A sample of water has hardness expressed as 1.6 × 10² ppm Ca²⁺(aq).The sample is passed through an ion exchange column and the Ca²⁺(aq)ions are replaced by H⁺(aq)ions.What is the pH of the water after it has been treated? (1 ppm = 1 g solute/10⁶ g solution)

Question

Quizplus · Accepted Answer

The pH of the water after treatment is determined by the concentration of H+ ions introduced by the ion exchange process. The hardness of the water, 1.6 × 10^12 ppm, translates to 1.6 × 10^-4 g of Ca^2+ per gram of water. Since the molar mass of Ca^2+ is approximately 40 g/mol, this corresponds to 4 × 10^-6 moles of Ca^2+ per liter of water. The ion exchange replaces Ca^2+ with 2 moles of H+ for each mole of Ca^2+, resulting in 8 × 10^-6 moles of H+ per liter. The pH is calculated using the formula pH = -log[H+], which gives pH = -log(8 × 10^-6) = 2.09.

A Sample of Water Has Hardness Expressed as 1