1) Cheap electricity is essential for the commercial viability of an aluminium smelter.

a) Calculate the electric charge required to produce 0.500 kg of alluminium from alumina in Hall-Heroult cell.

Al³⁺_{(in cryolite)} + 3e => Al_(l)

Step 1 convert 0.500 kg of aluminium to mol.
=> 500.00 / 26.98 =18.53

Step 2 calculate the amount of electrons in mol
18.53 X 3 = 55.6

Step 3 calculate the charge
55.6 X 96,500 = 5,367,000 C

b) How long must a current of 150,000 A flow in order to deposit 1.00 tonne(10⁶g ) of aluminium?

Step 1 convert 10⁶g of aluminium to mol.
=> 10⁶ / 26.98 = 3.70 X 10⁴

Step 2 calculate the mol of electrons needed
=> 3 X 3.70 X 10⁴ =1.11 X 10⁵

Step 3 calculate the charge this represents
=> 1.11 X 10⁵ X 96,500 = 1.07 X 10¹¹ C

Step 4 calculate the time in seconds taken to deliver this charge at acurrent of 150,000 A
=> Q = I X t(sec)
=> t(sec) = Q/I =1.07 X 10¹¹ / 150,000
=> t(sec) = 7.1 X 10⁵

c) What is the mass of carbon consumed at the anodes if a cell operates at 150,000 A for 2.00 hours?

Al³⁺_{(in cryolite)} + 3e => Al_(l)

According to the equation above we require 3 mol of electrons to porduce 1 mol of aluminium.
Step 1 calculate the mol of electrons
=> Q = I X t(sec) = 150,000 X 2 X 60 X 60 = 1.1 X 10⁸
=> 1.1 X 10⁸ / 96,500 =1.14 X 10³

Step 2 calculate the mole of aluminium produced
1.14 X 10³ / 3 = 380

Step 3 calculate the mole of carbon used

2Al₂O_{3(in cryolite)} + 3C_(s) => 4Al_(l) + 3CO_2(g)

=> 3/4 X 380 = 285

Step 4 calculate the mass of carbon
285 X 12 = 3.42 kg

d) How does an aluminium smelter contribute to global warming?

Production of carbon dioxide and use of high amounts of electrical energy which may also cause the generation of carbon dioxide at the power station if it is not a hydroelectric power station or other renewable energy source.

e) What is the mass of carbon dioxide produced per day by an aluminium smelter producing 1,000 tonnes of aluminium per day?

2Al₂O_{3(in cryolite)} + 3C_(s) => 4Al_(l) + 3CO_2(g)

Step 1 convert 10⁹ grams of Aluminium into mol
=> 10⁹ grams / 26.98

Step 2 find the mol of carbon dioxide produced according to the equation above.
=> 3.71 X 10⁷ X 3/4 = 2.78 X 10⁷

Step 3 find the mass of carbon dioxide.

2.78 X 10⁷ X 44 =1.2 X10⁹ grams