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OCR Salters Chemistry F335 12th June 2013 Exam revision thread

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Original post by martynsteel
Right I think I've eventually got it, I reckons its due to the fact that we're told 1/3 of the solution is diluted, and the ratio of [salt]/[acid] HAS to be 2 (from reverse engineering the answer).

So my final calculating came to be:

(0.0045*0.1)/((2/3)*0.05*0.027) which works out to be 1/2 exactly. I think the trick of this question is that the concentration of the acid (HA) has been partially diluted. :smile:


thank you!
Original post by Kreayshawn
thank you!


You're welcome! :biggrin:
Reply 162
Avatar for super121
super121
5
Can someone please help me with Q2d on June 2010?
Why id-id bonds but not hydrogen bonds since both can form hydrogen bonds?
Thanks :smile:
Reply 163
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Reyoru
1
Original post by super121
Can someone please help me with Q2d on June 2010?
Why id-id bonds but not hydrogen bonds since both can form hydrogen bonds?
Thanks :smile:


They both have the ability to form two hydrogen bonds (two lones pairs on each oxygen) per molecule so talking about hydrogen bond strength seems redundant in this case. All compounds exhibit ID-ID (some experience additional bonding on top of this) and one compound is more branched so it makes more sense to talk about ID-ID forces here.
Reply 164
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super121
5
Original post by AmirHabeeb
They both have the ability to form two hydrogen bonds (two lones pairs on each oxygen) per molecule so talking about hydrogen bond strength seems redundant in this case. All compounds exhibit ID-ID (some experience additional bonding on top of this) and one compound is more branched so it makes more sense to talk about ID-ID forces here.


But one's more branched than the other, so surely you can say that it forms weaker intermolecular bonds because the chains cannot get as close together?
Do we need to know about partial pressure calculations? (Kp)
It's in my CGP revision guide but don't think I've seen it show up in any past papers and I can't see it on the specification
(edited 10 years ago)
Reply 166
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super121
5
Original post by Kreayshawn
Do we need to know about partial pressure calculations? (Kp)
It's in my CGP revision guide but don't think I've seen it show up in any past papers and I can't see it on the specification


Page 174 in chemical ideas says 'In this course, we do not deal quantitively with Kp'
Can someone please explain to me how to work out how many hydrogen environments there are in a compound in NMR?

When explaining, examples would be most appreciated.

Thank you 😃


Posted from TSR Mobile
Original post by super121
Page 174 in chemical ideas says 'In this course, we do not deal quantitively with Kp'


thanks!
hope there isn't too much else in this CGP guide that I might end up learning unnecessarily..

Is an ion-dipole bond the same thing as an ion-permanent dipole bond?
(edited 10 years ago)
Original post by Kreayshawn
thanks!
hope there isn't too much else in this CGP guide that I might end up learning unnecessarily..

Is an ion-dipole bond the same thing as an ion-permanent dipole bond?


Yeah it is
Original post by nukethemaly
Yeah it is


Thanks



Can anyone demonstrate what this would look like? Jan 11 2D, pasted the mark scheme on the screenshot but I don't fully know what kind of diagram they are after
jan112d.png
Original post by Kreayshawn
Thanks



Can anyone demonstrate what this would look like? Jan 11 2D, pasted the mark scheme on the screenshot but I don't fully know what kind of diagram they are after
jan112d.png


first diagram on page 96 in the cgp revision guide:smile:
Original post by calmpeach
Hey guys, hope revision is going well for you.
I've got something that I can't get my head around and it'll be great if could help me:smile:

On p55 in new edition salters revision guide by OCR it says on the top right corner (for visible absorption spectroscopy):
absorption is more intense and the wavelength of lamda-max increases for organic molecules with large delocalised systems.

correct me if I'm wrong, but I thought as the delocalisation increases, the excitation energy of electrons would decrease?
help!:frown:


You are correct, except that you have got confused between wavelength and frequency - a longer wavelength = lower frequency = less energy.
Original post by Kreayshawn
Thanks



Can anyone demonstrate what this would look like? Jan 11 2D, pasted the mark scheme on the screenshot but I don't fully know what kind of diagram they are after
jan112d.png


TSR Chem.jpg
Sorry it's a bit blurry :smile:
Original post by calmpeach
first diagram on page 96 in the cgp revision guide:smile:


Original post by Harantony
TSR Chem.jpg
Sorry it's a bit blurry :smile:


thanks guys! really appreciate you drawing it out and scanning it!
Can anyone help me? I was doing the January 2012 past paper today and stumbled upon a question about Iodine number, question 4 c (ii) and (iii). Had never come across this before, so could someone please explain it? Cheers!
Original post by matthooper95
Can anyone help me? I was doing the January 2012 past paper today and stumbled upon a question about Iodine number, question 4 c (ii) and (iii). Had never come across this before, so could someone please explain it? Cheers!


first find number of moles of elaidic acid
n = mass/Mr = 100/282 = 0.35

ratio of moles is 1:1 since 1 mole of each reactants required in reaction
so number of moles of elaidic acid = number of moles of iodine used
n x Mr = mass of iodine
0.35 x 253.8 = 90g

235.8 as iodine is I2, mass is 126.9 x 2 from periodic table

hope that all makes sense, it's just a simple molar calculation but mass of eladic acid is 100g - they just worded it strangely by calling it the "iodine number"
Original post by matthooper95
Can anyone help me? I was doing the January 2012 past paper today and stumbled upon a question about Iodine number, question 4 c (ii) and (iii). Had never come across this before, so could someone please explain it? Cheers!


This has been answered but it's not something we're explicitly taught it's just that we need to be able to use equations such a n=m/Mr, and identify when nucleophilic addition won't occur because a molecule is fully saturated :-)
I'm doing the jan 2011 paper and not sure about question 4) (f)

It says explain what is meant by a buffer solution and how a buffer solution works by referring to the equilibrium in equation 4.1.


resists pH change AW
when acid/alkali added
in small quantities
equilibrium moves to left when acid added [ORA for alkali]
removing acid / H+ [ORA for alkali] large concentration of HCO3–


The mark scheme had this answer but I dont understand the change in equlibrium- could someone explain this please!! Thank you x
Reply 179
Avatar for Tikara
Tikara
Original post by puddinboy
Can someone please explain to me how to work out how many hydrogen environments there are in a compound in NMR?

When explaining, examples would be most appreciated.

Thank you 😃


Posted from TSR Mobile


The number of main peaks with numbers on are the number of different environments.

If you count up the numbers at the tops then that's the number of hydrogens. Sorry I haven't got a diagram right now but I be on my computer in a sec


Posted from TSR Mobile

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