[Exam Jam on TSR] The Ultimate All-Day Chemistry Revision Thread!

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CheeseIsVeg
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Why hello there Chemistry students! :hello:

Today we hold the Chemistry All-Day Ultimate Revision Thread!





Start: 00:00 2nd June
Finish: 23:59 3rd June

Up and atom! :rave:





Pack this thread with chemistry memes, chemistry exam tips, revision questions you want answered, anything!

I am free in the morning and late evening to help out with any particular queries if nobody else is about. I just finished my first year of Chemistry at University :awesome:.

Some useful TSR links:
Find your exam discussion here.
For A level Chemistry, see here.
For GCSE level, see here.
TSR A level chemistry revision resources can be found here.
GCSE ones are here.
Here is a crammer's guide to last minute chemistry revision! :albertein:

Some useful Revision websites for chemistry:
Doc Brown (useful for any chemistry to be honest).
GCSE - Bitesize
A level - Chemguide
Khan Academy Chemistry
General Organic Chemistry - Master Organic Chemistry

Some general chemistry revision/exam tips:
-Find the revision method that works best for you
Past papers are great but if you are consistently getting some theory wrong, maybe Quizlet, writing it out, mindmaps, getting a friend to revise/learn it together in a memorable way may help you.
-Don't be afraid to ask for help
Now is the time to clear up any doubts you may have.
-Don't panic in the exam
A good way of preparing and dealing better with this is practising doing past papers in exam conditions and timing yourself well.
Be aware of time all the time.
-Be confident not just with the theory but also be aware of the applications of what you've been taught. E.g: for GCSE this can be industrial applications/instances where this compound is useful.
Hard questions in A level chemistry in particular can often come up from applying a mechanism you know for say an oxygen containing molecule but it appearing as a sulphur instead. You can use your knowledge of similar reactivity in this group to tackle this question but it's often hard to spot when you are in the heat of the moment in the exam!
-Enjoy it!
Chemistry is a great science, applicable to almost anything, in all disciplines of life. It's not easy and it can be painful at times but chemistry is kinda beautiful really :wink2:
-Good luck :grouphugs:
I know you can do it :party:
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A mole or two of memes and puns for you to enjoy:
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#noretakes
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Hi, I'm doing OCR chemistry. Does anyone have any tips on writing ligand equations. They don't really make sense to me and I can't think of a logical way of working them out. e.g Copper 2+ with excess ammonia
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CheeseIsVeg
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(Original post by #noretakes)
Hi, I'm doing OCR chemistry. Does anyone have any tips on writing ligand equations. They don't really make sense to me and I can't think of a logical way of working them out. e.g Copper 2+ with excess ammonia
Hi there! :hello:
Some general tips on writing ligand equations would be to check your spec for examples and the ones you need to know.
I actually did your spec back when I did a levels so I have a Quizlet here that might help with that.




Adding water to the green solution, replaces the chloride ions as ligands by water molecules again, and the solution returns to blue.
Image
Replacing water molecules by ammonia
Water molecules and ammonia molecules are very similar in size, and so there is no change in co-ordination this time. Unfortunately, the reactions aren't quite so straightforward to describe.
Ammonia solution can react with hexaaqua metal ions in two quite distinct ways, because it can act as a base as well as a ligand.
If you add a small amount of ammonia solution you get precipitates of the metal hydroxide - the ammonia is acting as a base. In some cases, these precipitates redissolve when you add more ammonia to give solutions in which a ligand exchange reaction has occurred.
In the diagrams below, both steps are shown, but we are only going to consider the chemistry of the overall ligand exchange reaction. The precipitates dissolve because of a complicated series of equilibrium shifts, and we shan't worry about that for the moment.


Note: You will find full details of the reactions involved in the formation of the precipitates described on a separate page about the reaction of ammonia with metal aqua ions.


That page also describes the quite complex reasons why the precipitate dissolves again.




