Problems A
315
PROBLEM:
What current is required to plate out 0.0200 mole of gold from a AuCl 3 solution
in 3.00 hr?
SOLUTION:
From the half-cell reaction
\ Au
3+ + e- -* $ Au
we can see that a mole of Au
3+ contains 3 E-T equivalents. Thus,
E-T equiv of Au = (0.0200 mole Au) ( 3
equlv | = 0.0600 equiv Au
\ mole/
Because 0.0600 equiv Au requires 0.0600 faraday of electricity for plating out,
amperes =
coulombs
seconds
(0.0600 faraday) ( 96,487
coulombs\
faraday /
(3hr)
Hfr)
= 0.536 amp required
PROBLEMS A
1. One-half faraday of electricity is passed through aqueous solutions of the
compounds listed in the following table. Both electrodes are made of the
material indicated. In the appropriate places in the table, give the formula
of the substance that is produced at each electrode, and the amount that
is produced. If a solid is produced, express the amount in moles; if a gas is
produced, express the amount in liters (dry) at standard conditions.
Compound
NiSO 4
Cal 2
Fe(N0 3 ) 3
Au(CI0 4 ) 3
LiHC0 3
Electrode
material
Ni
Pt
stainless
steel
Au
Cu
Negative electrode
Substance
produced
Amount
produced
Positive electrode
Substance
produced
Amount
produced