Question

If 1.5 moles of oxygen combine with Al to form Al2O3,the mass of Al in g used in the reaction is

Answer 1

4Al + 3O2 ---> 2Al2O3 
1mole O2 = 32g * 1.5mole = 48g * 2 = 96g 
Al2O3 = 101.96g/mole * 2 = 203.92g 
203.92g - 96g O2 = 107.92g. 
Therefore, 
The weight of Al in the reaction of 1.5moles of O2 is 107.92g

Answer 2

Answer: 54 g

Explanation: $4Al+3O_2\rightarrow 2Al_2O_3$

According to the balanced equation:

3 moles of oxygen combine with= 4 moles of aluminium

Thus 1.5 moles of oxygen combine with=$\frac{4}{3}\times 1.5=2moles$ of aluminium

Mass of aluminium= ${\text {number of moles}}\times {\text {Molar mass of aluminium}}=2\times 27g/mol=54g$