Posted on May 18, 2025 by Quiz of the Day #1. The ion-product constant for water at 45 °C is 4.0 x 10–14. What is the pH of pure water at this temperature? 6.7 7.0 7.3 13.4 The ion-product constant Kw for water is Kw = [H+][OH–] The definition of pH is pH = -log[H+] Previous Check Answer Results Click the “Quiz” button for a new question