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Writing Net ionic equations

  1. Mar 14, 2005 #1
    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
    Last edited: Mar 14, 2005
  2. jcsd
  3. Mar 15, 2005 #2


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    I'm guessing that e.g.

    [tex]H_3PO_4_{(g)} + H20_{(l)} \xrightarrow~3H_3O^{+}_{(aq)} + PO_4^{-3}_{(aq)} [/tex]
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