# Writing Net ionic equations

I have to write net ionic equations for reactions. I have a big question to ask about polyprotic strong acids. Do we assume that the acid completely dissociates in a net ionic equation, such as H3PO4 and H2SO4?

aluminum chloride + sulfuric acid -> aluminum sulfate + hydrogen chloride

I got 3HSO4(-) -> 3SO4(2-) + 3H(+)
If i assumed H2SO4 completely dissociates then there wouldn't be a net ionic equation. Everything cancels out.

Calciuim + water -> calcium hydroxide + H2

I got Ca + 2H2O -> Ca(2+) + 2OH(-) + H2

Is this correct? I'm using a chart that says calcium hydroxide is soluble so that's why they are in ionic form.

Calcium hydroxide + ammonium phosphate -> calcium phosphate + ammonia + water

3 Ca(+) + 6 OH(-) + 6NH4(+) + 2PO4(3-) -> Ca3(PO4)2 + 6NH3 + 6H2O
I think this is correct. In a book i have, they kept the hydroxide ion on the reactant side, instead of removing a hyroxide ion from both sides.

sulfuric acid + Magnesium hydroxide -> magnesium sulfate + water
This is another one i have problems on.
Again im using a book that says that MgOH is soluble(my teacher's book)

H+ + HSO4(-) + 2OH(-) -> SO4(2-) + 2H2O

Is this it? I mean, a hydroxide ion and a hydrogen ion can combine to form water in the reactant, so that

HSO4(-) + OH(-) -> SO4(2-) + H2O

So I'm not sure which one is correct.
Again, the complete dissociation question.... the net ionic can also be 2 H(+) + 2 OH(-) ->2 H2O

Which one is the correct one?

As well, phosphoric acid + magnesium hydroxide -> magnesium phosphate + water

6 H(+) + 2 PO4(3-) + 3 Mg(2+) + 6 OH(-) -> Mg3(PO4)2 + 6H2O

Again, is this correct? .... Please help thanks

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## Answers and Replies

GCT
Science Advisor
Homework Helper
I'm guessing that e.g.

$$H_3PO_4_{(g)} + H20_{(l)} \xrightarrow~3H_3O^{+}_{(aq)} + PO_4^{-3}_{(aq)}$$