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.