OCR B Salters - F335 Exam - 15 June 2011

Scroll to see replies

Reply 420

Adam9

Original post by thatgu

Acidified potassium dichromate orange/yellow to green/blue.

ALWAYS say orange to green - mark schemes can be specific

Reply 421

thatgu

Original post by Adam9

ALWAYS say orange to green - mark schemes can be specific

I agree but what I said was copied from the june 2010 mark scheme

Reply 422

Adam9

Original post by thatgu

I agree but what I said was copied from the june 2010 mark scheme

Oh right, sorry about that, but i'll play it safe with orange to green, just incase this mark scheme is different - And I have noticed changes in the MS from year to year - Probably get marks for both

Reply 423

chris3321

Thanks, didn't think there would be many but wanted to make sure

Reply 424

Jhyzone

Original post by JAshcroft

Has anyone attempted the last two parts of the Jan 11 paper? 5 (f) (ii) and (iii)?

From the mark scheme it says:
i) titration with alkali / base / named strong alkali ? standard / known concentration
ii) 0.7

(edited 12 years ago)

Reply 425

Jamesrb

Original post by Jhyzone

From the mark scheme it says:
i) titration with alkali / base / named strong alkali ? standard / known concentration
ii) 0.7

I don't understand where the 0.7 comes from :s-smilie:

Does anybody fancy summarising what they believe will come up?

Reply 426

Jhyzone

Original post by chris3321

Thanks, didn't think there would be many but wanted to make sure

Nitrogen compunds colours:

Brown NO2 (Nitrogen dioxide)
colourless N2O (dinitrogen gas)
colourless NO (nitrogen monoxide)
colourless N2 (Nitrogen gas)

Reply 427

Ollie901

Original post by Jamesrb

Does anybody fancy summarising what they believe will come up?

I'm expecting a big GLC question. I dont think its come up yet in the new spec.

Reply 428

RayM

What side groups modify the chromophore causing a change in colour?
Is it side groups with lone pairs or side groups with double bonds?

Reply 429

Ollie901

Original post by RayM

What side groups modify the chromophore causing a change in colour?
Is it side groups with lone pairs or side groups with double bonds?

My revision guide says NH2 or NR2, so I guess its the ones with the lone pairs.

Reply 430

Adam9

Original post by Jamesrb

I don't understand where the 0.7 comes from :s-smilie:

Does anybody fancy summarising what they believe will come up?

there is 1.1 mol of reactants, and then there is only 0.4 mol at the end, so there must be (1.1 mol - 0.4 mol) of product which is 0.7 mol ......... therefore, 0.7 mol of ester

Reply 431

Adam9

Original post by Ollie901

My revision guide says NH2 or NR2, so I guess its the ones with the lone pairs.

I know that lone pairs definitely extend the delocalisation of the chromophore, and therefore change the colour ... double bonds like C=C and N=N do affect delocalisation when in the middle of arenes, but i am not sure if they do as side chains

Reply 432

Ollie901

Original post by Adam9

They do I think. The last question on the CD end of module test is
"why is the substitution of an acyl group, such as -COCH3, in dye B likely to change its colour?" (Swapping a H for it on the ring) and the answer is because it extends the chromaphore.

Reply 433

*Rainbow*

Does anyone get curly arrows?

Reply 434

AGM

Original post by *Rainbow*

Does anyone get curly arrows?

I get them as in it's the movement of electrons in the reaction mechanism(full headed arrow = 2 electrons half headed arrow = 1 electron)

However, I nearly always get them wrong!

Reply 435

gozatron

If it asks us to circle the chromophor do you only circle the delocised areas, Eg) double bonds, aril groups or them and functional groups such as -NH2?

Reply 436

*Rainbow*

Original post by AGM

I get them as in it's the movement of electrons in the reaction mechanism(full headed arrow = 2 electrons half headed arrow = 1 electron)

However, I nearly always get them wrong!

Yeah that's what i mean.. How on earth are we supposed to know all the different scenarios.. is it a case of learning or is there an actual method to it?

Reply 437

TheTomD

Original post by *Rainbow*

Does anyone get curly arrows?

They just show the movement of electrons, [mainly] used in the addition/substitution reaction diagrams. Just draw a curly arrow to denote the movement of electrons-

For example, in the nucleophilic addition reaction of CN to an aldehyde, the 'negative' CN molecule is attracted to the slightly positive carbon (bonded to O, =O ).
The negativity of the triple bonded CN causes a pair of electrons to move from the = bond at C=O to the O, so a curly arrow is drawn FROM the bond to the O.
A curly arrow is drawn from the C of CN to show the movement of two electrons (lone pair, I think) to the +ve C.

That's hard to explain, but just know the reaction mechanisms and it'll go hand-in-hand with that. Not too much to worry about... :rolleyes:

Reply 438

TheTomD

Original post by gozatron

If it asks us to circle the chromophor do you only circle the delocised areas, Eg) double bonds, aril groups or them and functional groups such as -NH2?

I think it's just the delocalised system.

Also, a note- it's delocalised, not delocised. And 'aryl', not aril.
I hope you don't put either in the exam! :wink:

Reply 439

gozatron

Original post by TheTomD

I think it's just the delocalised system.

Also, a note- it's delocalised, not delocised. And 'aryl', not aril.
I hope you don't put either in the exam! :wink: