Buffer solution دکتر امید رجبی دانشیار گروه شیمی دارویی. شیمی عمومی. Buffer solutions are solutions that resist change in Hydronium ion and the hydroxide ion concentration (and consequently pH ) upon addition of small amounts of acid or base , or upon dilution. .
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
A buffer solution
CH3COONa CH3COO- + Na+
CH3COOH + H2O CH3COO- + H3O+
small amount Large amount
CH3COOH + OH- CH3COO- + H2O
CH3COO- + H3O+ CH3COOH + H2O
Weak acid + H2O H3O+ + Conjugate base
Ka = [H3O+][conjugate base]
[H3O+] = Ka x [weak acid]
pH = -log [H3O+]
The weak acid H2PO4- in a blood buffer H2PO4-/HPO42- has Ka = 6.2 x 10-8. What is the pH of the buffer if it is 0.20 M in both H2PO4- and HPO42-?
[H3O+] = Ka x [H2PO4-]
[H3O+] = 6.2 x 10-8 x [0.20 M] = 6.2 x 10-8
pH = -log [6.2 x 10-8] = 7.21
Let's begin our discussion of the Henderson-Hasselbach Equation with a continuation of the dissociation constant derivation.
should be a familiar relationship . If we rearrange our equation to provide the [H3O+] on the left side, we get
[H3O+] =Ka (HA)/(A-)
(Notice that the ionized species of the acid is now in the denominator.)
Taking the negative log of both sides gives us easier numeric values to work with:
which can be rewritten
more familiarly numeric values to work with: