The Student Room Group

Edexcel IAL, Unit 5: Transition Metals and Organic Nitrogen Chemistry. 22-Jun-2016

Scroll to see replies

image.jpgIsn't it supposed to be C?
Original post by Quirky01
image.jpgIsn't it supposed to be C?


The answer is D because in the hydrogen half cell, electrons are lost by hydrogen i.e hydrogen gets oxidised. Another reason is that if you compare the values for the half cell of oxygen and hydrogen, oxygen has a positive value so when the value is positive, we say that the species will be reduced as electrons will arrive at this electrode because the forward reaction i.e
O2+H20+4e--->4OH- is favored.
(edited 7 years ago)
Hey! I wanted to ask that in an electrochemical cell, we use a salt bridge with a fliter paper soaked in potassium nitrate right? So why do we actually soak it in potassium nitrate? Is it something to do with the ions travelling?
Can anyone plx tell why hydrogen halides are soluble in water. Like for something to be soluble in water it must be polar, ok i get HF is polar so dissolves, same with HCl and HBr but HI and HAt are non polar i believe so why are they still soluble?
All potassium salts and nitrates are soluble. So they won't react with any of the ions in the half cells to produce precipitates
Original post by munzariiiin
All potassium salts and nitrates are soluble. So they won't react with any of the ions in the half cells to produce precipitates


Thanks! :smile:
Hey would really appreciate it if someone could explain these two questions to me? Thanks!

This one, I thought The sulfur in SO2 is oxidised and the O2 reduced? Therefore I was under the impression that sulfur "gives" it's electron to the vanadium (V) oxide catalyst, hence making it vanadium (VI), then back to vanadium (V) by oxygen. However, the answer is D - not so sure why.




With this question, I had thought that when you add small amounts of NaOH and Ammonia to a sample, you get a precipitate (in a deprotonation reaction) before the ligands are actually displaced on adding excess. Therefore I put D, both as ligand exchange as it seemed from the question that the precipitates dissolved. However, the answer is B. Would really appreciate your explanations! thanks!


(edited 7 years ago)
Original post by gabby07
Hey would really appreciate it if someone could explain these two questions to me? Thanks!

This one, I thought The sulfur in SO2 is oxidised and the O2 reduced? Therefore I was under the impression that sulfur "gives" it's electron to the vanadium (V) oxide catalyst, hence making it vanadium (VI), then back to vanadium (V) by oxygen. However, the answer is D - not so sure why.




With this question, I had thought that when you add small amounts of NaOH and Ammonia to a sample, you get a precipitate (in a deprotonation reaction) before the ligands are actually displaced on adding excess. Therefore I put D, both as ligand exchange as it seemed from the question that the precipitates dissolved. However, the answer is B. Would really appreciate your explanations! thanks!




You are almost there- for the first one, your logic is completely correct but you are making a slight error - if the sulphur gives one electron to the vanadium 5+ then the charge and hence ox state of the vanadium is now +4, not +6. In the second question, your logic for ammonia is correct, it is the OH part that is wrong. In a ligand exchange reaction, the ligand attached to the cation is changed. However when we add excess OH all that is happening is that a proton from the h2o ligands are protonating the oh- ions forming water, leaving behind a oh attached to the cation rather than the oh coming from the sodium hydroxide, and hence it is not ligand exchange
Original post by samb1234
You are almost there- for the first one, your logic is completely correct but you are making a slight error - if the sulphur gives one electron to the vanadium 5+ then the charge and hence ox state of the vanadium is now +4, not +6. In the second question, your logic for ammonia is correct, it is the OH part that is wrong. In a ligand exchange reaction, the ligand attached to the cation is changed. However when we add excess OH all that is happening is that a proton from the h2o ligands are protonating the oh- ions forming water, leaving behind a oh attached to the cation rather than the oh coming from the sodium hydroxide, and hence it is not ligand exchange


Thank you so much! so does this mean that whenever you add excess NaOH to a transition metal, it is never ligand exchange? it's always deprotonation?
Original post by gabby07
Thank you so much! so does this mean that whenever you add excess NaOH to a transition metal, it is never ligand exchange? it's always deprotonation?


Yes. It's also a good idea to know that chromium 3 compounds are often amphoteric
Reply 110
Original post by gabby07
Hey would really appreciate it if someone could explain these two questions to me? Thanks!

This one, I thought The sulfur in SO2 is oxidised and the O2 reduced? Therefore I was under the impression that sulfur "gives" it's electron to the vanadium (V) oxide catalyst, hence making it vanadium (VI), then back to vanadium (V) by oxygen. However, the answer is D - not so sure why.




With this question, I had thought that when you add small amounts of NaOH and Ammonia to a sample, you get a precipitate (in a deprotonation reaction) before the ligands are actually displaced on adding excess. Therefore I put D, both as ligand exchange as it seemed from the question that the precipitates dissolved. However, the answer is B. Would really appreciate your explanations! thanks!




