Question

Water softeners remove metal ions such as Ca²⁺ and Fe³⁺ by replacing them with enough Na⁺ ions to maintain the same number of positive charges in the solution. If 5.5*10³ L of hard water is 0.015 M Ca²⁺ and 0.0010 M of Fe³⁺ , how many moles of Na⁺ are needed to replace these ions?

Answer 1

moles of Ca+2 ions = 5.5 x 10^3 x 0.015

                                = 82.5 mol

1 mol Ca+2 required -------------> 2 mol Na+ to neutralize

82.5 mol Ca+2           -------------->   ??

moles of Na+ required = 165 mol

165 mol Na+ are needed to replace Ca+2 ions

moles of Fe+3 ions = 0.0010 x 5.5 x 10^3

                               = 5.5 mol

moles of Na+ ions = 5.5 x 3 = 16.5 mol Na+

16.5 mol Na+ ions needed to replace Fe+3 ions