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OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

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Original post by BioStudentx
Less twitch and more revision could have fixed that :wink:


Firstly equilibrium not equation (I'm just being picky as an examiner would - it's nice to get in a good habit). The Mg2+ would react with the acid, so position of Eqbm would shift to the right to restore lost H+ ions. Remember, Mg2+ is a base!


Oh so that is one of those insoluble bases, is any Metal ion a base?
Original post by Dinasaurus
Guys if you add Magnesium to a buffer solution, which way does the equation shift?

C2h5COOH = H+ + C2H5COO-

Then you add Mg2+

I'm guessing Mg2+ reduces the amount of salt and makes more acid?

Wait no, Mg2+ makes acid dissaciate so makes more salt?


i thought that metal reacts with an acid to form hydrogen given off as a gas and a salt

so it'd be (c2h5coo)2mg
Original post by Dinasaurus
Guys if you add Magnesium to a buffer solution, which way does the equation shift?

C2h5COOH = H+ + C2H5COO-

Then you add Mg2+

I'm guessing Mg2+ reduces the amount of salt and makes more acid?

Wait no, Mg2+ makes acid dissaciate so makes more salt?


Basically, the Mg (and any strong alkali) reacts with the HA to produce the salt. This means that you're effectively taking away the mol of Mg from the mol of HA and adding it to the mol of A-.
The position of the equilibrium shifts to counter the deficit in HA, therefore, reducing the change in pH.
(edited 7 years ago)
Original post by Dinasaurus
Oh so that is one of those insoluble bases, is any Metal ion a base?

All metal ions are bases. Saying Mg2+ is basically the same thing as saying Mg(OH)2
Original post by ReTakingF324/5
Forsen Boys. This exam is gonna be so easy Kappa. I'm ****ed boys!


Can I get some PogChamps in the tsr chat for another U grade student 4Head.
Original post by ShannonD_1697
Could someone quickly explain how ionic size and charge effects lattice enthalpy?


Erm strong charge means more attractive force, means stronger ionic bond means more exothermic.
If two ions have the same charge then latice enthalpy is more exothermic as radius decreases because it means charge density is higher, as the forces of attraction has to travel less far so it is stronger.
Original post by BioStudentx
All metal ions are bases. Saying Mg2+ is basically the same thing as saying Mg(OH)2


Keep it coming i'm learning from this :wink:
Reply 3147
Original post by BioStudentx
All metal ions are bases. Saying Mg2+ is basically the same thing as saying Mg(OH)2


wtf are you on about
Original post by BanterBus
Can I get some PogChamps in the tsr chat for another U grade student 4Head.

-( ͡° ͜ʖ ͡°)╯╲___U

Don't mind me just taking my U for a walk
Can anyone give a rough overview about what happens at each electrode in a fuel cell? Pleasee :tongue:
Original post by alow
wtf are you on about

I was making the (crude) assumption that he's talking about reacting Mg(OH)2 with an acid. As during buffer/neutralisation questions they'd state to add Mg(OH)2, not just leave it as "Mg2+".
lol i find last year's paper hard
Original post by ShannonD_1697
Could someone quickly explain how ionic size and charge effects lattice enthalpy?


There's a really good description of it from here:
http://www.chemguide.co.uk/physical/energetics/lattice.html
Original post by sydneyl3igh
Can anyone give a rough overview about what happens at each electrode in a fuel cell? Pleasee :tongue:


You have both alkali and acidic half equations (I'm fairly sure you need to memorise both, it can be derived but takes time). I posted them a few pages ago.
Reply 3154
Original post by BioStudentx
I was making the (crude) assumption that he's talking about reacting Mg(OH)2 with an acid. As during buffer/neutralisation questions they'd state to add Mg(OH)2, not just leave it as "Mg2+".


Please never call a metal ion a base. That is incorrect in every way.
Original post by alow
Please never call a metal ion a base. That is incorrect in every way.

So in answer to his question, adding "Mg2+ (whatever that means)" will shift the position of eqbm in which direction? Or is that not even a thing? I think he meant Mg(OH)2?
Original post by BioStudentx
So in answer to his question, adding "Mg2+ (whatever that means)" will shift the position of eqbm in which direction? Or is that not even a thing? I think he meant Mg(OH)2?


Shift to the left, there's less [HA] and more [A-]
Original post by tomlam
Shift to the left, there's less [HA] and more [A-]


So is Mg2+ an acid or a base? >.< Holy **** i'm screwed (and confused).
Can someone explain the Buffer solution question for june 15? The mg part?

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Reply 3159
Original post by BioStudentx
So is Mg2+ an acid or a base? >.< Holy **** i'm screwed (and confused).


Transition metal ions can be considered Lewis acids, like halogen carriers such as FeBr3.

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