What is the pH of 2 M aluminium nitrate ?

1 Answer
May 17, 2017

Answer:

#sf(pH=2.62)#

Explanation:

The ion undedrgoes hydrolysis:

#sf([Al(H_2O)_6]^(3+)rightleftharpoons[Al(H_2O)_5OH]^(2+)+H^+)#

You should be given #sf(pK_a)# for this. My Cotton and Wilkinson gives #sf(pK_a=4.95)#.

For a weak acid a quick way to get the pH is to use the expression:

#sf(pH=1/2[pK_a-loga]#

Where a is the initial concentration of the solution.

#:.##sf(pH=1/2[4.95-(-0.3)])#

#sf(pH=2.62)#

Small, highly charged cations like this tend to be quite acidic.