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Question #25ba6

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Oct 14, 2017

The alkalinity is due to the phosphate ion, $P O_{4}^{3 -}$ $PO_4^(3-)$ . Details follow.

Explanation:

The phosphate ion has a limited ability to gain $H^{+}$ $H^+$ (they bond to the lone pairs of the O atoms in the $P O_{4}^{3 -}$ $PO_4^(3-)$ ion).

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

$H_{2} O + P O_{4}^{3 -} \to H P O_{4}^{2 -} + O H^{-}$ $H_2O+PO_4^(3-) rarr HPO_4^(2-) + OH^-$

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

This changing of $H_{2} O$ $H_2O$ into $O H^{-}$ $OH^-$ is called hydrolysis and is responsible for the solution becoming basic.

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