You mods don't go merging my topic k, this is a doubt that I wanna settle :D
Chemistry 5072 Paper 2
To cut it short, will platinum atoms EVER form platinum ions in a normal situation (like not under 1000 atm and 3500 degrees celsius la...)?
Because there was an electroplating question. It was coating an iron cylinder (or smth like that) with aq zinc sulphate, and the iron is -ve charged. So zinc ions in solution go and reduced there form zinc right, then iron plated with zinc, ya simple to understand right ;D
They asked why do we need to replace zinc brushes more than platinum brushes. Because it's like electroplating, the zinc "rod" is called a brush here, whereby zinc atoms will go into the aq zinc sulphate solution, blah blah blah story...
So will platinum EVER be oxidised to platinum ions and go into the aq zinc sulphate?
It's like using a platinum and iron rod in electroplating, then the electrolyte is aq zinc sulphate.
I wrote, about the replacement thingy, "As zinc is more reactive metal than platinum, zinc atoms will lose electrons to form zinc ions MORE READILY than platinum atoms losing electrons to form platinum ions, thus the zinc brush will become thinner more quickly than platinum over time and not as efficient in apply aq zinc sulphate onto the iron plate."
Meh, too kanchiong, all concepts went out of the window liao... Should just write platinum is inert right... Btw the question is 2 marks.
Thanks for checking :D
EDIT: New doubt. A question wanted us to write the formula for the amide and ester linkages... So draw structural formula or write? And what is the formula?
Btw, they gave us the whole damn structural formula of nylon and terylene, so I think if they want you to draw the amide and ester linkages, a bit too give away liao lor...
Originally posted by Garrick_3658:You mods don't go merging my topic k, this is a doubt that I wanna settle :D
Chemistry 5072 Paper 2
To cut it short, will platinum atoms EVER form platinum ions in a normal situation (like not under 1000 atm and 3500 degrees celsius la...)?
Because there was an electroplating question. It was coating an iron cylinder (or smth like that) with aq zinc sulphate, and the iron is -ve charged. So zinc ions in solution go and reduced there form zinc right, then iron plated with zinc, ya simple to understand right ;D
They asked why do we need to replace zinc brushes more than platinum brushes. Because it's like electroplating, the zinc "rod" is called a brush here, whereby zinc atoms will go into the aq zinc sulphate solution, blah blah blah story...
So will platinum EVER be oxidised to platinum ions and go into the aq zinc sulphate?
It's like using a platinum and iron rod in electroplating, then the electrolyte is aq zinc sulphate.
I wrote, about the replacement thingy, "As zinc is more reactive metal than platinum, zinc atoms will gain electrons to form zinc ions MORE READILY than platinum atoms gaining electrons to form platinum ions, thus the zinc brush will become thinner over time and not as efficient in apply aq zinc sulphate onto the iron plate."
Meh, too kanchiong, all concepts went out of the window liao... Should just write platinum is inert right... Btw the question is 2 marks.
Thanks for checking :D
platinum electrodes will not dissolve into the solution to form platinum ions
zinc atoms should lose electrons to form zinc ions i thought?
Lol, paiseh, my bad, typo.
Wa, then my answer is half wrong liao lor...
I added another doubt.
Hmmm the platinum one, platinum is inert so I guess it's unreactive and H+ ions will be discharged at it instead..? As for zinc, it should lose electrons to form Zn2+ ions, right? >< Not too sure.. =/
By the way, why zinc coating [is it, can't really remember the question] don't need replacing even though it is damaged, is it because it is oxidised by the oxygen in the air to form a layer of zinc oxide, thus preventing further reaction? >< Sounds wrong ):
And yes, regarding that organic chemistry question -.-" they kept asking 'formula' which made me go "structural or what?" =[ So I just wrote out that linkage, since I guess that formula is still that structural formula?
what i wrote was, Plat is an inert electrode.
Zinc is a reactive electrode.
When you are plating, Zinc ions from the brush will replace the zinc ions that went into plating.
ya so the conc. of zinc ions will not change right?
Originally posted by Garrick_3658:You mods don't go merging my topic k, this is a doubt that I wanna settle :D
Chemistry 5072 Paper 2
To cut it short, will platinum atoms EVER form platinum ions in a normal situation (like not under 1000 atm and 3500 degrees celsius la...)?
Because there was an electroplating question. It was coating an iron cylinder (or smth like that) with aq zinc sulphate, and the iron is -ve charged. So zinc ions in solution go and reduced there form zinc right, then iron plated with zinc, ya simple to understand right ;D
They asked why do we need to replace zinc brushes more than platinum brushes. Because it's like electroplating, the zinc "rod" is called a brush here, whereby zinc atoms will go into the aq zinc sulphate solution, blah blah blah story...
