Chromium metal can be electroplated from an acidic solution of (CrO 4 ) -2 a. Wr
ID: 908308 • Letter: C
Question
Chromium metal can be electroplated from an acidic solution of (CrO4)-2
a. Write the half reaction
b. Determine the equivalent weight of Cr.
c. What mass of Cr, in grams, will be deposited by a current of 98.54 C?
d. What mass of Cr, in grams, will be deposited by a current of 3.0 amps passing for 4 minutes?
e. How many minutes will it take for 1.5 grams of Cr to be deposited by a current of 1.2 amps?
f. How many Faradays of electricity are required to deposit 52 grams of Cr.?
Explanation / Answer
CrO4^-2 oxidation state of Cr = +6
CrO4-2 + 8H+ + 6e- -----------------------> Cr (s) + 4H2O
(a) half -reaction :
CrO4-2 + 8H+ + 6e- -----------------------> Cr (s) + 4H2O
(b) equivalent weight = molar mass / 6
= 51.996 /6
= 8.666 g
(c)
What mass of Cr, in grams, will be deposited by a current of 98.54 C?
q = 98.54 C
Faraday law
W = E x i x t / F
= E x q / F
W = 8.666 x 98.54 / 96500
W = 0.0088g
mass of Cr = 0.0088g
(d)
What mass of Cr, in grams, will be deposited by a current of 3.0 amps passing for 4 minutes
W = E x i x t / 96500
= 8.666 x 3 x 4 x 60 / 96500
= 0.0647 g
weight of Cr = 0.0647 g
e.) How many minutes will it take for 1.5 grams of Cr to be deposited by a current of 1.2 amps?
W = E x i x t / 96500
1.5 = 8.666 x 1.2 x t / 96500
t = 13919.339 seconds
t = 232 minutes
f. ) How many Faradays of electricity are required to deposit 52 grams of Cr.
6 Faradays are needed