10. Acids and Bases

Chemistry student prepared an aqueous solution at 30ºC. If the solutions contains 7.42 × 10⁻⁹ M of hydroxide ions, calculate the pH.

Calculate the K_w of pure water given the pH = 6.34.

How is K_w defined, and what is its numerical value at 25 °C?

The dissociation of water into H₃O⁺ and OH^– ions depends on temperature. At 0 °C the [H₃O⁺] = 3.38 x 10^–8 M, at 25 °C the [H₃O⁺] = 1.00 x 10^–7 M, and at 50 °C the [H₃O⁺] = 2.34 x 10^–7 M.

c. Is the dissociation of water endothermic or exothermic?

The dissociation of water into H₃O⁺ and OH^– ions depends on temperature. At 0 °C the [H₃O⁺] = 3.38 x 10^–8 M, at 25 °C the [H₃O⁺] = 1.00 x 10^–7 M, and at 50 °C the [H₃O⁺] = 2.34 x 10^–7 M.

b. What is the value of K_w at 0 °C and 50 °C?