How Do You Write Net Ionic Equations for These Reactions?

[vsage]

The directions say to give the net ionic equation for the principal reaction. I did the first couple right (I think) but don't know how to proceed: (the part by the number is the question and my answer is 2 spaces below)

1. NH4Ac(aq) + HCl(aq) -> ?

H+ + AC- -> HAc

2. NH4F(s) + HCl(aq) -> ?

NH4F(s) + H+ -> F-(aq) + NH4+(aq)

3. (NH4)2SO4(aq) + H2CO3(aq) -> ?

Don't know, H2CO3 is a weak acid but I don't know whether to write it on the products side as a weak acid or write it in ion form. Sulfates are soluble in water so that should break up into its ions

4. H2S(aq) + NH3(aq) (excess) -> ?

I don't know the signifiance of (excess). H2S is a weak acid so I once again don't know how to write it in a net ionic equation.

5. H3PO4(aq) + NH3(aq) (excess) -> ?

Since phosphates are soluble in water when combined with group 1 elements, I guessed that it breaks up into its ions yielding the equation H+(aq) + NH3(aq) -> NH4+(aq)

6. H3 PO4(aq) (excess) + NH3(aq) -> ?

I don't know why excess would make it any different. So basically what I'm asking through these questions is

a. What does an excess of one reactant have to do with anything?
b. Are weak acids written on both sides of the equation in molecular (as opposed to ionic) form? Thanks

 

[wais]

a. An excess of one reactant means that there is more of that reactant present than needed for the reaction to occur. It does not change the overall reaction, but it may affect the amount of products formed.
b. Weak acids can be written in both molecular and ionic form in a net ionic equation. It depends on the specific reaction and what is being emphasized. In general, it is more common to write weak acids in their ionic form in net ionic equations.