Buffer buffetting (1 Viewer)

[Undermyskin]

It is said that buffer solution works best within a narrow range of pH. What does it mean by this optimal range? Does it mean that to reach this ideal pH, we are supposed to add the amount of one major component more than the other. For example, NH3 more than NH4Cl to reach a certain basic pH? Otherwise I can't think of any other way to create an optimal pH for a buffer solution since they are commonly weak acids and their conjugate bases which are moderately weak as well. So unless one is supplied more than the other, we can never get that optimal pH, right?

Can anyone confirm?

 

[cameron0110]

I assume the optimal pH depends on whether you are buffering against acid/base or both. For example, if you added a lot of a weak base, e.g. sodium acetate, to act as a buffer and then added something like sodium hydroxide to the solution then the buffer would have virtually no effect because barely any acetic acid would be present to neutralise it. On the other hand it would work very well if you added a strong acid because the acid would have to protonate all the sodium acetate before any free H+ would be floating around in solution.

Is that what you meant?

 

[Undermyskin]

Er.... I don't think so. OK, I'd better summarize my question.

How to create an optimal pH for a buffer solution?

Just my idea: add one of the two component more than the other or equal depending on the pH we want to create. But I'm not so sure.

 

[xiao1985]

Doubt you'll need to know this, but buffering works best when the pH is close to the pKa of the weak acid you are using. ie, NH3 / NH4)+ works best around pH 9 etc

 

[Undermyskin]

pKa... pKa... pKa... is it the one we study in Industrial Chem? I think I'm wrong. Is it the division of [] products by reactants? Er... Can you tell me how to do it? I think I forget so much.

 

[brenton1987]

pKa... pKa... pKa... is it the one we study in Industrial Chem? I think I'm wrong. Is it the division of [] products by reactants? Er... Can you tell me how to do it? I think I forget so much.

HA --> H⁺ + A^-
K_a = ([H⁺] [A^-]) / [HA]
pK_a = -log₁₀ K_a

It is equal to the pH at which the molecules deprotonate.

For example
H₃PO₄ --> H₂PO₄^- + H⁺ pK_a1 = 2.15
Below pH 2.15 the species H₃PO₄ will dominate while between pH 2.15 and 7.20 (When the next dissociation occurs) the species H₂PO₄^- will dominate.

Acid Dissociation Constant

 

[Undermyskin]

Thanks.