Chemistry: Post your doubts here!

[daredevil]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_4.pdf
Please help me with qn no. 7(d) - both parts. Looks simple but I can't figure it out.
daredevil or anyone else
Thanks

see there are total 7 monomers that make up this polypeptide do if ' O ' is an amino acid and ' - ' is a peptide bond:

O-O-O-O-O-O-O

soo there are six peptide bonds between these amino acids

ii) when 1 peptide bond is formed H2O is released right? so if there are 6 peptide bonds formed then it means that when these monomers will combine, 6H2O molecules will be released. what u have to do here is to add all the Mr of the monomers (remember to multiply the Mr of one monomer with the no of moles of this monomer shown in the eq) when added all the Mr ... u will subtract the Mr of 6 H2O molecules from this.

 

[itallion stallion]

they have SUBTRACTED the electrons .... showing that the ions will lose electrons.
get it??

ummm i don't get wat u r saying about the electrode potential.... uss ka to iss part mein koi kaam nahi tha

What if I right the electrons on right for anode reactions like I have been since olevel,will it be okay!thanks

 

[itallion stallion]

Oohh i get ur point now...

see they have given us the REDUCTION potential as -1.23 but in this cell O2 is being oxidised so it will be -1.23 instead....
so as 1.23 is larger it will be

1.23-(-0.83) instead ) got it?

I just can't digest it!
Look in the data booklet it is given O2+4Hplus +4electron=2H2O and it's electrode potential value is +1.23v.now as the question says production of O2 at anode,I will invert the eq and write and it's Eo will become -1.23v right,now cathode Eo is -0.83v.E0 cell should be then -0.83-(-1.23).
I don't know what's wrong with me but plz clear the confusion!thanks alot

 

[abruzzi]

see there are total 7 monomers that make up this polypeptide do if ' O ' is an amino acid and ' - ' is a peptide bond:

O-O-O-O-O-O-O

soo there are six peptide bonds between these amino acids

ii) when 1 peptide bond is formed H2O is released right? so if there are 6 peptide bonds formed then it means that when these monomers will combine, 6H2O molecules will be released. what u have to do here is to add all the Mr of the monomers (remember to multiply the Mr of one monomer with the no of moles of this monomer shown in the eq) when added all the Mr ... u will subtract the Mr of 6 H2O molecules from this.

Thank you for the great explanation

 

[daredevil]

What if I right the electrons on right for anode reactions like I have been since olevel,will it be okay!thanks

yeah... at least i think it will be fine.
bcz seriously how wud we know if the examiner will write them on the left or the right side. i wudve written it the more standard way : on the right side.

 

[daredevil]

I just can't digest it!
Look in the data booklet it is given O2+4Hplus +4electron=2H2O and it's electrode potential value is +1.23v.now as the question says production of O2 at anode,I will invert the eq and write and it's Eo will become -1.23v right,now cathode Eo is -0.83v.E0 cell should be then -0.83-(-1.23).
I don't know what's wrong with me but plz clear the confusion!thanks alot

okay now i'm confused O_O

Rutzaba A star syed1995
u guys ... any thots? :`)

 

[AbbbbY]

Why won't SO2 wont show up?

How do you test for SO2 gas? Why would it show up if you're never taught how to test for it -_-

Ok looks like I was mistaken. I just confirmed the CIE amendment to the syllabus for P3.

It was the Pb2+ ion that they've removed not SO2. So, K2Cr2O7 will very much be on the reagents bench and you'll have to test for it by soaking the white strips of filter paper. If it turns from orange to green, voila.

 

[AbbbbY]

yeah... at least i think it will be fine.
bcz seriously how wud we know if the examiner will write them on the left or the right side. i wudve written it the more standard way : on the right side.

In exam you're supposed to always electrons in terms of addition, not subtraction, even though examiners will often ask you in terms of electrons subtracted.

X + e -> X
never
X - e -> X

 

[Namehere]

In exam you're supposed to always electrons in terms of addition, not subtraction, even though examiners will often ask you in terms of electrons subtracted.

X + e -> X
never
X - e -> X

If what I understand is correct, there is no difference on writing an electron as being added (onto one side of the equation) or subtracted (from the other side of the equation), so any way will be correct in the exam.

 

[AbbbbY]

Does anyone here have any diagram of electrophoresis? I mean an easy one because Marking schemes shows 3D diagrams. Thank You Suchal Riaz AbbbbY Namehere

This is what I make.

 

[daredevil]

Does anyone here have any diagram of electrophoresis? I mean an easy one because Marking schemes shows 3D diagrams. Thank You Suchal Riaz AbbbbY Namehere

the one AbbbbY drew was good too but they have given the diagram for that apparatus in the application booklet too :

 

[Rutzaba]

okay now i'm confused O_O

Rutzaba A star syed1995
u guys ... any thots? :`)

dint have chem

 

[A star]

This is what I make.

this made me feel so much better that some one daws as much worse as I do

 

[itallion stallion]

In exam you're supposed to always electrons in terms of addition, not subtraction, even though examiners will often ask you in terms of electrons subtracted.

X + e -> X
never
X - e -> X

Can u plz solve the electrode potential posted above,there Is a confusion in it.thanks
Bro still waiting for the p5.

 

[AbbbbY]

this made me feel so much better that some one daws as much worse as I do

Hahahh. This is one of my better drawings

Always sucked at drawings and diagrams and always will. This is why I loathe P5. All my diagrams are so funny it's actually amusing lol

 

[A star]

Hahahh. This is one of my better drawing

Always sucked at drawings and diagrams and always will. This is why I loathe P5. All my diagrams are so funny it's actually amusing lol

haha my long lost brother/sister . same here XD

 

[Abdulaziz T]

Guys if the question says draw the structure in organic chemistry , do we draw structural, displayed or skeletal diagrams ??

 

[Farez]

Guys if the question says draw the structure in organic chemistry , do we draw structural, displayed or skeletal diagrams ??

Unless they specifically ask for a particular structure diagram, any correct representation of the structure will be accepted.

 

[Abdulaziz T]

Unless they specifically ask for a particular structure diagram, any correct representation of the structure will be accepted.

Thanks a lot

 

[hope4thebest]

This is what I make.

Thank You so much! But once I made a similar diagram and my teacher pointed out that this is close to electrolysis, draw it as it is in marking scheme