Replacing the water in the hexaaquacopper(II) ion
This is a slightly untypical case, because only four of the six water molecules get replaced to give the tetraamminediaquacopper(II) ion, [Cu(NH3)4(H2O)2]2+.
Image
Notice that the four ammonias all lie in one plane, with the water molecules above and below.
What you see in a test tube is:
Image
The main equilibrium involved in the ligand exchange reaction is:
ImageImage
The colour of the deep blue complex is so strong that this reaction is used as a sensitive test for copper(II) ions in solution. Even if you try to reverse the change by adding large amounts of water to the equilibrium, the strength of the deep blue (even highly diluted) always masks the pale blue of the aqua ion.

Here is a really good way of explaining it courtesy of Chemguide.
Basically it is to do with how many ligands of ammonia you are reacting with the hexaaquacopper(II) ion.
Make sure you also look at the charge of your compound and once you've switched up the ligands, ensure that balances on both sides.
Then ensure all species balance too, for example: you started with 6H2O and then replaced 4 with NH3, this means that 4 moles of water is going to be left over.

Hope this helps, you can find the link to that source here
If you have any specific questions/examples you've found difficult, do not hesitate to post them and we can go through those.

Hope this helps,
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Schnedlington
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(Original post by #noretakes)
Hi, I'm doing OCR chemistry. Does anyone have any tips on writing ligand equations. They don't really make sense to me and I can't think of a logical way of working them out. e.g Copper 2+ with excess ammonia
hiya! I find these pretty hard as well 😅 so here is a quizlet i made! I find that just going through the flash cards really gets it into my head.
I hope it helps

https://quizlet.com/_4qj60e
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#noretakes
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(Original post by CheeseIsVeg)
Hi there! :hello:
Some general tips on writing ligand equations would be to check your spec for examples and the ones you need to know.
I actually did your spec back when I did a levels so I have a Quizlet here that might help with that.




Adding water to the green solution, replaces the chloride ions as ligands by water molecules again, and the solution returns to blue.


Image

Replacing water molecules by ammonia
Water molecules and ammonia molecules are very similar in size, and so there is no change in co-ordination this time. Unfortunately, the reactions aren't quite so straightforward to describe.
Ammonia solution can react with hexaaqua metal ions in two quite distinct ways, because it can act as a base as well as a ligand.
If you add a small amount of ammonia solution you get precipitates of the metal hydroxide - the ammonia is acting as a base. In some cases, these precipitates redissolve when you add more ammonia to give solutions in which a ligand exchange reaction has occurred.
In the diagrams below, both steps are shown, but we are only going to consider the chemistry of the overall ligand exchange reaction. The precipitates dissolve because of a complicated series of equilibrium shifts, and we shan't worry about that for the moment.


Note: You will find full details of the reactions involved in the formation of the precipitates described on a separate page about the reaction of ammonia with metal aqua ions.


That page also describes the quite complex reasons why the precipitate dissolves again.




Replacing the water in the hexaaquacopper(II) ion
This is a slightly untypical case, because only four of the six water molecules get replaced to give the tetraamminediaquacopper(II) ion, [Cu(NH3)4(H2O)2]2+.


Image

Notice that the four ammonias all lie in one plane, with the water molecules above and below.
What you see in a test tube is:


Image

The main equilibrium involved in the ligand exchange reaction is:
ImageImage
The colour of the deep blue complex is so strong that this reaction is used as a sensitive test for copper(II) ions in solution. Even if you try to reverse the change by adding large amounts of water to the equilibrium, the strength of the deep blue (even highly diluted) always masks the pale blue of the aqua ion.

Here is a really good way of explaining it courtesy of Chemguide.
Basically it is to do with how many ligands of ammonia you are reacting with the hexaaquacopper(II) ion.
Make sure you also look at the charge of your compound and once you've switched up the ligands, ensure that balances on both sides.
Then ensure all species balance too, for example: you started with 6H2O and then replaced 4 with NH3, this means that 4 moles of water is going to be left over.

Hope this helps, you can find the link to that source here
If you have any specific questions/examples you've found difficult, do not hesitate to post them and we can go through those.

