Question

How many moles of O2- ions are there in 0.450 moles of aluminum oxide, Al2O3?

Answer 1

Answer:

                     1.35 moles of O²⁻

                     21.6 grams of O²⁻

Explanation:

We know that the charge on Aluminium ion is +3 (i.e. Al³⁺) while, the charge on Oxide ion is -2 (i.e. O²⁻). Therefore, the overall neutral Al₂O₃ compound has 2 Al³⁺ ions and 3 O²⁻ ions. Since, we can say that,

                 1 mole of Al₂O3 contains  =  3 moles of O²⁻ ions

So,

                     0.450 moles of Al₂O₃ will have  =  X g of O²⁻

Solving for X,

                      X =  0.450 mol × 3 mol ÷ 1 mol

                     X =  1.35 moles of O²⁻

As the mass of an atom is mainly due to the presence of protons and neutrons hence, the addition of two electrons (-ve 2 shows two gained electron) to Oxygen will make a negligible change to the atomic masss of Oxygen because electron is said to be almost 1800 times lighter than proton. Hence, the ionic mass of O²⁻ will be 16 g/mol and the mass of given moles is calculated as,

                     Mass  =  Moles × Ionic Mass

                     Mass  =  1.35 mol × 16 g/mol

                    Mass  =  21.6 g