How many moles of o2- ions are there in 0.350 moles of aluminum oxide, al2o3?

The formula for aluminum oxide is Al2O3, which means that, if aluminium oxide is ionically bonded, every formula mass of aluminum oxide contains three O2- ions. In this instance, .0350 formula masses of aluminum oxide would contains, 0.350 mole Al2O3 (3 mole O2-/1mole) = 3*0.350 = 1.05 Hence 1.05 moles of O2-. If aluminum oxide were covalently bonded, it would not contain any O2- ions.

There are 1.05 moles of O²⁻ in 0.350 moles of Al₂O₃.

FURTHER EXPLANATION The chemical formula of a compound consists of the chemical symbol of the elements that make up the compound and a small number written to the right of the symbol or the subscript. The subscript indicates how many atoms or ions of that element is found in one unit (formula unit or molecule) of the compound. It also indicates how many moles of the atom or ion are present in one mole of the compound.  Example, the chemical formula of calcium chloride is CaCl₂. This can be interpreted in two ways:

              1) There is one Ca²⁺ and and two Cl⁻ in one   formula

                  unit of calcium chloride.

             2)There is one mole of Ca²⁺ and and two moles of Cl⁻ in

                one mole of calcium chloride.

It is important to remember that the mole concept considers particles in bundles (or sacks) with one mole being one bundle (or sack) which consists of 6.022 ×10²³ particles. This number is called Avogadro's number.  The particles may be atoms, ions, molecules, or formula units.

The compound in the problem is Al₂O₃. Similar to the example, this chemical formula can be interpreted in two ways:

There are 2 aluminum ions (Al³⁺) and 3 oxide ions (O²⁻) in one formula unit of Al₂O₃.There are 2 moles of aluminum ions (Al³⁺) and 3 moles of oxide ions (O²⁻) in one mole of Al₂O₃.

To determine how many moles of O²⁻ are in 0.350 moles of Al₂O₃, the equation below may be used:

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Keywords: moles, mole ratio

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