Question

Waste water from a cement factory contains 0.25 g of Ca2+ and 0.056 g of Mg2+ per 100.0 L of solution. The solution density is 1.001 g/mL. Calculate the Ca+2 and Mg +2 concentrations in ppt, ppm and ppb (by mass)

Answer 1

The mass of 100L waste water solution is

(100L solution)×$\frac{1ml}{10^{-3}L}$ ×$\frac{1.001g}{1ml}$ = 1.001×10⁵ g

ppt = $\frac{mass of solute}{mass of solution}$ × 10¹²

Ca²⁺ ppt = $\frac{0.25}{1.001×10^5}$ ×10¹² = 2.5×10⁶ ppt

Mg²⁺ ppt = $\frac{0.056}{1.001×10^5}$ × 10¹² = 5.6×10⁵ ppt

ppm = $\frac{mass of solute }{mass of solution}$ ×10⁶

Ca²⁺ ppm = $\frac{0.25}{1.001×10^5}$ ×10⁶ = 2.5 ppm

Mg²⁺ ppm = $\frac{0.056}{1.001×10^5}$ × 10⁶ = 0.56 ppm

ppb = $\frac{mass of solute }{mass of solution}$ ×10⁹

Ca²⁺ ppb = $\frac{0.25}{1.001×10^5}$ ×10⁹ = 2.5 × 10³ ppb

Mg²⁺ ppb = $\frac{0.056 }{1.001×10^5}$ ×10⁹ = 5.6×10² ppb