Degree of ionisation
Tutorial 3
Calculation of the degree of ionization of acids and bases
Definition of degree of ionization
$\alpha $ $ = $ $ \frac{number \; of\;dissociated\; moles \; by\; protolysis} {number \; of\; initially\; present\; moles } $
Example:
If $\alpha $ of a weak acid is $ 0.2 $, this means that from 100 molecules of this acid initially introduced into the medium 20 have formed hydronium ions and the corresponding base.
Determination of degree of ionization
1) For strong acids and bases:
$\alpha = 1 $
2) For weak acids:
A) Look for $ [H_3O^+] $ (see here ):
B) Find the initial molarity $ c_0 $
C) Then $\alpha = \frac{H_3O^+}{c_0} $
3) For weak bases:
A) Look for $ [OH^-] $ (see here ):
B) Find the initial molarity $ c_0 $
C) Then: $\alpha = \frac{OH^-} {c_0} $
Calculate the degree of ionization of a $ 0.010 \; M $ solution of cyclohexylamine $ (pK_a = $ 10.64)!
First find $[OH^-]$ !
For answers, use (possibly several times) the arrows ↑ Down! and ↓ Up!
Complete please this question before moving on to the next one!
$\alpha$ $=$ $\frac{OH^-}{c_0}$ $=$ $\frac{2.09\cdot 10^{-3} }{0.010}$ $=$ $0.21$
