6th edition, 14.5d

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Hai-Lin Yeh 1J
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6th edition, 14.5d

Postby Hai-Lin Yeh 1J » Wed Feb 27, 2019 9:21 pm

Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in basic solution. Identify the oxidizing agent and reducing agent in each reaction.
(d) Reaction of elemental phosphorus to form phosphine, PH3, a poisonous gas with the odor of decaying fish:
P4 (s) -> H2PO2 - (aq) + PH3 (g)
How do you write the oxidation half-reaction and reduction half reaction for d?

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Re: 6th edition, 14.5d

Postby Chem_Mod » Sat Mar 02, 2019 6:14 am

So for the reduction half reaction, you start with P4 --> PH3, and here are the steps to go through to balance it.
1. Balance the P's: P4 --> 4PH3
2. Balance the H's using H2O and OH- since we are working in a basic solution: P4 + 12H2O --> 4PH3 + 12OH-
3. Balance the charges: P4 + 12H2O + 12e- --> 4PH3 + 12OH- (since you have 12 negative charges on the right from the OH-, you have to add 12 electrons to the left side)

So for the oxidation half reaction, you start with P4 --> H2PO2-, and here are the steps to go through to balance it.
1. Balance the P's: P4 --> 4H2PO2-
2. Balance the H's using H2O and OH- since we are working in a basic solution: P4 + 8OH- --> 4H2PO2-
3. Balance the charges: P4 + 8OH- --> 4H2PO2- +4e- (since you have 8 negative charges on the left from the OH-, you have to add 4 electrons to the right side)


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