Question

How many coulombs are required to plate a layer of chromium metal 0.29 mm thick on an auto bumper with a total area of 0.25 m2 from a solution containing CrO2−4? The density of chromium metal is 7.20 g/cm3.

Express your answer using two significant figures.

Q =

nothing

C

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Part B

What current flow is required for this electroplating if the bumper is to be plated in 12.5 s ?

Express your answer using two significant figures.

Answer 1

a) thickness = 0.29 mm = 0.029 cm

Area = 0.25 m^2 = 2500 cm^2

Volume of chromium required= area*thickness = 0.029*2500

= 72.5 cm^3

Mass of chromium required= density*volume = 7.2*72.5 = 522g

Mass of 1 mol of chromium= 52g

Number of moles in 522 g = 522/52 = 10.038 moles

In (CrO4)2-, chromate ion has a charge of +6. This implies that 6 electrons are needed to reduce each Cr+6 ion to Cr.

1 mole of Cr+6 ions needs 6 moles of electrons. 10.038 moles of Cr+6 needs 6*10.038 = 60.23 moles of electrons.

60.23*6.02*10^23 = 3.625*10^25 electrons.

1 coulomb is approximately the magnitude of 6.24151*10^18 times the charge on an electron.

Number of Coulombs = 3.625*10^25/6.24151*10^18 = 5.807*10^6 C

Answer: 5.807*10^6 C

b) 1 ampere = 1 Coulomb per second

5.807*10^6 C should be delivered in 12.5 seconds

Current = Coulimb/second = 5.807*10^6/12.5 = 4.6456*10^5 A

Answer: 4.6456*10^5A