Question

Question #25ba6

Answer 1

The alkalinity is due to the phosphate ion, `PO_4^(3-)` . Details follow.

Explanation:

The phosphate ion has a limited ability to gain `H^+` (they bond to the lone pairs of the O atoms in the `PO_4^(3-)` ion).

When this happens in aqueous solution, the `H^+` are taken from molecules of water as follows:

`H_2O+PO_4^(3-) rarr HPO_4^(2-) + OH^-`

That is, the water molecule is pulled apart, such that one piece is `H^+` and the other is `OH^-`.

This changing of `H_2O` into `OH^-` is called hydrolysis and is responsible for the solution becoming basic.