Does Polyprotic Strong Acid Completely Dissociate in a Net Ionic Equation?

[apchemstudent]

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 I am 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

 

[GCT]

I'm guessing that e.g.

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

 

[ravenprp]

In net ionic equations, we assume that all strong acids and bases completely dissociate in water. This means that for polyprotic strong acids like H3PO4 and H2SO4, we would write the net ionic equation as the complete dissociation of the acid into its respective ions, as you have correctly done for the reactions involving sulfuric acid.

For the reaction between aluminum chloride and sulfuric acid, the net ionic equation would be Al(3+) + 3Cl(-) + 3H(+) + 3SO4(2-) -> Al(3+) + 3SO4(2-) + 3H(+) + 3Cl(-). This may seem like everything cancels out, but it is still important to include all ions in the equation to show the complete dissociation of the acid and the formation of the products.

Your net ionic equation for the reaction between calcium and water is correct. As you mentioned, calcium hydroxide is a strong base and therefore completely dissociates in water, resulting in the formation of calcium ions and hydroxide ions.

For the reaction between calcium hydroxide and ammonium phosphate, your net ionic equation is also correct. The hydroxide ions remain on the reactant side to balance out the ionic charges, but they are still considered to be in their ionic form.

In the reaction between sulfuric acid and magnesium hydroxide, both of your proposed net ionic equations are correct. The first one, H+ + HSO4(-) + 2OH(-) -> SO4(2-) + 2H2O, shows the complete dissociation of the acid into its ions, while the second one, HSO4(-) + OH(-) -> SO4(2-) + H2O, shows the formation of water from the combination of a hydrogen ion and a hydroxide ion. Both are valid ways of writing the net ionic equation for this reaction.

Finally, your net ionic equation for the reaction between phosphoric acid and magnesium hydroxide is also correct. It shows the complete dissociation of the acid and the formation of the products.

Overall, it is important to remember that in net ionic equations, we assume complete dissociation of strong acids and bases. This may result in seemingly simple equations, but it is important to include all ions in order to accurately represent the