Help with gchem question

[creative8401]

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hi everyone, a quick question

If electricity costs 0.10/coulomb, which is most expensive to liberate electrolysis?

A)Au2S3
B)AuC
C)PtCl2
D)AgOH
E)PtCl4

Ok, the answer is E b/c Cl4 is -4, so Pt would require 4, but the answer explanation says that AuC is Au+, isnt carbon -4, how in the world did they make it to be -1 so that Au would require only one electron?

 

[drgreen]

I've never heard of AuC either.

Maybe since Au by itself is short 1 electron of a full "d" sub-shell, it takes one electron from elemental carbon leaving it as 1s2-2s2-3s2-3p1 with a charge of +1, then there is an ionic association. I guess it makes sense. Metal-Nonmetal is characteristic of ionic bonding.