Forming acids and alkalis

Soluble metal oxides (or metal hydroxides) produce alkaline solutions.Soluble non-metal oxides produce acidic solutions.

Insoluble oxides will not affect the pH of water.

Example one

What will happen to the pH of water if barium oxide is added?

Using the databook we find that barium oxide is a metal oxide. Checking its solubility on page 8 of the databook we see that it will dissolve. It is therefore a soluble metal oxide and it will increase the pH.

Example two

What will happen to the pH of water if sulfur dioxide is added?

Using the databook we find that sulfur dioxide is a non-metal oxide. We know it is soluble because it contributes to acid rain. It is therefore a soluble non-metal oxide and it will decrease the pH.

Example three

What will happen to the pH of water if aluminium oxide is added?

Using the databook we find it is a metal oxide. Checking its solubility on page 8 we find it is insoluble.It will therefore have no effect on the pH of water.