Cr from molten CrO_3 Aluminum is produced commercially by the electrolysis of Al

Question

Cr from molten CrO_3 Aluminum is produced commercially by the electrolysis of Al_2O_3 in the presence of a molten salt. If a plant has a continuous capacity of 1.00 million A, what mass of aluminum can be produced in 2.00 h? An unknown metal M is electrolyzed. It took 74.1 s for a current of 2.00 A to plate out 0.107 g of the metal from a solution containing M(NO_3)_3. Identify the metal. Electrolysis of an alkaline earth metal chloride using a current of 5.00 A for 748 s deposits 0.471 g of metal at the cathode. What is the identity of the alkaline earth metal chloride? What volume of F_2 gas, at 25 degree C and 1.00 atm, is produced when molten KF is electrolyzed by a current of 10.0 A for 2.00 h? What mass of potassium metal is produced? At which electrode does each reaction occur? What volumes of H_2(g) and O_2(g) at STP are produced from the electrolysis of water by a current of 2.50 A in 15.0 min? A single Hall-Heroult cell (as shown in Fig. 18.22) produces about 1 ton of aluminum in 24 h. What current must be used to accomplish this? A factory wants to produce 1.00 times 10^3 kg barium from the electrolysis of molten barium chloride. What current must be applied for 4.00 h to accomplish this? It took 2.30 min using a current of 2.00 A to plate out all the silver from 0.250 L of a solution containing Ag^+. What was the original concentration of Ag^+ in the solution? A solution containing Pt^4+ is electrolyzed with a current of 4.00 A. How long will it take to plate out 99% of the platinum in 0.50 L of a 0.010 M solution of Pt^4+? A solution at 25 degree C

Explanation / Answer

Step 1

Write the reduction reaction between metal and predict the mol ratio between metal and electrons.

M(NO3)3 + 3 e- --- > M(s)

Since 1 mol metal needs 3 mol electrons

Mol ratio between M and electrons is 1 : 3

Step 2

Find the moles of metal using Current , coulomb time and Faradays constant relation relation.

Current ( amp) = C (coulomb) / s

F = faradays constant ( 96500 C/mol of electrons )

Mol Metal = Coulomb x ( 1 mol e- / 96500 C) x ( 1 mol M / 3 mol e-)

Since C = I x t , we can substitute this equation for coulomb

Mol metal = 2.0 A x 74.1 s x ( 1 mol e- / 96500 C ) x ( 1 mol M / 3 mol e-)

=0.00051 mol M

Step 3

Use

Mol = mass in g / molar mass , to find molar mass of metal

Molar mass = mass in g / mole of M = 0.107 g / 0.00051 mol M

=209.0

209 is molar mass of Po

So the metal is Polonium.

Question number 99

Step 1

Write reduction reaction and predict mol ratio between Ag and electrons.

Ag+ + 1 e- --- > Ag(s)

Mol ratio is 1:1

Step 2

Find out moles of Ag

Moles of Ag

= ( 2.00 A x 2.30 min x 60 s /1 min) x (1 mol e-/ 96500 C) x (1mol Ag+ / 1 mol e-)

=4.76684E-05 mol Ag +

Step 3

Calculate its original concentration

[Ag+] = mol Ag+ / volume in L

= 4.76684E-05 / 0.25 L

= 1.91 E-4 M

Ans : [Ag+]= 1.91 E-4 M

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