Chad GEN CHEM QUESTION!

[ramonsanjose]

I am going over electrochemistry right now and I am having some trouble understanding question 2 of chad's quiz on electrochemical cells (7.2).

What is the cathode of the reaction?

PbO2 (s) + Pb (s) + 2H2SO4 (aq) ---> 2PbSO4 (s) + H2O (l)

The answer is that PbO2 is the cathod.

K I get that the oxidation states of Pb in PbO2 = +4 and Pb(s) = 0
What I do not understand is that Pb in 2PbSO4 (s) = +2

Can someone give me some incite?

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[jhc83]

SO4 is a polyatomic ion with a charge of -2. This would make Pb +2..... but since there is a 2 infront of Pb, you would double the charge, which makes Pb to be +4. In total, +4 minus -2 = +2. I hope that helps!

 

[ramonsanjose]

Ahh! I forgot it was polyatomic. Thanks jhc!