Given a selection of anions, phosphate, sulfate, nitrate, how do we form salts with cations?

1 Answer
Dec 6, 2016

You have to know the charge on the constituent ion, and then these combine in such a way to form a NEUTRAL salt.

Explanation:

So we we've got a selection of anions, say $P {O}_{4}^{3 -}$, $S {O}_{4}^{2 -}$, and ${P}^{3 -}$. You simply have to know these species as common ions.

And now, these make music with a selection of common CATIONS, $C {a}^{2 +}$, $F {e}^{3 +}$, $N {a}^{+}$. Now all matter is electrically neutral, so when these ions combine, they do so in a way as to make the overall electric charge $0$, i.e. the salt is NEUTRAL. Are we clear on this? If no, voice your objections, and we will have another go.

So with phosphate ion, $P {O}_{4}^{3 -}$, we would form $C {a}_{3} {\left(P {O}_{4}\right)}_{2}$, $F e \left(P {O}_{4}\right)$, and $N {a}_{3} \left(P {O}_{4}\right)$. All I have done here is to cross-multiply to give an ionic salt in which negative and positive charges are EQUAL such that the charge on the SALT is neutral.

And with sulfate, we get $C a S {O}_{4} , F {e}_{2} {\left(S {O}_{4}\right)}_{3} , N {a}_{2} S {O}_{4}$.

You try this, and make neutral salts with the phosphide anion, ${P}^{3 -}$. I grant that this appears abstract, but all we are doing is making sure that the ionic solid is NEUTRAL. Again, come back for another serve if you don't see it.