More questions...

A couple question...

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I was just wondering about the oxidation number. example: PH3 P has 3+ and H has 1- so all you need to do is subract the two or do i have the method wrong. thanks
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I'd start from the other direction on this, hydrogen is almost always oxidation number +1, so if there are 3 hydrogens at +1, and the molecule is neutral overall, then the phosphorus must be oxidation number -3.

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I was doing one of the "Conceptual Exercise" problems and can't figure out how they came up with the answer that they did. It is 5.4 on page 175 part B. I came up with H^+ + OH^- yields H_2_0. It looks like that is the answer but then it has another equation for an answer as well. I know I am forgetting something simple but I can't figure out what it is and it's driving me nuts. Please help me out and thanks in advance.
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These are a bunch of acid-base net ionic equations, so I'll address them all.

HCl(aq) + KOH(aq) --> H₂O(l) + KCl(aq)
H⁺(aq) + Cl^-(aq) + K⁺(aq) + OH^-(aq) --> H₂O(l) + K⁺(aq) + Cl^-(aq)
Chloride ions and potassium ions don't change, so they are spectators and the net ionic equation is:
H⁺(aq) + OH^-(aq) --> H₂O(l)

H₂SO₄(aq) + Ba(OH)₂(aq) --> 2 H₂O(l) + BaSO₄(s)
This one should look familiar...
2 H⁺(aq) + SO₄^2-(aq) + Ba²⁺(aq) + 2 OH^-(aq) --> 2 H₂O(l) + BaSO₄(s)
Since water is a molecule and barium sulfate is a precipitate, these both stay together in the full ionic equation, so the net ionic equation doesn't have any spectator ions here...
2 H⁺(aq) + SO₄^2-(aq) + Ba²⁺(aq) + 2 OH^-(aq) --> 2 H₂O(l) + BaSO₄(s)

CH₃COOH(aq) + NaOH(aq) --> H₂O(l) + NaCH₃COO(aq)
You could also represent acetic acid and acetate ions as CH₃CO₂H/CH₃CO₂^- or HC₂H₃O₂/C₂H₃O₂^-. Acetic acid is a weak acid, so it should not be split up in the ionic equation:
CH₃COOH(aq) + Na⁺(aq) + OH^-(aq) --> H₂O(l) + Na⁺(aq) + CH₃COO^-(aq)
The sodium ion is a spectator, so the net ionic is:
CH₃COOH(aq) + OH^-(aq) --> H₂O(l) + CH₃COO^-(aq)

Other questions, let me know, I'll be checking email all evening. I'll also post answers first thing in the morning. Good luck...