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A level chemistry buffers help please

I’m confused why for weak acid buffers, when a small amount of OH- is added, it reacts with some of the tiny amount of H+ ions instead of the many undissociated HA acid molecules?

For weak alkali buffers (e.g NH3 and NH4Cl), if H+ is added my textbook says it reacts with the many NH3 molecules, not the OH- ions. So why is it different?

Thanks!!
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Kim J
13
i don know either looks like
(edited 2 years ago)
Original post by Mavs04
I’m confused why for weak acid buffers, when a small amount of OH- is added, it reacts with some of the tiny amount of H+ ions instead of the many undissociated HA acid molecules?

For weak alkali buffers (e.g NH3 and NH4Cl), if H+ is added my textbook says it reacts with the many NH3 molecules, not the OH- ions. So why is it different?

Thanks!!

There is no reason for a hydroxide ion to react with an HA molecule. The HA molecule is neutral and stable (relatively). The negative charge on the hydroxide ion (lone pair of electrons) is attracted strongly to the positive hydrogen (hydronium) ions.

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