posted by Vic on .
In terms of a buffer solution, can one exist with a strong acid and of weak base in equal volumes but different molarities? e.g. 0.1 HCl and 0.2 NH3? I found this to be the case but still can't find a logical reasoning behind it.
Sure there is, if you really think about it.
HCl + NH3 ==> NH4Cl
Remember that a buffer solution is formed with a weak acid and its conjugate base (such as acetic acid and sodium acetate) OR a weak base and its conjugate base (such as NH3 and NH4Cl). What you have done is to add 0.2 M NH3 to 0.1 M HCl (and I assume it was done so that the mols NH3 exceeded the mols HCl), so you have formed the salt, NH4Cl, and you have an excess of NH3. Bingo, you have a buffered solution.