Hope this helps,
THANK YOU SO MUCH!
Would you still regard the reaction of copper with 4 NH3 a ligand substitution reaction?
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#noretakes
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Im really stuck on Q8 of the Jan 2013 paper (linked below) part cii), if anyone could explain this I would be very grateful. The topic is transition metals.
http://www.a-levelchemistry.co.uk/up...25-01jan13.pdf
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#noretakes
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(Original post by CheeseIsVeg)
Hi there! :hello:
Some general tips on writing ligand equations would be to check your spec for examples and the ones you need to know.
I actually did your spec back when I did a levels so I have a Quizlet here that might help with that.




Adding water to the green solution, replaces the chloride ions as ligands by water molecules again, and the solution returns to blue.



Image


Replacing water molecules by ammonia
Water molecules and ammonia molecules are very similar in size, and so there is no change in co-ordination this time. Unfortunately, the reactions aren't quite so straightforward to describe.
Ammonia solution can react with hexaaqua metal ions in two quite distinct ways, because it can act as a base as well as a ligand.
If you add a small amount of ammonia solution you get precipitates of the metal hydroxide - the ammonia is acting as a base. In some cases, these precipitates redissolve when you add more ammonia to give solutions in which a ligand exchange reaction has occurred.
In the diagrams below, both steps are shown, but we are only going to consider the chemistry of the overall ligand exchange reaction. The precipitates dissolve because of a complicated series of equilibrium shifts, and we shan't worry about that for the moment.


Note: You will find full details of the reactions involved in the formation of the precipitates described on a separate page about the reaction of ammonia with metal aqua ions.


That page also describes the quite complex reasons why the precipitate dissolves again.




Replacing the water in the hexaaquacopper(II) ion
This is a slightly untypical case, because only four of the six water molecules get replaced to give the tetraamminediaquacopper(II) ion, [Cu(NH3)4(H2O)2]2+.



Image


Notice that the four ammonias all lie in one plane, with the water molecules above and below.
What you see in a test tube is:



Image


The main equilibrium involved in the ligand exchange reaction is:
ImageImage
The colour of the deep blue complex is so strong that this reaction is used as a sensitive test for copper(II) ions in solution. Even if you try to reverse the change by adding large amounts of water to the equilibrium, the strength of the deep blue (even highly diluted) always masks the pale blue of the aqua ion.

Here is a really good way of explaining it courtesy of Chemguide.
Basically it is to do with how many ligands of ammonia you are reacting with the hexaaquacopper(II) ion.
Make sure you also look at the charge of your compound and once you've switched up the ligands, ensure that balances on both sides.
Then ensure all species balance too, for example: you started with 6H2O and then replaced 4 with NH3, this means that 4 moles of water is going to be left over.

Hope this helps, you can find the link to that source here
If you have any specific questions/examples you've found difficult, do not hesitate to post them and we can go through those.

Hope this helps,
Name:  Screen Shot 2018-06-02 at 15.18.49.png
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I found this question that I'd love to have your help on please :hmmmm2:
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bantaleg
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Hey can you help with OCR A Chemistry enthalpy calculations? I don't know what to do when they ask you to find enthalpy change of formation say and the enthalpy change is given like I don't know what to do with the enthalpy change
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iamdying90
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Help with this question pls:
Q has the formula C9H8O. Compound Q can be converted into cinnamic acid which contains a carboxylic acid functional group and is a monobasic acid. 1.78g of cinnamic acid is reacted with 250cm3 of 0.500mol dm-3 NaOH. 25cm3 of the resulting solution was titrated with 0.400mol dm-3 HCl. 28.25cm3 was needed for complete neutralisation. Calculate the Mr of cinnamic acid, giving your answer to one decimal place.

Thank you xx
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#noretakes
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Hiii,

I'm not 10000% sure what you mean but my rule of thumb for enthalpy change of formation is, if you are given the enthalpy changes for different elements its the (sum of the products)- (the sum of the reactants) remembering to check the stoichiometry.


(Original post by bantaleg)
Hey can you help with OCR A Chemistry enthalpy calculations? I don't know what to do when they ask you to find enthalpy change of formation say and the enthalpy change is given like I don't know what to do with the enthalpy change
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ireee
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(Original post by #noretakes)
Name:  Screen Shot 2018-06-02 at 15.18.49.png
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I found this question that I'd love to have your help on please :hmmmm2:
https://www.chemguide.co.uk/inorgani...igandexch.html
This should help explain
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