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Ocr f321 23 may 2013~official discussion thread

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Original post by MathsNerd1
Yeah that sounds a lot better :smile: Ask me a question now?


What are Displacement Reactions?
Equations for Bleach.
Colours of displacement
(edited 10 years ago)
Original post by ADAOBI123
Hmmmmmmm

Describe how van der waals forces arise ? :wink:


Van der waals arise because in a molecule there is an electron cloud, which at any given moment could be unevenly distributed which would cause a dipole, this would then induce a dipole on a neighbouring molecule which are held together by these weak intermolecular forces called van der waals forces, these don't require much energy to break and this explains the reason why the melting point of a simple molecular compound is very low. :smile:
Original post by MathsNerd1
Of course! Sorry I was having a bit of a moment, so the nuclear charge that does increase won't effect the overall result too much?


That's right :smile: As it is outweighed by the effect of an increase in atomic radius and electron shielding which weaken the electrostatic attraction between the nucleus and the outer shell electrons (more than an increase in nuclear charge would strengthen it)
Original post by MathsNerd1
Van der waals arise because in a molecule there is an electron cloud, which at any given moment could be unevenly distributed which would cause a dipole, this would then induce a dipole on a neighbouring molecule which are held together by these weak intermolecular forces called van der waals forces, these don't require much energy to break and this explains the reason why the melting point of a simple molecular compound is very low. :smile:


Good, however the bolded part that was not needed, I follow the mark scheme word by word :biggrin:
Original post by yodawg321
What is Displacement Reactions.
Equations for Bleach.
Colours of displacement


Okay, this could be my weak area and how I see it is that a displacement reaction is where a more reactive halide is able to swap positions with another one, therefore displacing it.

The equation is Cl2 + 2NaOH -----> NaClO + NaCl + H20

The colours of displacement are orange and violet. Orange when chlorine displaces bromide.
Violet when chlorine displaces iodide and Bromine displaces iodide ?
Original post by ADAOBI123
Hmmmmmmm

Describe how van der waals forces arise ? :wink:


Uneven distribution of electrons in molecule
Creates instantaneous dipole
Induces other dipoles
V.D.W forces are created
Original post by niniesta96
That's right :smile: As it is outweighed by the effect of an increase in atomic radius and electron shielding which weaken the electrostatic attraction between the nucleus and the outer shell electrons (more than an increase in nuclear charge would strengthen it)


Okay thanks, I'll try to remember this for Thursday :biggrin: What type of questions do you feel will appear?
Original post by yodawg321
Uneven distribution of electrons in molecule
Creates instantaneous dipole
Induces other dipoles
V.D.W forces are created


Spot on ! :biggrin::biggrin:
Original post by yodawg321
What is Displacement Reactions.
Equations for Bleach.
Colours of displacement


1. Displacement reactions refer to those which can be used to determine the more reactive halogen. It involves the more reactive halogen in its atomic state diplacing the less reactive halogen in its ionic state to become ionic itself e.g.
Cl2 + 2Br- -> Br2 + 2Cl-

2. Cl2 (g) + 2NaOH (aq) -> NaCl (aq) + NaClO (aq) + H2O (l)

3. In both water and cyclohexane chlorine = pale-green, bromine= prange in both and iodine= brown in water and deep purple in cylcohexane (as it is more soluble in the latter)
:smile:
Original post by ADAOBI123
Good, however the bolded part that was not needed, I follow the mark scheme word by word :biggrin:


I know but I feel like I want to test myself even further in each question that I practice on :smile:
Original post by MathsNerd1
Okay, this could be my weak area and how I see it is that a displacement reaction is where a more reactive halide is able to swap positions with another one, therefore displacing it.

The equation is Cl2 + 2NaOH -----> NaClO + NaCl + H20

The colours of displacement are orange and violet. Orange when chlorine displaces bromide.
Violet when chlorine displaces iodide and Bromine displaces iodide ?


Br and I will be orange I think?

For bleach you can also do CL2 + H2O ---> HClO + HCl

Not going to worry about this that much because this came up in Jan, don't think they will ask us this again
Original post by MathsNerd1
I know but I feel like I want to test myself even further in each question that I practice on :smile:


Okay, your turn, ask me a question.
Original post by MathsNerd1
Okay thanks, I'll try to remember this for Thursday :biggrin: What type of questions do you feel will appear?


I think there will be some on Ionisation Energy- they are yet to ask us to explain why the trend across the period fluctuates (basically because of sub-shells) which would be a tricky question.
Original post by yodawg321
Br and I will be orange I think?

For bleach you can also do CL2 + H2O ---> HClO + HCl

Not going to worry about this that much because this came up in Jan, don't think they will ask us this again


Well I always think that bromine has to be involved to be orange as that's the colour of bromine water. And oh snap, what reaction did I do then? :-/
Original post by ADAOBI123
Okay, your turn, ask me a question.


Okay. Explain what a disproportionation reaction is and give an example of one.
Original post by niniesta96
I think there will be some on Ionisation Energy- they are yet to ask us to explain why the trend across the period fluctuates (basically because of sub-shells) which would be a tricky question.


Well I don't think they've asked the defintion of successive ionisation energy, that could throw some people off and that wouldn't really bother me too much as it'll increase because of the nuclear charge increasing, the atomic radius decreasing and similiar effects from electron shielding as they're within the same outer shell.

Would that be okay for an answer? Obviously going into a bit more detail about it .
Hey guys.
(Not sure if this is off-topic of everyone asking questions at the moment, but ah ...)

Do you think any questions relating to the atomic model etc will come up ? It's a small part and I myself think its not going to. But being me, I have the urge to go through EVERY page of my book. :P

Thanks.
Original post by MathsNerd1
Okay. Explain what a disproportionation reaction is and give an example of one.


A disproportionation reaction is where an element is being oxidised and reduced.

Cl2+2NaOH -----> NaCl + NaClO+H2O
Original post by ADAOBI123
A disproportionation reaction is where an element is being oxidised and reduced.

Cl2+2NaOH -----> NaCl + NaClO+H2O


Correct! My turn :smile:
Original post by Loquacious
Hey guys.
(Not sure if this is off-topic of everyone asking questions at the moment, but ah ...)

Do you think any questions relating to the atomic model etc will come up ? It's a small part and I myself think its not going to. But being me, I have the urge to go through EVERY page of my book. :P

Thanks.


To be quite honest I've never even bothered to learn any of the green coloured pages, also on the periodic table part as I highly doubt that it'll ever show up. :tongue:

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