What mass of Al would be obtained from the complete reduction of 10.2 tonnes of Al2O3?

5.4 tonnes.

Explanation:

The first step is to find the molar mass of Al2O3. Aluminum has a molar mass of about 27 and oxygen has a molar mass of about 16, so 2(27)+3(16)= 102g/mol=0.102kg/mol. 10200kg/0.102kg/mol=100,000 moles of Al2O3 in 10.2 tonnes. Multiplying this by the molar mass of the two aluminums, you get a total of 54*100,000=5400000g=5400kg=5.4 tonnes. Hope this helps!