIE prefers this one? What if i connect the voltmeter other way around? The magnitude remains same but the sign changes.

 

[anastasia grey113]

Is that always the case or CIE prefers this one? What if i connect the voltmeter other way around? The magnitude remains same but the sign changes.

This is always the case. A negative value is never considered becuz that shows that the reaction is not feasible.
Usually the voltmeter is connected with + terminal on the higher electrode potential so just remember larger - smaller for all.

Don't use it for feasibilities. It has a different method. Don't confuse it with E of cell.

 

[Bishnu Dev]

This is always the case. A negative value is never considered becuz that shows that the reaction is not feasible.
Usually the voltmeter is connected with + terminal on the higher electrode potential so just remember larger - smaller for all.

Don't use it for feasibilities. It has a different method. Don't confuse it with E of cell.

Well, group IV chlorides are removed from the syllabus, right? I have not done the recent papers but it appears frequently in test papers which were administered before 2016

 

[anastasia grey113]

Well, group IV chlorides are removed from the syllabus, right? I have not done the recent papers but it appears frequently in test papers which were administered before 2016

yes whole of group IV is out of syllabus

 

[Bishnu Dev]

Please explain b)

 

[Sheraz ali]

Iron(III) chloride, FeCl 3, is used to dissolve unwanted copper from printed circuit boards
(PCBs) by the following reaction.
2FeCl 3(aq) + Cu(s) → 2FeCl 2(aq) + CuCl 2(aq)
A solution in which [Fe3+(aq)] was originally equal to 1.50 mol dm–3 was re-used several
times to dissolve copper from the PCBs, and was then titrated as follows.
A 2.50 cm3
sample of the partially-used-up solution was acidifi ed and titrated with
0.0200 mol dm–3 KMnO4.
This oxidised any FeCl 2 in the solution back to FeCl 3.
It was found that 15.0 cm3
How one know that which MnO-4 half equation use

MnO4– + 4H++ 3e– MnO2 + 2H2O +1.67
MnO4– + 8H++ 5e– Mn2+ + 4H2O +1.52

 

[Sheraz ali]

How one know that which MnO-4 half equation use

MnO4– + 4H++ 3e– MnO2 + 2H2O +1.67
MnO4– + 8H++ 5e– Mn2+ + 4H2O +1.52

 

[Hamnah Zahoor]

View attachment 64308View attachment 64309
Can anybody help . Nov/17/p42 question 3.
Why has the NH not reacted ?
View attachment 64310
As seen on the marking scheme

It just simply does not react with bromine 'No reaction occurs'.
Here the question is basically focusing on where the the bromine will attach what will be the specified position which in this case are 2 & 6 as -OH is electron donating group.

 

[hamadh]

How many stereoisomers does piperic acid have? I mean the answer is 4 but i actually drew 8 of them and they are all different in terms of spatial arrangement. I hope you understand the spatial crisis here. I would be grateful if somebody could explain it to me.

 

[hamadh]

It just simply does not react with bromine 'No reaction occurs'.
Here the question is basically focusing on where the the bromine will attach what will be the specified position which in this case are 2 & 6 as -OH is electron donating group.

why does br2 not react with the double bond?

 

[hamadh]

Q3)b)
i) Why does Br2 not react with the double bond?
ii)why does ethyol chloride not react with N in the ring ?

 

[Hamnah Zahoor]

why does br2 not react with the double bond?

CCl4 is used as a solvent for electrophillic addition to occur with bromine But as seen in the question the bromine is in aqueous form thus it will not react with the double bond.

 

[hamadh]

View attachment 64313
CCl4 is used as a solvent for electrophillic addition to occur with bromine But as seen in the question the bromine is in aqueous form thus it will not react with the double bond.

Thank you so much!!

 

[Hamnah Zahoor]

Thank you so much!!

You are welcome

 

[Horsey]

Hey can some one help with the concept of tetrahedral and square planer complex? How to differentiate between the two?
Also this question, how do we know which equation from databooklet to use for Fe3 : 1) Fe3 + 3e- => Fe or 2) Fe3 + e- => Fe2

 

[Hamnah Zahoor]

Hey can some one help with the concept of tetrahedral and square planer complex? How to differentiate between the two?
Also this question, how do we know which equation from databooklet to use for Fe3 : 1) Fe3 + 3e- => Fe or 2) Fe3 + e- => Fe2

For your first question,
you will not have to be able to tell the difference between square planar and tetrahedral just based on the formula. However, if there is a name of a coordination complex with four ligands and cis- or trans- is specified, then you know that the complex must be square planar because all positions on a tetrahedral complex are equivalent. If neither cis- or trans- is specified, the compound may be either square planar or tetrahedral and you will not need to know the difference.

And also it mentions in the syllabus Tetrahedral OR square planar complex I think it is considered the same.

 

[Hamnah Zahoor]

 

[Horsey]

View attachment 64327

Thankyou so much Hamnah
Can you tell the name of shape and structure of Ni(CN)2(NH3)2 ?

 

[Hamnah Zahoor]

Thankyou so much Hamnah
Can you tell the name of shape and structure of Ni(CN)2(NH3)2 ?

 

[Horsey]

View attachment 64329

Oh thanks