OCR B Salters - F335 Exam - 15 June 2011

Original post by tkoki1993

well that makes sense... how many marks was the question...
and while i'm talking about marks, anyone got THE PAPER?
please upload.... you'd get showered with pos rep if you do :biggrin:

I think it was a 1 mark question lol.

Reply 821

limetang

19

On a brighter note though. I think the general consensus is that it was a challenging paper. So the grade boundaries should reflect this so we 'should' be okay.

Reply 822

tkoki1993

OP

10

Original post by arsenalman

I think it was a 1 mark question lol.

I guess i've been reading into it a bit too much lool

Reply 823

Adam9

What did people get for why CH2BrCH2Cl and CH2BrCH2Br dissolve in eachother but not in water?

I said its coz hydrogen bonds between water molecules are stronger than the permanent dipole-permanent dipole bonds in the halogenoalkane molecules. This bonds between water molecules are stronger than the bonds that would form between water and halegenoalkanes, so the bonds do not form.

I hope that was right ... That paper was sooooooooooooooo HARD

Reply 824

smaks

I used a wavelength of 1030cm-1 or something like that because i thought that because it's a reciprocal then 1030>1700 because 1/1030>1/1700.
I'm probably wrong so rate if you agree...

Reply 825

smaks

Original post by Adam9

What did people get for why CH2BrCH2Cl and CH2BrCH2Br dissolve in eachother but not in water?

I said its coz hydrogen bonds between water molecules are stronger than the permanent dipole-permanent dipole bonds in the halogenoalkane molecules. This bonds between water molecules are stronger than the bonds that would form between water and halegenoalkanes, so the bonds do not form.

I hope that was right ... That paper was sooooooooooooooo HARD

Did the same, paper was really hard. hope the grade boundaries are like 30% for an A :P

Reply 826

smaks

Did anyone get the total entropy value as 10464?

Reply 827

cleverbong

Original post by smaks

Did anyone get the total entropy value as 10464?

No. I got +9979

Reply 828

cleverbong

Original post by Adam9

What did people get for why CH2BrCH2Cl and CH2BrCH2Br dissolve in eachother but not in water?

I said its coz hydrogen bonds between water molecules are stronger than the permanent dipole-permanent dipole bonds in the halogenoalkane molecules. This bonds between water molecules are stronger than the bonds that would form between water and halegenoalkanes, so the bonds do not form.

I hope that was right ... That paper was sooooooooooooooo HARD

I said the same as you and also instantaneous dipole - induced dipole in CH2BrCH2Cl and CH2BrCH2Br.

Reply 829

ABCDemily

2

Original post by cleverbong

I said the same as you and also instantaneous dipole - induced dipole in CH2BrCH2Cl and CH2BrCH2Br.

I think I did the same as this! I definitely mentioned water forms h bonds and all that, so I've hopefully got half marks.

Reply 830

Mr.Messy

14

Original post by smaks

I used a wavelength of 1030cm-1 or something like that because i thought that because it's a reciprocal then 1030>1700 because 1/1030>1/1700.
I'm probably wrong so rate if you agree...

For the same bond of the 3 dye things?
I thought it said on the question it had to be above 1700cm-1 wavelength? So I just put the OH, 2500-27850cm-1 for a carboxylic acid.

Reply 831

Tetanus

Original post by Mr.Messy

For the same bond of the 3 dye things?
I thought it said on the question it had to be above 1700cm-1 wavelength? So I just put the OH, 2500-27850cm-1 for a carboxylic acid.

Same.

Reply 832

arsenalman

Original post by Mr.Messy

For the same bond of the 3 dye things?
I thought it said on the question it had to be above 1700cm-1 wavelength? So I just put the OH, 2500-27850cm-1 for a carboxylic acid.

yh thats what i did. But the wavelength for O-H carboxylic acids is 2500-3200.

(edited 12 years ago)

Reply 833

arsenalman

Original post by Adam9

What did people get for why CH2BrCH2Cl and CH2BrCH2Br dissolve in eachother but not in water?

I said its coz hydrogen bonds between water molecules are stronger than the permanent dipole-permanent dipole bonds in the halogenoalkane molecules. This bonds between water molecules are stronger than the bonds that would form between water and halegenoalkanes, so the bonds do not form.

I hope that was right ... That paper was sooooooooooooooo HARD

I said that it had permanent dipole-permanent dipole bonds and doesnt have hydrogen bonds so it cant dissolve in water. I said for hydrogen bonds you need a hydrogen bonded to nitrogen, flourine or oxygen and lone pair of electrons on them. And they have the same intermolecular bonding so they can dissolve in each other and form permanent dipole-induced dipole because the one with chlorine is more electronegative.

Reply 834

Willetts.Josh

Original post by tom108

Can anyone remember the question to the 4 marker calculation at the end ?

Hey, I think I remember what it was.

The value of Ka was 6.2x10^-8
And they used a concentration of 0.1 of A- (I can't remember the formula)
And you knew the pH was 7, so the conc of H+ ions was 10^-7

6.2x10^-8 = (10^-7 x 0.1)/[HA]

So the concentration of HA was 5/31 moldm-3

You only wanted 1dm^3 so there was 5/31 mols of it needed.
The Mr was 120, so 5/31 times 120 makes roughly 19.4g