Chemistry: Post your doubts here!

[sumeru]

Thank you!

Just to make sure, could you justify why it is 3! for the first question and 3P2 for the second question? I mean, why not 3P3 for the second question? (since it also gives 6).

You are asked to make dipetide out of 3 amino acids......so in how many ways can you arrange 2 from 3..i.e 3p2.......

 

[Namehere]

I've done this question so I know what precedes the question. But, this is primarily why I dislike when sections of the question are cropped out and asked.

Look at the diagrams above the part you've posted. It has a benzene, a cyclohexane, a straight chain alkane (I think butane?) and a branched alkane. It's telling you that benzene and the straight alkane carbon atoms are coplaner while the branched + cyclic carbons are not. THIS concept is to be used here. You need to identify which of A, B, C, D and E have rings OR branching. If they do, they're not co-planer.

I believe apart from B, all others are co-planer.

C is coplaner because of the C-O-C linkage. O is on a different plane but since we need to consider C atoms, it's co-planer. All the C's are in the same plane in this. If you don't get why C is co-planer, ask me and I'll draw it out.

Why is Oxygen on a different plane? Sorry for asking so many (stupid) questions.

 

[AbbbbY]

Why is Oxygen on a different plane? Sorry for asking so many (stupid) questions.

Ummm.. See the wedges

It has something to do with the lonepair + hybridization but I can't quite explain it.

See this.

The red part is the Oxygen.

 

[sitooon]

1 b(vi)

 

[AbbbbY]

1 b(vi)

Could you ttell me your answer to v? Would save me the trouble of going through all the steps.

Edit: Nevermind. Done them all anyway.

Original Solution: Fe3+ = 1.5 in 1000 so 0.15 in 100
Solution after dissolving copper several times: Fe2+ = Answer to part v/10 =0.6/10 = 0.06

Remaining Fe3+ = 0.15 - 0.06 = 0.09

Fe3+ : Cu
2 : 1
0.09 => 0.045mol

0.045 mol = 0.045*63.5 = 2.86g

 

[sitooon]

Could you ttell me your answer to v? Would save me the trouble of going through all the steps.

Edit: Nevermind. Done them all anyway.

Original Solution: Fe3+ = 1.5 in 1000 so 0.15 in 100
Solution after dissolving copper several times: Fe2+ = Answer to part v/10 =0.6/10 = 0.06

Remaining Fe3+ = 0.15 - 0.06 = 0.09

Fe3+ : Cu
2 : 1
0.09 => 0.045mol

0.045 mol = 0.045*63.5 = 2.86g

[Fe2+] = 1.5 × 10–3 × 1000/2.5 = 0.6 (mol dm–3) ecf from (iv)
Your ans is right
I got stuck myself at this stage :
"
Original Solution: Fe3+ = 1.5 in 1000 so 0.15 in 100
Solution after dissolving copper several times: Fe2+ = Answer to part v/10 =0.6/10 = 0.06

Remaining Fe3+ = 0.15 - 0.06 = 0.09 "
If you can elaborate this point if possible as how you did it .

 

[AbbbbY]

[Fe2+] = 1.5 × 10–3 × 1000/2.5 = 0.6 (mol dm–3) ecf from (iv)
Your ans is right
I got stuck myself at this stage :
"
Original Solution: Fe3+ = 1.5 in 1000 so 0.15 in 100
Solution after dissolving copper several times: Fe2+ = Answer to part v/10 =0.6/10 = 0.06

Remaining Fe3+ = 0.15 - 0.06 = 0.09 "
If you can elaborate this point if possible as how you did it .

Original conc is 1.5 dm3

this means:

1.5 mols in 1000 cm3
so
0.15 mols in 100 cm3

Conc of Fe2+
0.6 mols in 1000 cm3
so
0.06 mols in 100cm3

 

[Haya Ahmed]

Hey ! .. Can someone help me here !
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w05_qp_1.pdf

Question 34,35,36

Thanks ^_^

 

[ahmed abdulla]

Paper 5 , http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_53.pdf

Question 2b(iii) ( moles )
Question 3 , how to Complete the table > no formulas are given

& Whats is the max. Volume a gas syringe can hold which we are supposed to label here ?

AbbbbY

 

[itallion stallion]

Can someone plz help me with this chemistry question. 9701 october November 2011 paper 41 q6 bii.
Thanks!

 

[goodluckayesha]

Can someone plz help me with this chemistry question. 9701 october November 2011 paper 41 q6 bii.
Thanks!

this is beta-pleated
you have to draw either an alpha-helix or beta-pleated and show the hydrogen bonding between them

 

[AbbbbY]

Hey ! .. Can someone help me here !
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_qp_1.pdf

Question 34,35,36

Thanks ^_^

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].

 

[AbbbbY]

this is beta-pleated

Umm since they're beta pleated sheets, shouldn't they be running in opposite directions. I.e, CO under NH

 

[goodluckayesha]

Umm since they're beta pleated sheets, shouldn't they be running in opposite directions. I.e, CO under NH

they r not in diff directions.... in beta pleated hydrogen bonds form btw diff polypeptide chains and the r diff polypeptide chains
this diagram is lso given in my TB

 

[Jinosupreme]

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

GUYS! Need help in paper 4!

Can someone explain question 1 Biv)
I have no clue how to calculate the rate, and dont understand the mark scheme. Pls thanks!

 

[mahabaloch]

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

Anyone generous to help
Q2 part b

 

[Jinosupreme]

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

 

[itallion stallion]

this is beta-pleated
you have to draw either an alpha-helix or beta-pleated and show the hydrogen bonding between them

Thanks a lot!

 

[Jinosupreme]

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

 

[itallion stallion]

Umm since they're beta pleated sheets, shouldn't they be running in opposite directions. I.e, CO under NH

this is beta-pleated
you have to draw either an alpha-helix or beta-pleated and show the hydrogen bonding between them

Can u plz show alpha helix also!