So, with first question, it's like we know vanadium has four oxidation states (+2, +3, +4 and +5) and it shows A and B are not possible (not sure about C and D)
And about second ligand exchange exchange occurs in excess ammonia and as far as NaOH test is there it runs on basis of being amphoteric, idk why exactly but my chem teacher told me this for chem unit 6 when we read that only cr, zn and Al dissolve in excess NaOH as they're amphoteric and Cu, Cr and Zn dissolve in excess NH3 as they do ligand exchange!

Spoiler

Original post by samb1234
Yes. It's also a good idea to know that chromium 3 compounds are often amphoteric


Two quick questions.

Firstly, if we had little amount of NH3 to complex ion, it forms the ppt and thus is this not a ligand exchange reaction?

Secondly, is water and hydroxide ion (OH-) ligand essentially the same but the only difference is one is de-protonated?
Original post by popo111
Two quick questions.

Firstly, if we had little amount of NH3 to complex ion, it forms the ppt and thus is this not a ligand exchange reaction?

Secondly, is water and hydroxide ion (OH-) ligand essentially the same but the only difference is one is de-protonated?


If you add a small amount of ammonnia, the ammonia acts as a base, and accepts a hydrogen from some of the water ligands to form NH4+, so you get 3 waters deprotonating to OH. Yes essentailly they are the same ligand - for reaction with hydroxide ions throughout the entire process the same 6 oxygen atoms (or whatever number it may be, doesn't have to be 6) are coordinately bonded to the cation, only thing that changes is what else is attached to that oxygen if that makes sense
Original post by PlayerBB
Yeah, that would be great!! And thank you :h:


Original post by sabahshahed294
Yes that would be helpful! Thank you! :smile:


Original post by Aimen.
Oh please, do that! That'd be SO KIND of you! :smile:


Oh, dear. I never got notified on my phone about the replies so I completely missed this. I just checked and since the exams are on the 14th for Unit 4 (correct me if I'm wrong...), I'll try to get at least some notes out by then. I don't know if I'll be able to cover everything but I'll try. :smile:
Original post by PlayerBB
.


Original post by sabahshahed294
.


Original post by Aimen.
.


https://drive.google.com/folderview?id=0BwBWX8dVcLhpZjV3SG9nNTZOVnc&usp=sharing

I will be updating any Unit 4 notes in this folder. Currently, I have only made notes on the Introduction to Rates and Mechanisms in Unit 4. I will update with methods of measuring rates, experimental and graphical methods of determining rates, basic rate calculations, some short notes on catalysts and some experiments.

Which topics would you like me to prioritise after the rates notes?

Also, if there are any mistakes in the notes, please do let me know so I can correct them. :smile:
Original post by thymolphthalein
https://drive.google.com/folderview?id=0BwBWX8dVcLhpZjV3SG9nNTZOVnc&usp=sharing

I will be updating any Unit 4 notes in this folder. Currently, I have only made notes on the Introduction to Rates and Mechanisms in Unit 4. I will update with methods of measuring rates, experimental and graphical methods of determining rates, basic rate calculations, some short notes on catalysts and some experiments.

Which topics would you like me to prioritise after the rates notes?

Also, if there are any mistakes in the notes, please do let me know so I can correct them. :smile:


Thank you so much for your efforts!!

I don't know about the others but anything about NMR and infrared spectroscopy would be great!
(edited 7 years ago)
Original post by thymolphthalein
https://drive.google.com/folderview?id=0BwBWX8dVcLhpZjV3SG9nNTZOVnc&usp=sharing

I will be updating any Unit 4 notes in this folder. Currently, I have only made notes on the Introduction to Rates and Mechanisms in Unit 4. I will update with methods of measuring rates, experimental and graphical methods of determining rates, basic rate calculations, some short notes on catalysts and some experiments.

Which topics would you like me to prioritise after the rates notes?

Also, if there are any mistakes in the notes, please do let me know so I can correct them. :smile:


Thank you for your time. I guess NMR, pH Titration Curves and Buffers would be good enough. :smile:
Reply 117
Original post by thymolphthalein
https://drive.google.com/folderview?id=0BwBWX8dVcLhpZjV3SG9nNTZOVnc&usp=sharing

I will be updating any Unit 4 notes in this folder. Currently, I have only made notes on the Introduction to Rates and Mechanisms in Unit 4. I will update with methods of measuring rates, experimental and graphical methods of determining rates, basic rate calculations, some short notes on catalysts and some experiments.

Which topics would you like me to prioritise after the rates notes?

Also, if there are any mistakes in the notes, please do let me know so I can correct them. :smile:


Do the aldehydes, ketones and carboxylic acids please? ^^
Original post by sabahshahed294
Thank you for your time. I guess NMR, pH Titration Curves and Buffers would be good enough. :smile:


Original post by PlayerBB
Thank you so much for your efforts!!

I don't know about the others but anything about NMR and infrared spectroscopy would be great!


IR and NMR notes are up, please check and let me know if there are any errors. :smile:

https://drive.google.com/open?id=0BwBWX8dVcLhpZjV3SG9nNTZOVnc
Original post by Aimen.
Do the aldehydes, ketones and carboxylic acids please? ^^


I will try. Since organics cover a lot of content, I may not be able to do all three. I'll try to get aldehydes and ketones done if possible. :smile:

Quick Reply