A sample of water has hardness expressed as 1.6 × 10² ppm Ca²⁺. The sample is passed through an ion exchange column and the Ca²⁺ ions are replaced by H⁺ ions. What is the pH of the water after it has been treated? (1 ppm = 1 g solute/106 g solution) A) 2.09 B) -.80 C) 1.10 D) 7.00 E) 2.40

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The concentration of Ca²⁺ ions is 1.6 × 10² ppm, which is equivalent to 1.6 × 10^-4 M. When replaced by H⁺ ions, the concentration of H⁺ ions will also be 1.6 × 10^-4 M. The pH is calculated as -log[H⁺], which gives a pH of approximately 2.09.

A Sample of Water Has Hardness Expressed as 1