Water superheated under pressure to 200 °C and 750 atm has Kw = 1.5 * 10-11. What is 3H3O+ 4 and 3OH-4 at 200 °C? Is the water acidic, basic, or neutral?

Key Concepts

Ion Product of Water (Kw)

The ion product of water (Kw) is the equilibrium constant for the self-ionization of water, defined as Kw = [H3O+][OH-]. At 25 °C, Kw is typically 1.0 x 10^-14, but it varies with temperature. At higher temperatures, such as 200 °C, Kw increases, indicating a higher concentration of hydronium and hydroxide ions in pure water.

Acidic, Basic, and Neutral Solutions

A solution is considered acidic if [H3O+] > [OH-], basic if [H3O+] < [OH-], and neutral if [H3O+] = [OH-]. The pH scale, which ranges from 0 to 14, helps classify solutions: pH < 7 indicates acidity, pH > 7 indicates basicity, and pH = 7 indicates neutrality. Understanding the relationship between hydronium and hydroxide ion concentrations is crucial for determining the nature of the solution.

Temperature Effects on pH

Temperature affects the dissociation of water and the values of Kw, which in turn influences the pH of the solution. As temperature increases, the dissociation of water becomes more favorable, leading to higher concentrations of both H3O+ and OH-. This means that at elevated temperatures, the neutral point shifts, and the pH of pure water can be above 7, indicating that the water may not be neutral at high temperatures.