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

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Please never call a metal ion a base. That is incorrect in every way.

I agree. HA would react with the Mg2+ ions but a proton itself would be repelled by the positive charges. Its the OH- in Mg(OH-)2 that makes it a base. So yes it would react with the HA Itself but not the protons.

CH3COOH <---------> CH3COO- + H+

Mg2+ would form Mg2+(CH3COO-)2 + 2H+

So for the buffer, the equilibrium would move ultimately left as more CH3COO- ions and H+ ions would be produced from reaction with Mg2+.

(edited 7 years ago)

Reply 3161

BioStudentx

Original post by alow

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

Rightt? But it doesn't actually have a proton to donate?

[HA]<---> [H+] + [A-]

So it reacts with A- and equilibrium shifts to the left?

Reply 3162

BanterBus

Original post by BioStudentx

So is Mg2+ an acid or a base? >.< Holy **** i'm screwed (and confused).

+1 dw, wish i never read this thread now... it cant give any H+ ions how can it be an acid LOL

Reply 3163

alow

Original post by BioStudentx

Rightt? But it doesn't actually have a proton to donate?

[HA]<---> [H+] + [A-]

So it reacts with A- and equilibrium shifts to the left?

I said a Lewis acid, not a Brønsted–Lowry acid.

Reply 3164

alow

Original post by BanterBus

+1 dw, wish i never read this thread now... it cant give any H+ ions how can it be an acid LOL

A Lewis acid.

Reply 3165

tomlam

Original post by BioStudentx

So is Mg2+ an acid or a base? >.< Holy **** i'm screwed (and confused).

It's acting as a conjugate acid

Reply 3166

BanterBus

Original post by alow

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

alow m8 just allow it, for this spec we dont need to know Lewis acids, take it to another thread.

Reply 3167

alow

Original post by BanterBus

alow m8 just allow it, for this spec we dont need to know Lewis acids, take it to another thread.

Clearly you do, because if not you won't be able to understand these equilibria.

Reply 3168

tomlam

Original post by alow

A Lewis acid.

haven't kept up with the discussion in recent minutes but where's the lone pair that it's accepting to become a lewis acid?

Reply 3169

lai812matthew

Original post by BioStudentx

Rightt? But it doesn't actually have a proton to donate?

[HA]<---> [H+] + [A-]

So it reacts with A- and equilibrium shifts to the left?

it accepts an electron pair so it is a lewis acid. i'm not sure if they ask for lewis acids and bases in exam????? it is in the book's blue boxes.

Reply 3170

Lazerjazer

anyone got the mark scheme for the June 15 paper?

Reply 3171

alow

Original post by tomlam

haven't kept up with the discussion in recent minutes but where's the lone pair that it's accepting to become a lewis acid?

It can form an adduct with two acetate ions.

Reply 3172

BioStudentx

Original post by BanterBus

alow m8 just allow it, for this spec we dont need to know Lewis acids, take it to another thread.

Original post by alow

Clearly you do, because if not you won't be able to understand these equilibria.

Looks like we've memorised it and not understood it. Oh dear. I have no clue what Lewis acids are or why it's accepting electrons or how this relates to equilibria. Lets hope they just add a normal acid or a normal base, like a normal person...

Reply 3173

BanterBus

Original post by lai812matthew

it accepts an electron pair so it is a lewis acid. i'm not sure if they ask for lewis acids and bases in exam????? it is in the book's blue boxes.

If it's in the blue boxes, knowing OCR it's bound to be a 6 marker. We're screwed.

Reply 3174

alow

Original post by BioStudentx

It's the same as using AlCl₃ as a halogen carrier, where the Lewis acid (AlCl₃) accepts an electron pair from a halide.

Reply 3175

Dinasaurus

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+".

The question just said magnesium, they added magnesium.

Reply 3176

Dinasaurus

Question 6a for the June 15 paper http://stsmith.co.uk/data/documents/F325-01-QP-Jun15.pdf

How the F325 am I supposed to know which is more negative?