Acid properties of salts

Some salts exhibit properties making solutions acid when the salt is dissolved in water. E.g., the following reaction takes place when NH4CI is dissolved in water  

The last reaction is an acid-base reaction and we shall look at how pH is calculated in such a solution in the following example  

We wish to determine pH in a 0.01 M solution of AICI3. It has been observed that when aluminium chloride is dissolved in water an acid solution is the result. Even though the Af ion is not an acid itself as it cannot produce a ion, it is the so-called hydrate compound A1(H20)6 that is a weak acid reacting with water in the following maimer  

The aluminium-ion will thereby in aqueous solution be surrounded by 6 water molecules. The Ka value for A1(H20)6 is 1.4 10 M. Again we will start by looking at the main components in the solution. These are in this case  

On the basis of the reaction scheme above we have the following equilibrium expression  

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