What is the pH of 2 M aluminium nitrate ?

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Answer 1 · 2017-05-17T18:44:22

#sf(pH=2.62)#

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.