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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: zoork34 on November 17, 2006, 05:53:01 PM

Title: amount of protonated species from pKa and pH
Post by: zoork34 on November 17, 2006, 05:53:01 PM

Ok, if i have a .1 M solution of a compound, say, diethylamine, with pKa of about 11, and i put it in water and raise the pH up and down, is there any way i can say exactly how much DEA i have at each pH?  i know from the henderson-hasselbalch equation i can get the ratio of protonated to non-protonated, but i dont know how to get the actual amounts. 

Title: Re: amount of protonated species from pKa and pH
Post by: Borek on November 17, 2006, 05:59:13 PM

http://www.chembuddy.com/?left=pH-calculation&right=pH-polyprotic-acid-base

See equations 9.11, 9.12 & 9.13 for a hint.

Note: if you have a single proton acid/base, you can use K_a (K_b) definition and [HA] + [A^-] = C_a (mass balance) to setup system of two equations in two unknowns - once solved it will give you needed answer.