So will platinum EVER be oxidised to platinum ions and go into the aq zinc sulphate?
It's like using a platinum and iron rod in electroplating, then the electrolyte is aq zinc sulphate.
I wrote, about the replacement thingy, "As zinc is more reactive metal than platinum, zinc atoms will lose electrons to form zinc ions MORE READILY than platinum atoms losing electrons to form platinum ions, thus the zinc brush will become thinner more quickly than platinum over time and not as efficient in apply aq zinc sulphate onto the iron plate."
Meh, too kanchiong, all concepts went out of the window liao... Should just write platinum is inert right... Btw the question is 2 marks.
Thanks for checking :D
EDIT: New doubt. A question wanted us to write the formula for the amide and ester linkages... So draw structural formula or write? And what is the formula?
Btw, they gave us the whole damn structural formula of nylon and terylene, so I think if they want you to draw the amide and ester linkages, a bit too give away liao lor...
The zinc brush contains the zinc ions which dissolve when the electroplating is conducted. The zinc ions replace the zinc ions from the aq zinc sulphate solution hence effective concentration remains the same.
As the zinc brush loses zinc ions, it shrinks in size gradually. Thus the brush needs to be replaced.
how come this years paper so ez?!?!
Originally posted by iamapebble:Hmmm the platinum one, platinum is inert so I guess it's unreactive and H+ ions will be discharged at it instead..? As for zinc, it should lose electrons to form Zn2+ ions, right? >< Not too sure.. =/
By the way, why zinc coating [is it, can't really remember the question] don't need replacing even though it is damaged, is it because it is oxidised by the oxygen in the air to form a layer of zinc oxide, thus preventing further reaction? >< Sounds wrong ):
And yes, regarding that organic chemistry question -.-" they kept asking 'formula' which made me go "structural or what?" =[ So I just wrote out that linkage, since I guess that formula is still that structural formula?
Ok fine, so platinum is inert. But why "replace less often"? Why cannot use FOREVER. Inert what. Explain please.
The zinc coating thing is because zinc is a more reactive metal, thus acts as a sacrificial metal to prevent iron from rusting ;)
They want your write structural nia meh, so give away ahh.
I am gonna wait for tintin or UltimaOnline or eagle to give their comments. Typing their names always summons them :D
structural formula means to draw it out. It is not stuffs like CH3COOH. I am quite very sure.
EDIT: New doubt. A question wanted us to write the formula for the amide and ester linkages... So draw structural formula or write? And what is the formula?
Btw, they gave us the whole damn structural formula of nylon and terylene, so I think if they want you to draw the amide and ester linkages, a bit too give away liao lor..
I did either so no idea lol. The paper was so blardy easy that one small mistake will cost you alot alot. A1 cut off is 95% lol.
Originally posted by davidche:
I did either so no idea lol. The paper was so blardy easy that one small mistake will cost you alot alot. A1 cut off is 95% lol.
how u noe?
Garrick, regarding the platinum electrode issue, I'd rather read the actual question before commenting. But offhand, I'd say as far as this question and the 'O' level candidate is concerned, it really doesn't matter whether the platinum electrode needs to be replaced after a long time or never needs replacing. It's just the phrasing of the question that makes you unnecessarily worried. You'd probably get the full marks with your answer, and so will everyone else who wrote platinum is "inert".
As for the structural formula issue. I've told everyone here many times already, whenever you're in doubt as to exactly what the question wants, GIVE ALL POSSIBLE ANSWERS, AS LONG AS ALL THESE ANSWERS ARE ALL CORRECT (AND AS LONG AS YOU QUALIFY YOUR ANSWERS). In this context, the smart thing to do (if you're not sure which they want) would be to have drawn out BOTH the full structural formula, AND written the condensed formula, but qualify/label both correctly. Like this :
Full structural formula :
| |
C=O C=O
| |
H-N O
| |
Condensed formula :
-CONH- -COO-
While it is possible that the mark scheme and examiner, will accept both the drawing (structural formula) form and the written (condensed formula) form; although to be honest, if the question asks for "write out the STRUCTURAL formula", it means they want you to DRAW out ALL the bonds and atoms (instead of writing the condensed formula). You may not get any marks if you only wrote the condensed formula form.
I wrote both, but I ain't sure of my condensed formula answer. Because I had never wrote the condensed formula before. And so I just follow suit and copied what's on the structural formula. Like this:
Amide: OCNH (lol looks weird)
Ester: OCO (more weirdness)
So, is this acceptable? I doubt so right...
And crap, I forgot those extra linkage lines that aren't bonded to anything...
Anyway, thanks to everyone that helped!
A1 cut off is 95% lol.
Who say one? Cambridge so fast marked finish liao ah? Paper 1 not even over yet...
cos paper ish kinda easy.