Buffers and Equilibria context

I also have another question: the dissociation of an acid HA is endothermic, what effect will this have on the Ka if the concentration of the acid increased. I thought that because it's more concentrated, more H+ dissociated, so the conc of products becomes greater, therefore Ka because bigger. But the answer is no change.

Sorry, I mean NaOH

To what?

ammonia?

Only one thing affects equilibrium constants and that's temperature ...

I'm going to start again.

If we wanted to form a buffer solution say with a weak acid, I can add NaOH to CH3COOH which means I will have a salt of the acid (sodium ethanoate) and a weak acid (ethanoic acid)

Now let's say we want to make a buffer with a weak base. I can add NH3 with HCl to form NH3Cl which is a salt of my weak base. Why can I not do this?


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You can (although ammonium chloride is actually NH₄Cl) provided the weak base is in excess ..

Is that to prevent further substitution reactions?


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No, it's because a basic buffer consists of a weak base and the salt of a weak base ...

... is all.

Only one thing affects equilibrium constants and that's temperature ...

Does this mean, say if I was titrating a weak acid with NaOH, despite the volume added of NaOH and the pH rise, the Ka will still stay the same


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Ka is a constant. That means that it doesn't change.

Only one thing affects equilibrium constants and rate constants (which are related) and that's temperature ...

Thanks! I think I understand the context of buffers really well now!

I'm stuck on one part of the context: If we have a strong acid, is the concentration of H+ the SAME as the concentration of the acid (or) is the concentration of H+ makes up most of the concentration of the acid meaning that there is literally 0moldm-3 of the acid ITSELF in the solution?

Also, is the concentration of A- the same as that of H+?

So if we had a strong acid and 95% was dissociated, would this mean we have 95% concentration of H+ and A- EACH?



Last question, kW is ALWAYS 1.00x10-14 at 298K, but varies at different temperatures. BUT water nevertheless has the same H+ and OH- concentration.

yes,it is the same as the stated original acid concentration

and yes, there are no acid molecules left in the solution.





yes





yes

yes,it is the same as the stated original acid concentration

and yes, there are no acid molecules left in the solution.





yes





yes

Is a buffer essentially formed at the half-neutralisation point between a weak acid and NaOH? Is this a 2:1?

Why is it said that we need "excess" acid and a strong base?

Easy peasy way of losing a mark.

Buffers do not keep pH constant, they minimise pH changes on addition of small amounts of an acid or a base.