Acid-base equilibria
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Hi, I was just wondering why is it that a mixture of hydrochloric acid and sodium chloride not act as a buffer solution?
Corrie writes . . .
A buffer solution contains a mixture of a weak acid (e.g. ethanoic acid) and its conjugate base (ethanoate ion). In a buffer solution the following equilibrium is establihed:
HA(aq) <=> H+(aq) + A-(aq) - - - (where HA = weak acid)
There are significant amounts of both HA and A- present at equilibrium. Thus, if acid or alkali is added to the buffer solution, this equilbrium can move in either direction to absorb the added H+ or OH-ions.
In a HCl/NaCl mixture in solution the HCl, being a strong acid, will be completely or almost completely (depending on the NaCl concentration). The corresponding equilibrium to the one above will lie almost completey over to the right.
So although there will H+ ions to react with any base added, the Cl- ions present will be too weak a base to remove any H+ ions added to the buffer.
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updated: 16 March 2007
