General Chemistry Ii Jasperse - Electrochemistry Extra Practice Problems With Answers Page 12
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Electrolysis: Key Equations: Mol e
–
= [A • time (sec)/96,500]
time (sec)= mol e • 96,500/current (in A)
62. Copper metal (63.546 g/mol) is purified by electrolysis. How much copper metal (in grams) could be produced from
copper(II) oxide by applying a current of 10.0 amps at the appropriate negative potential for 12.0 hours?
T
Time and Amps to Grams Problems:
a.
284 g
d.
14.2 g
1. Use Amps and Time to fine moles of electrons
b.
142 g
e.
4.48 g
2. Find "n": moles of electrons per mole of metal
c.
28.4 g
3. Using "n", convert from moles e's to moles metal
4. Using formula weight, can convert between
moles of metal and grams of metal
63. How long would it take to electroplate a flute with 28.3 g of silver (107.87 g/mol) at a constant current of 2.0 amps
using AgNO
?
3
a.
211 min
d.
1688 min
Grams to Time Problems given Amps:
1. Using formula weight, convert grams metal => moles metal
b.
422 min
e.
105 min
2. Find "n", and convert moles metal => moles electrons
c.
844 min
3. Give moles of e's and amps => time (in seconds)
4. Convert seconds to actual time units (min, hours...)
64. How many grams of aluminum metal (26.982 g/mol) can be produced by the electrolysis of Al
O
using a current of
2
3
100 amperes for 24 hours?
13
a.
805
d.
2.2 × 10
12
b.
2,400
e.
7.5 × 10
5
c.
8.1 x 10
T
65. If in using a lead-acid battery to start a car, 1.00 gram of Pb (207.2 g/mol) is consumed on the anode, how long will it
take to recharge the battery, using a current of 0.500 amperes to turn the PbSO
that was produced back into Pb?
4
a.
15.5 min
d.
21 min
b.
1864 min
e.
42 min
c.
31 min
66. Chromium often is electroplated on other metals and even plastics to produce a shiny metallic appearance. How many
grams of chromium (51.996 g/mol) would plate out from a solution of Cr(NO
)
when 10 amps of current are passed
3
3
through the electrolytic cell for 5.36 hours?
a.
17.3 g
d.
104 g
b.
34.7 g
e.
11.6 g
c.
52.0 g
T
67. Suppose an aluminum (26.982 g/mol) beer can weighs 40.0 g. For how long would a current of 100.0 amp need to be
passed through a molten AlF
electrolysis cell to produce enough aluminum to replace a discarded beer can?
3
a.
4.44 hr
d.
42.7 min
b.
23.8 min
e.
2.38 hr
c.
1.19 hr
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