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Buffer solutions

Hi, I'm just a bit confused ATM...

If we have a basic buffer solution which is composed of ammonia solution and ammonium chloride solution, what reactions occur to restore the pH when acid is added and when alkali is added?

Thanks :smile:
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Reply 2
Avatar for Borek
Borek
4
Original post by lulu1997
If we have a basic buffer solution which is composed of ammonia solution and ammonium chloride solution, what reactions occur to restore the pH when acid is added and when alkali is added?


First of all - in what forms is ammonia present in the buffer solution? Which of these is an acid and which is a conjugate base?
Original post by lulu1997
Hi, I'm just a bit confused ATM...

If we have a basic buffer solution which is composed of ammonia solution and ammonium chloride solution, what reactions occur to restore the pH when acid is added and when alkali is added?

Thanks :smile:


Add alkali: shift of equilibrium position, hence retainment of pH
Add acid, increased [salt], hence equilibrium shift to alkali again to resist change

Le Chatalier. Simple.
Reply 4
Avatar for Borek
Borek
4
Original post by Infraspecies
Add alkali: shift of equilibrium position, hence retainment of pH


Add acid: shift of equilibrium position, hence retainment of pH

You have just won this week's contest for the most useless answer.
Reply 5
Avatar for lulu1997
lulu1997
OP
1
Sorry I didn't make it clear - it's a basic buffer so the weak base is ammonia solution and the soluble salt of its conjugate acid is ammonium chloride solution (the ammonium ion is the conjugate acid)... I was just wondering what exact reactions occur which lead to the pH being restored. I got confused because I saw two sources stating different things.
Original post by Borek
Add acid: shift of equilibrium position, hence retainment of pH

You have just won this week's contest for the most useless answer.


What a bad put down.
Reply 7
Avatar for Borek
Borek
4
Original post by lulu1997
Sorry I didn't make it clear - it's a basic buffer so the weak base is ammonia solution and the soluble salt of its conjugate acid is ammonium chloride solution (the ammonium ion is the conjugate acid)... I was just wondering what exact reactions occur which lead to the pH being restored. I got confused because I saw two sources stating different things.


First of all: it is not that "pH is being restored". pH does change when you add an acid or base to the buffer. Thing is: it doesn't change by as much as it would be the case there were no buffer present.

The reactions taking place are those you know: when you add an acid (H+) ammonia gets protonated, when you add a base (OH-), it reacts with NH4+ producing ammonia. In each case added H+or OH- is consumed and doesn't change pH directly. It shifts the equilibrium in the solution, slightly changing pH - but just by a tiny amount.
Reply 8
Avatar for Komandor
Komandor
Hi I know Borek has explained it already and made it clear (mate I am gonna ask you if I ever have chemistry problems, you're like a walking knowledge!) but maybe those could help you too:
http://www.scienceclarified.com/A-Al/Acids-and-Bases.html
http://www.elmhurst.edu/~chm/vchembook/184ph.html
http://www.chemguide.co.uk/physical/acidbaseeqia/buffers.html

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