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Edexcel - Chemistry Unit 2 - 4 June 2013

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Reply 720
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Gnome :)
2
Original post by James A
That's odd, I got a data booklet for my AS Chem exams, this was back in June 2011 so I dunno if it's changed since.


Strange. In the Data Book itself it says it is to be used in units 4, 5 and 6...
How is it that this molecule does not form hydrogen bonds?What bonds does it form and why?

Original post by awesomesoccerfan
How is it that this molecule does not form hydrogen bonds?What bonds does it form and why?



It doesnt form Hydrogen bonds because there is no Hydrogen attached to an oxygen,nitrogen or flourine. It does have London forces between the carbons and hydrogens and it forms a permanent dipole between the oxygen and the carbons because of the difference in electronegativity
Reply 723
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Lili94
Original post by awesomesoccerfan
How is it that this molecule does not form hydrogen bonds?What bonds does it form and why?




For hydrogen bonding to occur, hydrogen must be bonded to a highly electronegative element such as fluorine, oxygen or nitrogen. In the molecule above, hydrogen is only bonded to carbon which is not very electronegative.

However, it can form London forces (all molecules do) and also permanent dipole-dipole interactions due to the oxygen bonded to carbon.
Original post by Maybenexttime
Do you need to know the specifics of the uses of halogenoalkanes? i.e. do you need to know the actual names like PTFE, polychloroethane, HCFC's etc?


Could someone reply please? :biggrin:
Reply 725
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Goods
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Original post by Maybenexttime
Could someone reply please? :biggrin:


They can he used as fire retardants and aerosols


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Reply 727
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Mimi85
I have phy the next day and im done :-):-):-):-):-):-)
Reply 728
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Londrinna
Original post by Maybenexttime
Could someone reply please? :biggrin:


Think all you need to know is there general uses, don't think we have to know the names of them..


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Reply 729
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Jayqwe
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Are the halogens good oxidising or reducing agents? I guess it is reducing, but why does the reducing power increase down the group?
Reply 730
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Mimi85
can someone please explain chemical eq for concentration ??
It has almost definately been asked before, but -
Can someone give me a model answer as to why carbonates and nitrates become more stable to heat as the group is descended?
Original post by Jayqwe
Are the halogens good oxidising or reducing agents? I guess it is reducing, but why does the reducing power increase down the group?


They are oxidising agents, and strength decreases down the group.

The reducing power increases down the group because, they are reducing agents, if they themselves are oxidised. Oxidation is Loss of electrons. So, the halogens that lose electrons more easily, are better reducing agents. And Iodide loses electrons more easily than bromide because of the larger radius and increased sheilding.

Hope this helps.

EDIT: @posthumus thanks for the correction on the 'ide' as we are talking about ions, not molecules.
(edited 10 years ago)
Reply 733
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posthumus
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Original post by Jayqwe
Are the halogens good oxidising or reducing agents? I guess it is reducing, but why does the reducing power increase down the group?


Chlorine is best oxidizing agent & iodide (not iodine) is the best reducing agents. I'm guessing because chlorine is far more electronegative it attracts the electron to a greater extent. Whereas iodine with it's big radius is more likely to be oxidized itself.


Original post by Mimi85
can someone please explain chemical eq for concentration ??


Increasing the concentration on one side, will always shift equilibrium in the opposite direction I believe. Ignore any solids.
Reply 734
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Jayqwe
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Original post by beaver_tron
They are oxidising agents, and strength decreases down the group.

The reducing power increases down the group because, they are reducing agents, if they themselves are oxidised. Oxidation is Loss of electrons. So, the halogens that lose electrons more easily, are better reducing agents. And Iodine loses electrons more easily than bromine because of the larger radius and increased sheilding.

Hope this helps.

Original post by posthumus
Chlorine is best oxidizing agent & iodide (not iodine) is the best reducing agents. I'm guessing because chlorine is far more electronegative it attracts the electron to a greater extent. Whereas iodine with it's big radius is more likely to be oxidized itself.


Thank you guys, it all makes sense now
Reply 735
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Jayqwe
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Original post by posthumus
Chlorine is best oxidizing agent


What about Fluorine?
Original post by Jayqwe
What about Fluorine?


Fluoride isn't mentioned in the revision guide, however, it does say you should be able to make assumptions about Flourine and Astatine in the spec.

So, Fluoride would be the strongest oxidising agent, as the strength decreases down the group.

It would therefore be the weakest reducing agent, as strength increases down the group.

Like i say though, it is not mentioned in the book, so I would just make sure you can predict its properties, and be done with it. Also remember you need to be able to predict electronegativity and standard states etc.

EDIT: It also does not look like Fluoride is mentioned in the George Facer book either, in terms of oxidisation.
the revision guide simply says, in the predictions of Fluorine "Fluorine will be the most oxidizing"
(edited 10 years ago)
Reply 737
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Jayqwe
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Original post by beaver_tron
Fluoride isn't mentioned in the revision guide, however, it does say you should be able to make assumptions about Flourine and Astatine in the spec.

So, Fluoride would be the strongest oxidising agent, as the strength decreases down the group.

It would therefore be the weakest reducing agent, as strength increases down the group.

Like i say though, it is not mentioned in the book, so I would just make sure you can predict its properties, and be done with it. Also remember you need to be able to predict electronegativity and standard states etc.

Ok thanks
Because as you go down group 2 the size of the cation increases so as u go down group 2 the polarity if the group 2 cation decreses this means that im the ionic hond between a group 2 metal and a carbonate or nitrate as yoy go down group 2 tje anion is less polarised! This in turn means that the bond is more ionic and less covalent thus making it more thermally stable! (Because the more ionic the more thermally stable or the more distorted the ionic hond tue less thermally stable)
Original post by Sciencefella
Because as you go down group 2 the size of the cation increases so as u go down group 2 the polarity if the group 2 cation decreses this means that im the ionic hond between a group 2 metal and a carbonate or nitrate as yoy go down group 2 tje anion is less polarised! This in turn means that the bond is more ionic and less covalent thus making it more thermally stable! (Because the more ionic the more thermally stable or the more distorted the ionic hond tue less thermally stable)


Think you meant to quote me, so, the cation gets larger, so less distortion/polarisation of the anion, so more ionic, so stronger bond, so more heat to break ?

Thanks.

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