Edexcel AS Chemistry Unit 2 Thread

jonathan3909

But cyclohexene is polar-Its written in the edexcel book :confused:

If that's true, I'm guessing cyclohexanol is more polar due to O-H group while hexene does not have...

Reply 161

SK-mar

1

jonathan3909

But cyclohexene is polar-Its written in the edexcel book :confused:

in terms of IR spectra then it is very very very slightly polar as its bonds can abosorb radiation. But in the terms of your original question its very slight polarity is irrelevant.

Reply 162

killfestab

can anyone else do QUESTION 4 on the iodine/thiosulfate titration in the EDEXCEL AS CHEMISTRY page 253, and tell me what answer they get ? :smile:

For part (iii) I got 0.025 and for (iv) I got 1.775

Reply 163

SK-mar

in terms of IR spectra then it is very very very slightly polar as its bonds can abosorb radiation. But in the terms of your original question its very slight polarity is irrelevant.

Open page 158 of the book and it says cyclohexene is deflected :confused:

Reply 164

killfestab

5

jonathan3909

For part (iii) I got 0.025 and for (iv) I got 1.775

i got the same,
cheers :smile:

btw, three significant figures...

Reply 165

Phalange

If that's true, I'm guessing cyclohexanol is more polar due to O-H group while hexene does not have...

The book says in cyclohexene ,ther is a planar C = C part of the molecule so it is polar :confused:

Reply 166

SK-mar

1

OK theres one thing thats majorrrrrly annoying me! ..... can someone put a step by process of the formation of a BROMO/IODO halogenoalkane from an alcohol please. I know you use phosphoric acid but howwwww? thank you in advance

is it for example:

KBr + H3PO4 = HBr + KH2PO4

C2H5OH + HBr = C2H5Br + H2O

???

Reply 167

http://www.chemguide.co.uk/organicprops/haloalkanes/making.html

killfestab

i got the same,
cheers :smile:

btw, three significant figures...

Last page,Q 7 (b) and (c) :confused:

one sec lemme do it

*SOLVE it :P

SK-mar

OK theres one thing thats majorrrrrly annoying me! ..... can someone put a step by process of the formation of a BROMO/IODO halogenoalkane from an alcohol please. I know you use phosphoric acid but howwwww? thank you in advance

is it for example:

KBr + H3PO4 = HBr + KH2PO4

C2H5OH + HBr = C2H5Br + H2O

???

Reply 171

killfestab

5

7b)
i) The second spectra is for compound C because it is the only compound with an -OH functional group and thus we see a peak around 3200 cm^-1

ii) The other spectrum has a shark peak at around 1750 cm^-1 and that is indicative of the C=O functional group i.e. an aldehyde or ketone

c)
i) Compound C will react with bromine dissolved in hexane, and we will see a colour change from orange/red to colourless

ii) C6H5CHBrHBrCH2OH

Reply 172

killfestab

*SOLVE it :P

Last spectrum is of C as (O-H) hydrogen bonding peak is there and it also does not have major C=O peak.

C will react in bromine/hexane solution and brown color will disappear??

Reply 173

SK-mar

OK theres one thing thats majorrrrrly annoying me! ..... can someone put a step by process of the formation of a BROMO/IODO halogenoalkane from an alcohol please. I know you use phosphoric acid but howwwww? thank you in advance

is it for example:

KBr + H3PO4 = HBr + KH2PO4

C2H5OH + HBr = C2H5Br + H2O

???

Works with any halogenoalkane to be honest, but the reason why you do this with bromo/iodo is because HBr and HI are not easy to get hold of so you need to make it

I always wrote it but...
(1) Add damp red phosphorous to Br2 (or I2) to produce a hydrogen halide
H3PO4(l) + 3KBr(s) --> K3PO4 + 3HBr(g)

(2) React the hydrogen halide with the alcohol
CH3OH + HBr --> CH3Br + H2O

Reply 174

jonathan3909

The book says in cyclohexene ,ther is a planar C = C part of the molecule so it is polar :confused:

Ok this is what I think. It is polar but it is such a small degree it doesn't matter (cyclohexene). OH is much more significant factor. Don't worry too much we don't have to know a lot on cycloalkanes...

Cyclohexanol definately is not symmetrical so it has polar OH bond that will be affected by water

Edit: LOL I've been thinking about this too and now I'm ******** myself I can't find the right answer

EDIT2: WAit... is that a past paper question or a question in a book? If it was in a book, there can be more than one answer (I would pick cyclohexanol + cyclohexene) BUT if it was in exam I'd pick cyclohexanol as it is a strong more obvious answer

Reply 175

killfestab

5

Phalange

I always wrote it but...
(1) Add damp red phosphorous to Br2 (or I2) to produce a hydrogen halide
H3PO4(l) + 3KBr(s) --> K3PO4 + 3HBr(g)

Doesn't Refluxing with red Phosphorus follow this equation:

2P(s) + 3Br2 (l) --> 2PBr3 (l)

Reply 176

SK-mar

1

Phalange

Works with any halogenoalkane to be honest, but the reason why you do this with bromo/iodo is because HBr and HI are not easy to get hold of so you need to make it

I always wrote it but...
(1) Add damp red phosphorous to Br2 (or I2) to produce a hydrogen halide
H3PO4(l) + 3KBr(s) --> K3PO4 + 3HBr(g)

(2) React the hydrogen halide with the alcohol
CH3OH + HBr --> CH3Br + H2O

thankssss, does my equation work too or is yours better to use. ALsooo, is it ok just to put 'red' phosphorous instead of concentrated phosphoric acid? cheers :smile:

Reply 177

dunnoaboutme

can someone please help me with one thing, basically a test for group 7 halides is when you add AgNO3, but then you can add NH3, then you can add an organic solvent such as hexane to confirm the test am i right?

so when you add hexane to bromine i know you get a red solution, but what do you get with iodine and chlorine??

Reply 178

SK-mar

thankssss, does my equation work too or is yours better to use. ALsooo, is it ok just to put 'red' phosphorous instead of concentrated phosphoric acid? cheers :smile:

Oops wrong equation BUT you can use any...
Red yes you have to say red. Here wait...

BROMO/IODO ALKANES:
1) Add damp red phosprous to the halogen (e.g. Br2), then add alcohol
2P + 3Br2 ----> 2PBr3
CH3OH + PBr3 ---> CH3Br + H3PO3

2) Add phosphoric (V) acid to metal halide then add alcohol
3NaBr + H3PO4 ---> Na3PO4 + 3HBr
CH3OH + HBr ----> CH3Br + H2O

These are the best ways. My Edexcel book says use 50% concentrated sulphuric acid but the problem is that sulphuric acid would oxidise the HBr to produce Br2 (a by-product, reducing yield) it even oxidses HI even more... so I would not use sulphuric acid at all but sometimes in questions they use 50%..
Here:
1) Add 50% H2SO4 + NaBr, then add an alcohol
NaBr + H2SO4 ---> NaHSO4 + HBr
CH3OH + HBr ----> CH3Br + H2O

killfestab

Doesn't Refluxing with red Phosphorus follow this equation:

2P(s) + 3Br2 (l) --> 2PBr3 (l)

Yes sorry I put down phosphoric acid method by accident

Reply 179