G-chem question

[UnimaasMED]

I have 2 questions:

1) What is the cathode in the following reaction?

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


please include the steps for determining the oxidation state. Thanks!

2) when we want to determine how many electrons are involved in production of Gold as given by AU2+ + 3e -> AU , how do I know that its 3e and not 2? Would I have to memorize that the half-rxn?

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[UndergradGuy7]

1) What is the cathode in the following reaction?

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

Anode is oxidation and cathode is reduction.

PbO2 has 2 x 2- O = -4, so Pb is +4.
Pb(s) = 0
PbSO4 has SO4^2-, so Pb is +2.

Reduction is+4 to +2.
PbO2 -> PbSO4
more complete... since right side has SO4^2- and left side is missing it...
PbO2 + SO4^2- -> PbSO4 and then add the H2O's and H+'s to balance it and electrons. This would be the total half reaction at the cathode.

not sure if you need all of that or just wanted the PbO2 -> PbSO4 part.


2) when we want to determine how many electrons are involved in production of Gold as given by AU2+ + 3e -> AU , how do I know that its 3e and not 2? Would I have to memorize that the half-rxn?

Think it is a typo the Au^2+ should be Au^3+. Then Au^3+ + 3e- -> Au uses 3 electrons. It says 3e- in the equation.

 

[chromosome21]

there must be a typo for #2

 

[UnimaasMED]

Thanks for replying. But how do I know that Gold produces a 3+ cation? I mean Gold has 1 valence electron right?

 

[UndergradGuy7]

Thanks for replying. But how do I know that Gold produces a 3+ cation? I mean Gold has 1 valence electron right?

I don't think you will ever get a question asking what type of cation a transition metal forms. Some transition metals can form more than one type of cation.

You will be given the equation telling you what cation it makes.