Chemistry: Post your doubts here!

[itallion stallion]

Guys! Need help! For the 3rd one, why is it no reaction? Isn't it carboxylic acid + alcohol reaction?

Phenols will always react with acyl chloride to make esters not with alcohols.so there will be no reaction.

 

[Jinosupreme]

Can u plz show alpha helix also!

I think this is a good image for alpha helix

 

[goodluckayesha]

Thanks a lot!

ill upload for alpha-helix also

I think this is a good image for alpha helix

this is a lil complicated my book has an easy one ill upload it soon

 

[itallion stallion]

Plz help me with these questions
May June 2006 paper 4
Q4 diii
Q4 e(if I join tyrosine- lysine-glycine,will it also be fine)
Q5 part a reaction 1,I am confused when do we add only HNO3 and when add both HNO3 and H2SO4.
Thanks alot!

 

[itallion stallion]

ill upload for alpha-helix also

this is a lil complicated my book has an easy one ill upload it soon

Thanks a lot.

 

[itallion stallion]

I think this is a good image for alpha helix

I hope it never comes in exam!

 

[Haya Ahmed]

34:

I'd go with B. 3 is definitely wrong because calcium IONS wont react with H+, but solid will. 1 and 2 are correct. 2 is most definitely correct, and so I'm left with B.

35:
1- It does.
2- It does.
3- It doesn't because it's basic itself.

so, A

36:
B?

1- It is. NaClO3.
2- It does. +5 in NaClO3 and -1*5 in 5NaCl.
3- It doesn't. It's going from 6*+1 to +1 and 5*+1 so definitely not [R].

Thanks too much ^_^

 

[goodluckayesha]

Plz help me with these questions
May June 2006 paper 4
Q4 diii
Q4 e(if I join tyrosine- lysine-glycine,will it also be fine)
Q5 part a reaction 1,I am confused when do we add only HNO3 and when add both HNO3 and H2SO4.
Thanks alot!

in 4e u can join the amino acids in any order but there should be 3 amino acids present and 2 peptide bonds present
hmmm we use only dilute HNO3 when theres reaction with a phenol and H2SO4 and HNO3 when theres benzene or whtever got it?

 

[goodluckayesha]

I hope it never comes in exam!

its too easy give me 15 mins ill upload it

 

[NaNinG]

http://www.sheir.org/a-level-chemistry-51-nov2010.pdf
Q 2 (c)
y axis-----> Freezing point
x axis------> Molality of G

Can some1 please suggest which sequence of range of number do we asign for Y axis (especially) n X axis.
really get stuck here ;/

 

[goodluckayesha]

I hope it never comes in exam!

the first one is complicated but the second one has to be drawn in the exam n its quite simple i belief wht do u think?

 

[Haya Ahmed]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s06_qp_1.pdf


Question - 1 , 5 , 6

 

[sumeru]

Need help! why is the product at anode for MgBr is Br2? Isn't it suppose to be oxygen?

the half equation will be .....02+2H2O+4e=4OH.....and Br2+2e=2Br.....and if u look the E values.......OH- has greater tendency to get oxidised.......Remember this OH- comes from the dissociation of H2O present in the solution

 

[sitooon]

the half equation will be .....02+2H2O+4e=4OH.....and Br2+2e=2Br.....and if u look the E values.......OH- has greater tendency to get oxidised.......Remember this OH- comes from the dissociation of H2O present in the solution

Can you elaborate the point ? or compare it with the other two ? For cathode > more positive E vlaue will go to cathode and no doubt in that ..
What about anode?

 

[sumeru]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_42.pdf

Anyone generous to help
Q2 part b

 

[sumeru]

Can you elaborate the point ? or compare it with the other two ? For cathode > more positive E vlaue will go to cathode and no doubt in that ..
What about anode?

Ok....for cathode the two candidates are Mg2+ and H+ and according to E values ...H+ has more tendency to get reduced ....and for anode....at anode,oxidation occurs...so,the candidates are OH- and Br-....now, for cathode, if E values is positive, than that elements will get reduced.....and for anode, those elements having negative E vales will get oxidised.........

 

[periyasamy]

Hi guys,want to ask smthg.
How do i see which is identical.All seems same for me.Haha
The answer is j

 

[periyasamy]

Hei guys.Can anyone help me with this terribly hard question from may june 13 paper.Thank u.
My doubts r the last 3 reaction.
a)how can the 6th rxn be a ligand exchange
b)how can the last rxn show a ligand exchange n no acid base.Isnt there suppose to be acid base when got prescence of water as product.Thanks a lot.....

 

[sitooon]

Ok....for cathode the two candidates are Mg2+ and H+ and according to E values ...H+ has more tendency to get reduced ....and for anode....at anode,oxidation occurs...so,the candidates are OH- and Br-....now, for cathode, if E values is positive, than that elements will get reduced.....and for anode, those elements having negative E vales will get oxidised.........

02+2H2O+4e=4OH- E value is +0.40V
Br2+2e=2Br E value is + 1.07V

OH has lower ( more negative ) Evalue , so it will be at anode ???????

 

[sumeru]

OH- oxidises to give O2........you must be knowing that metals goes to cathode and non metal to anode......and at anode, oxidation takes place....and according to our E values, less positive have more tendency to get oxidised...