Chemistry: Post your doubts here!

[qwertypoiu]

When NH3(aq) is added to a green solution containing Ni2+(aq) ions, a grey-green precipitate is formed. This precipitate dissolves in an excess of NH3(aq) to give a blueviolet solution. Suggest an explanation for these observations, showing your reasoning and including equations for the reactions you describe.

The green ppt. is Ni(OH)2. How are we supposed to get that ?

This is similar to how Cu reacts with NH3.

On adding drops of NH3, it ionizes:

NH3 + H2O <---> NH4+ + OH-

The Ni2+ (aq) is in fact [Ni(H2O)6]2+ (aq). A ligand exchange reaction occurs upon addition of OH-:

[Ni(H2O)6]2+ (aq) + 2OH-(aq) <----> Ni(H2O)4(OH)2 (s) + 2H2O

The solid produced is the ppt. Sometimes we ignore the water ligands and simply write Ni(OH)2. Same thing applies for copper. Only the color differs.

When excess ammonia is added, more ligands are replaced, this time by molecular NH3:

Ni(H2O)4(OH)2 (s) + 4NH3(aq) ------> [Ni(NH3)4(H2O)2]2+ (aq) + 2H2O + 2OH- (aq)

 

[The Sarcastic Retard]

When NH3(aq) is added to a green solution containing Ni2+(aq) ions, a grey-green precipitate is formed. This precipitate dissolves in an excess of NH3(aq) to give a blueviolet solution. Suggest an explanation for these observations, showing your reasoning and including equations for the reactions you describe.

The green ppt. is Ni(OH)2. How are we supposed to get that ?

Colors of complexes.
Ni2+(aq) + NH3(aq) ------> Ni(OH)2 (precipitated form is x(OH)2 If u are asked to write about formula of precipiate it will have (OH)2 as ligand with some metal X) When u add excess of NH3 you will get Ni(H2O)2(NH3)4 which will give blue violet solution.

 

[The Sarcastic Retard]

Colors of complexes.
Ni2+(aq) + NH3(aq) ------> Ni(OH)2 (precipitated form is x(OH)2 If u are asked to write about formula of precipiate it will have (OH)2 as ligand with some metal X) When u add excess of NH3 you will get Ni(H2O)2(NH3)4 which will give blue violet solution.

qwertypoiu mine is correct?

 

[Rizwan Javed]

Can anyone tell me what will be the structural formula of the product, if CH3CH=CHCHO is reacted with H2 under nickel catalyst?

 

[qwertypoiu]

qwertypoiu mine is correct?

Yes sort of
It's based on what has been assumed. For example, saying:

Ni2+(aq) + NH3(aq) ------> Ni(OH)2

is a bit strange given there is NH3 on left side and suddenly OH- on right side. But of course, if the reader knows NH3 ionises to form OH- ions, then it may be fine. Also you said X(OH)2 for some metal X, again this is true if we assume X to be X2+ ion and not some other valency.

 

[The Sarcastic Retard]

Yes sort of
It's based on what has been assumed. For example, saying:

is a bit strange given there is NH3 on left side and suddenly OH- on right side. But of course, if the reader knows NH3 ionises to form OH- ions, then it may be fine. Also you said X(OH)2 for some metal X, again this is true if we assume X to be X2+ ion and not some other valency.

wuhhuuuuuuuuuuuu!! Bingo

 

[The Sarcastic Retard]

Can anyone tell me what will be the structural formula of the product, if CH3CH=CHCHO is reacted with H2 under nickel catalyst?

According to me its REduction and Hydrogenation takes place. CH3CH2CH2CH2OH

 

[qwertypoiu]

Can anyone tell me what will be the structural formula of the product, if CH3CH=CHCHO is reacted with H2 under nickel catalyst?

According to me its REduction and Hydrogenation takes place. CH3CH2CH2CH2OH

I think aldehyde group will also be reduced.
So
CH3CH2CH2CH2OH

Edit: Sorry The Sarcastic Retard I think you edited your answer

 

[The Sarcastic Retard]

I think aldehyde group will also be reduced.
So
CH3CH2CH2CH2OH

I just edited my post

 

[Rizwan Javed]

I think aldehyde group will also be reduced.
So
CH3CH2CH2CH2OH

Thanks. I didn't notice that the aldehyde group will also reduced.

 

[Rizwan Javed]

I just edited my post

Thanks

 

[The Sarcastic Retard]

Thanks. I didn't notice that the aldehyde group will also reduced.

It reduces due to addition of H2 (Addition of H2 causes reduction) *Phew*

 

[holoholo]

Yes sort of
It's based on what has been assumed. For example, saying:

is a bit strange given there is NH3 on left side and suddenly OH- on right side. But of course, if the reader knows NH3 ionises to form OH- ions, then it may be fine. Also you said X(OH)2 for some metal X, again this is true if we assume X to be X2+ ion and not some other valency.

So it is not (OH)2(H2O)4 ?

 

[The Sarcastic Retard]

Can anyone draw structure of Fe(EDTA)
qwertypoiu

 

[The Sarcastic Retard]

So it is not (OH)2(H2O)4 ?

It is that only...

 

[The Sarcastic Retard]

So it is not (OH)2(H2O)4 ?

It is that only...

 

[Lola_sweet]

1) explain, in terms of rates of the forward and reverse reactions, what is meant by a reversible reaction?
2) calculate the quantities present at equilibrium, given appropriate data (such calculations will not require the solving of quadratic equations)

anyone have notes for these points from the syllabus?

 

[qwertypoiu]

1) explain, in terms of rates of the forward and reverse reactions, what is meant by a reversible reaction?
2) calculate the quantities present at equilibrium, given appropriate data (such calculations will not require the solving of quadratic equations)

anyone have notes for these points from the syllabus?

You're looking for 7.1a and 7.1f

Hope the links are helpful

 

[qwertypoiu]

So it is not (OH)2(H2O)4 ?

Both refer to the same thing.

Ni(OH)2 is just a short form of what is technically more correct, Ni(H2O)4(OH)2

 

[qwertypoiu]

Can anyone draw structure of Fe(EDTA)
qwertypoiu

Sorry I've never heard of that