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Edexcel chemistry - unit 2 19th january 2012

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Original post by Cetacea
London forces (also known as instantaneous dipole-induced dipole) exist between all molecules. For example alkanes just have London forces.

Permanent dipole-permanent dipole forces exist between polar molecules only, for example HCl is polar so will have both London forces and permanent dipole-permanent dipole forces.

I read somewhere that you should be careful using the term van der Waals' forces because that can actually encompass London forces and permanent dipole-permanent dipole forces.

As for ammonia, it is a polar molecule that can form hydrogen bonds so surely it must have all three kinds of force?


Thanks.

I always use london forces anyway, i just put vdw in case anyone didn't know london

i would have thought that too- because the nitrogen is electronegative, but i'm thinking, perhaps the hydrogen bond overshadows the permanenent dipole dipole. :s-smilie:
(edited 12 years ago)
Reply 41
Original post by cisne
do pastpaper....again do it....again do it...well,im nervous too.......lets do our revision here..


yehhh :smile:
Lets do it! please ask me questions... !
Btw what resources are you using to study ?
Reply 42
Original post by aqua05
yehhh :smile:
Lets do it! please ask me questions... !
Btw what resources are you using to study ?


resources.....mine is great,actually......specially published for AS students ,for the new specification.....

ok.....lets get started...
why water is a liquid at rtp whereas hydrogen sulphide is a gas at rtp??
Reply 43
Original post by cisne
resources.....mine is great,actually......specially published for AS students ,for the new specification.....

ok.....lets get started...
why water is a liquid at rtp whereas hydrogen sulphide is a gas at rtp??


water has hydrogen bonding which is a very strong intermolecular force. hydrogen sulfide has van der waals forces and the bonds between them is very weak thus it is a gas.

My question to you
what reactants do you require for oxidation of primary & secondary alcohols? Also mention the products formed & the colour change(if any)
Reply 44
Original post by aqua05

My question to you
what reactants do you require for oxidation of primary & secondary alcohols? Also mention the products formed & the colour change(if any)


dilute H2SO4 and K2Cr2O7 at heat under reflux...colour change is orange t green..

ummm....whch products r formed btw??:rolleyes:




my question is...which of the two chlorides, NaCl or MgCl2 is more covalent???
Original post by cisne
dilute H2SO4 and K2Cr2O7 at heat under reflux...colour change is orange t green..

ummm....whch products r formed btw??:rolleyes:




my question is...which of the two chlorides, NaCl or MgCl2 is more covalent???


Mg, because it has a higher charge density than Na, so Mg will polarise/distort the chlorine atom more readily, so electron cloud is shared more, hence more covalency.
Reply 46
Original post by This Honest
Mg, because it has a higher charge density than Na, so Mg will polarise/distort the chlorine atom more readily, so electron cloud is shared more, hence more covalency.



yeh thts correct.....whrs my questn then?? also i culdnt fully ans my other questn from aqua......do u knw??
Original post by cisne
yeh thts correct.....whrs my questn then?? also i culdnt fully ans my other questn from aqua......do u knw??


:lol: I thought you actually needed to know the anser. Okay. Question:

Write out the ionic equation for soidum hydroxide reacting with bromine in hot water
Reply 48
I'm using the Edexcel AS Students Book and the CGP Revision Guide to study.

Have a go at these:

1. Write an equation for the preparation of 1-iodopropane from propan-1-ol and PI3.
2. State the colour of iodine in (a) water (b) hydrocarbon solvent.
Reply 49
Original post by This Honest
:lol: I thought you actually needed to know the anser. Okay. Question:

Write out the ionic equation for soidum hydroxide reacting with bromine in hot water


ummm i dont get the question ? is it related to syllabus !
can someone temme whats in specification ?? :smile:
Original post by Cetacea
I'm using the Edexcel AS Students Book and the CGP Revision Guide to study.

Have a go at these:

1. Write an equation for the preparation of 1-iodopropane from propan-1-ol and PI3.
2. State the colour of iodine in (a) water (b) hydrocarbon solvent.


1) CH3CH2CH2OH+ PI3 --> CH3CH2CH2I + H3P03
2) iodine in water; brown iodine in hydrocarbon solvent; purple
Original post by This Honest

Original post by This Honest
1) CH3CH2CH2OH+ PI3 --> CH3CH2CH2I + H3P03
2) iodine in water; brown iodine in hydrocarbon solvent; purple


1 is wrong. 3H3CH2CH2OH+ PI3 --> 3CH3CH2CH2I + H3P03
Original post by NutterFrutter
1 is wrong. 3H3CH2CH2OH+ PI3 --> 3CH3CH2CH2I + H3P03


i didnt balance, oh well
Original post by cisne
dilute H2SO4 and K2Cr2O7 at heat under reflux...colour change is orange t green..

ummm....whch products r formed btw??:rolleyes:




my question is...which of the two chlorides, NaCl or MgCl2 is more covalent???


mild oxidation of primary alcohol turns into propanal
vigorous oxidation of primary alcohol turns into propanoic acid

oxidation of secondary alcohol turns into ketone
it can't be further oxidised due to the stability of the alkyl groups
Reply 54
Original post by cisne
dilute H2SO4 and K2Cr2O7 at heat under reflux...colour change is orange t green..

ummm....whch products r formed btw??:rolleyes:




my question is...which of the two chlorides, NaCl or MgCl2 is more covalent???


when primary alcohol is heated with dilute H2SO4 & K2Cr2O7, the products formed are carboxylic acid via an aldehyde

When secondary alcohol is heated under reflux, ketone is formed :smile:

MgCl2 is more covalent :smile:

My question:
When doing the experiment under reflux why is it important that it remains open at the top?
(edited 12 years ago)
Reply 55
Original post by This Honest
1) CH3CH2CH2OH+ PI3 --> CH3CH2CH2I + H3P03
2) iodine in water; brown iodine in hydrocarbon solvent; purple


Hiii can you explain to me this iodine bit reacting with alcohol :frown:
I dont seem to understand it.. thanks :smile:
Reply 56
i need helppp!!!!
I was going through the experiment on alcohols reacting with sodium.. & it says when excess ethanol evaporates it forms sodium ethoxide which is a white solid.
& can anyone explain to me what happens when water is added to the white solid ???
It says ethoxide ion acts as a base & removes proton from the water, forming alkaline solution ?? :s-smilie: Can anyone give me the equation for this reaction(equation between sodium ethoxide & water..not ionic please) ??
(edited 12 years ago)
Reply 57
Is the formula for phosphorus oxychloride POCl3 ??
Reply 58
ANYONE WHO CAN SHARE SOME OF THEIR NOTES?!
Would really really appreciate that :smile:
retaking this module, got a B in it, need a bang on A to get an A overall for AS.

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