Masses or Volumes from Electrolysis.
A unit of electrical
charge is called a Coulomb.
One Coulomb (symbol Q) is 6·2 x 1018 electrons.
One mole of electrons
is the same as 96,500 Coulombs.
96,500 Coulombs is called a Faraday.
(symbol I) is a flow of electrical
The rate of flow of electrical charge is measured in amps (A).
One amp is one Coulomb per second. Q = I x t.
The electrolysis of molten lead bromide - PbBr2
produces lead at the cathode and bromine at the anode.
A current of 10 amps is
allowed to flow
through molten lead bromide for 5 hours.
What mass of lead is deposited at the cathode?
1) Write the half equation for the electrolysis.
Pb2+ + 2e- Pb
2 moles of electrons (2 Faradays)
are required to deposit 1 mole of lead.
2) Find how many Faradays have passed through
the lead bromide in 5 hours.
Q = I x t
hours contains (5 x
60 x 60)
= 18,000 seconds.
10 x 18,000
= 180,000 Coulombs.
Faraday = 96,500 coulombs.
180,000 coulombs = 180,000 ÷ 96,500 Faradays
= 1·865 Faradays.
3) From the
proportion in 1 above,
2 Faradays are required to deposit 1 mole of lead.
1·865 faradays will deposit (1·865 ÷ 2) moles of lead,
= 0·933 moles of lead.
mass = moles x RAM
RAM of lead = 207
= 0·933 x 207
= 193 g of lead.
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