A weak acid has a pKa of 4.435. If the solution pH is 4.72, what percentage of the acid is dissociated?How do you calculate percentage of acid when it is undissociated?
Assuming this is a monoprotic acid (if it's di- or tri-protic, you'll need to use an alpha fraction equation), then you can simply set up an ICE table, where you're looking at a Ka equation. Since you know the pH of the solution, you know [H3O+] and you can use an the ICE table to find the concentration of the undissociated (HA) form. You know that the concentration of A- and H3O+ must be the same, so you only have one unknown.
For example...
HA . + . H20 ... --%26gt; A- ... + ... H3O+
x ......... -- ... ... 10^(-pH) ... 10^(-pH)
Ka = ([A-][H3O+])/([HA])
Now that you know both [A-] and [HA], you should be able to calculate the fraction of dissociation.
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