Example 2

₂(SO_cuatro)_{step three}, is an ionic compound that is used in the manufacture of paper and in various water purification processes. What is the formula mass (amu) of this compound?

Solution The formula for this compound indicates it contains Al 3+ and SO₄ 2? ions combined in a 2:3 ratio. For purposes of computing a formula mass, it is helpful to rewrite the formula in the simpler format, Al₂S₃O_several. Following the approach outlined above, the formula mass for this compound is calculated as follows:

Check Your Learning Calcium phosphate, Ca₃(PO₄)₂, is an ionic compound and a common anti-caking agent added to food products. What is the formula mass (amu) of calcium phosphate?

Answer:

The identity of a substance is defined not only by the types of atoms or ions it contains, but by the quantity of each type of atom or ion. […]