Edexcel chemistry - unit 2 19th january 2012
Chemistry exam discussion - share revision tips in preparation for GCSE, A Level and other chemistry exams and discuss how they went afterwards.
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Re: Edexcel chemistry - unit 2 19th january 2012Thanks.(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?
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.
Last edited by Dalimyr; 13-01-2012 at 21:48. -
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Re: Edexcel chemistry - unit 2 19th january 2012yehhh(Original post by cisne)
do pastpaper....again do it....again do it...well,im nervous too.......lets do our revision here..
Lets do it! please ask me questions... !
Btw what resources are you using to study ? -
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Re: Edexcel chemistry - unit 2 19th january 2012resources.....mine is great,actually......specially published for AS students ,for the new specification.....(Original post by aqua05)
yehhh
Lets do it! please ask me questions... !
Btw what resources are you using to study ?
ok.....lets get started...
why water is a liquid at rtp whereas hydrogen sulphide is a gas at rtp?? -
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Re: Edexcel chemistry - unit 2 19th january 2012water 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.(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??
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) -
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Re: Edexcel chemistry - unit 2 19th january 2012dilute H2SO4 and K2Cr2O7 at heat under reflux...colour change is orange t green..(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)
ummm....whch products r formed btw??
my question is...which of the two chlorides, NaCl or MgCl2 is more covalent??? -
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Re: Edexcel chemistry - unit 2 19th january 2012Mg, 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.(Original post by cisne)
dilute H2SO4 and K2Cr2O7 at heat under reflux...colour change is orange t green..
ummm....whch products r formed btw??
my question is...which of the two chlorides, NaCl or MgCl2 is more covalent??? -
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Re: Edexcel chemistry - unit 2 19th january 2012(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?? -
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Re: Edexcel chemistry - unit 2 19th january 2012(Original post by cisne)
yeh thts correct.....whrs my questn then?? also i culdnt fully ans my other questn from aqua......do u knw??
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 -
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Re: Edexcel chemistry - unit 2 19th january 2012I'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. -
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Re: Edexcel chemistry - unit 2 19th january 2012ummm i dont get the question ? is it related to syllabus !(Original post by This Honest)
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
can someone temme whats in specification ??
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Re: Edexcel chemistry - unit 2 19th january 20121) CH3CH2CH2OH+ PI3 --> CH3CH2CH2I + H3P03(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.
2) iodine in water; brown iodine in hydrocarbon solvent; purple -
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Re: Edexcel chemistry - unit 2 19th january 20121 is wrong. 3H3CH2CH2OH+ PI3 --> 3CH3CH2CH2I + H3P03(Original post by This Honest)
1) CH3CH2CH2OH+ PI3 --> CH3CH2CH2I + H3P03
2) iodine in water; brown iodine in hydrocarbon solvent; purple -
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Re: Edexcel chemistry - unit 2 19th january 2012i didnt balance, oh well(Original post by NutterFrutter)
1 is wrong. 3H3CH2CH2OH+ PI3 --> 3CH3CH2CH2I + H3P03 -
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Re: Edexcel chemistry - unit 2 19th january 2012mild oxidation of primary alcohol turns into propanal(Original post by cisne)
dilute H2SO4 and K2Cr2O7 at heat under reflux...colour change is orange t green..
ummm....whch products r formed btw??
my question is...which of the two chlorides, NaCl or MgCl2 is more covalent???
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 -
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Re: Edexcel chemistry - unit 2 19th january 2012when primary alcohol is heated with dilute H2SO4 & K2Cr2O7, the products formed are carboxylic acid via an aldehyde(Original post by cisne)
dilute H2SO4 and K2Cr2O7 at heat under reflux...colour change is orange t green..
ummm....whch products r formed btw??
my question is...which of the two chlorides, NaCl or MgCl2 is more covalent???
When secondary alcohol is heated under reflux, ketone is formed
MgCl2 is more covalent
My question:
When doing the experiment under reflux why is it important that it remains open at the top?Last edited by aqua05; 14-01-2012 at 05:48. -
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Re: Edexcel chemistry - unit 2 19th january 2012Hiii can you explain to me this iodine bit reacting with alcohol(Original post by This Honest)
1) CH3CH2CH2OH+ PI3 --> CH3CH2CH2I + H3P03
2) iodine in water; brown iodine in hydrocarbon solvent; purple
I dont seem to understand it.. thanks
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Re: Edexcel chemistry - unit 2 19th january 2012i 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 ?? Can anyone give me the equation for this reaction(equation between sodium ethoxide & water..not ionic please) ??
Last edited by aqua05; 14-01-2012 at 07:53.
