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X is a dipeptide (when two monomers of amino acid join together). It is refluxed so that it can be hydrolysed to form 2 amino acid. HCL acts as a catalyst :smile:
hii can anyone explain the last part of the titration q in jan 2013? to get the percentage of the ascorbic acid why do they divide it by 2?????
Reply 1762
Can someone please explain 15d for me please? June 2012. Need I say, Unit 5? :wink:

Looking at the summary for that reaction, I would say the answer is Potassium permanganate, in acid solution. I don't know where the mark scheme has got: "Sodium Hydroxide and a Manganese salt" from?

Thanks!
Reply 1763
Hey guys what would be the systematic name of paracetamol? Perhaps n phenol ethanamide
Reply 1764
Original post by Inspire12
hii can anyone explain the last part of the titration q in jan 2013? to get the percentage of the ascorbic acid why do they divide it by 2?????


0.5g x 4 = 2
Original post by Dolphino
Hey guys what would be the systematic name of paracetamol? Perhaps n phenol ethanamide


yeah it is phenyl ethanamide
Is Manganese in the +7 oxidation state violet or colourless?
Reply 1767
Original post by Hellz_Bellz!
I keep getting As in the past papers I'm doing... but the real thing is always so much harder than the past ones :cry2:

By the way, do we need to know all the reactions from AS? Like how to convert alkenes to halogenoalkanes and all that crap?


We need to know everything it's Synoptics so Any reaction can creep up on the sly


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Reply 1768
Original post by AtomicMan
Is Manganese in the +7 oxidation state violet or colourless?


Violet. It's colourless in +2 state
Reply 1769
Original post by AtomicMan
Is Manganese in the +7 oxidation state violet or colourless?


Violet. eg KMnO4 - purple. Mn 2+ is colourless (although pale pink in concentrated solution)
Reply 1770
Can someone please please explain Q16 Jan 2012! How is Br2 acidic?!
Reply 1771
Original post by Inspire12
hii can anyone explain the last part of the titration q in jan 2013? to get the percentage of the ascorbic acid why do they divide it by 2?????


15 iii) or 15iv)



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Original post by bubblegummer
X is a dipeptide (when two monomers of amino acid join together). It is refluxed so that it can be hydrolysed to form 2 amino acid. HCL acts as a catalyst :smile:


Ohhh okay, thank you! I thought polypeptides were hydrolysed by dilute acid... hmmm. Can they be hydrolysed with alkali or not? :smile:
how to balance reactions in fuel cells
Original post by LeaX
Do you know if that is the only method of separation that we'll need to know about? If not, do we still follow those steps for any separation or does it differ depending on the mixture we're trying to separate? My book doesn't mention any of this. :frown:


Hey sorry for late reply, basically, in the exam I am hoping they will give context, so it will be much easier to see what they want, but there are normally two methods of extraction, depending on whether it is stable or unstable. In the case of being unstable organic, you must use steam distillation, followed by the standard drying procedure i.e. run of aqueous layer and add anhydrous salts. Other wise, if its stable, you can just distill it off, or if you know it is far more soluble in a certain solvent, whereas other substances in the same solution won't be, then you can use solvent extraction.
Hope this makes sense? x
Original post by sounique
Can someone please explain 15d for me please? June 2012. Need I say, Unit 5? :wink:

Looking at the summary for that reaction, I would say the answer is Potassium permanganate, in acid solution. I don't know where the mark scheme has got: "Sodium Hydroxide and a Manganese salt" from?

Thanks!


Basically, any manganese salt in solution will form a complex ion with water ligands. Then if you add sodium hydroxide or even ammonia (any base) it will deprotonate it to the corresponding manganese hydroxide for which its solid (neutral complex) form can be written as Mn(OH)2 or Mn(H20)4(OH)2

You don't need to refer to summary for this :smile:

Hope that makes sense
(edited 10 years ago)
Reply 1776
Original post by Bubblezzzz
Basically, any manganese salt in solution will form a complex ion with water ligands. Then if you add sodium hydroxide or even ammonia (any base) it will deprotonate it to the corresponding manganese hydroxide for which its solid (neutral complex) form can be written as Mn(OH)2 or Mn(H20)4(OH)2

You don't need to refer to summary for this :smile:

Hope that makes sense


Perfect. Thanks.
Reply 1777
what is solvent extraction!??
Original post by Bubblezzzz
Hey sorry for late reply, basically, in the exam I am hoping they will give context, so it will be much easier to see what they want, but there are normally two methods of extraction, depending on whether it is stable or unstable. In the case of being unstable organic, you must use steam distillation, followed by the standard drying procedure i.e. run of aqueous layer and add anhydrous salts. Other wise, if its stable, you can just distill it off, or if you know it is far more soluble in a certain solvent, whereas other substances in the same solution won't be, then you can use solvent extraction.
Hope this makes sense? x


thank you but i'm having a really hard time understanding this topic. my book mentions absolutely nothing on this. it tells me how to separate solids (recrystalisation) but not liquids. how does separation differ for aqueous and organic liquids? what is solvent extraction?
Original post by sounique
Wait what?! I just thought that Cr H20 6 is green! As it's in an aqueous solution and therefore ligand exchange has taken place?!!

Thanks for the rest :smile:


Before ligand exchange has taken place it's violet, after/if it takes place it becomes green :smile:

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