Deuterium oxide 1D2O, where D is deuterium, the hydrogen-2 isotope) has an ion-product constant, Kw, of 8.9 * 10-16 at 20 °C. Calculate 3D+4 and 3OD-4 for pure (neutral) D2O at this temperature.
Ch.16 - Acid-Base Equilibria
Chapter 16, Problem 120
At 50 °C, the ion-product constant for H2O has the value Kw = 5.48 * 10-14. (a) What is the pH of pure water at 50 °C? (b) Based on the change in Kw with temperature, predict whether ΔH is positive, negative, or zero for the autoionization reaction of water: 2 H2O1l2 Δ H3O+1aq2 + OH-1aq2

Verified Solution
Video duration:
4m
Was this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Ion-Product Constant of Water (Kw)
The ion-product constant of water (Kw) is the equilibrium constant for the autoionization of water, represented by the equation 2 H2O ⇌ H3O+ + OH-. At any given temperature, Kw is the product of the concentrations of hydronium ions [H3O+] and hydroxide ions [OH-]. For pure water, these concentrations are equal, allowing us to calculate the pH based on the value of Kw.
Recommended video:
Guided course
Solubility Product Constant
pH Scale
The pH scale is a logarithmic scale used to measure the acidity or basicity of a solution. It is defined as pH = -log[H3O+], where [H3O+] is the concentration of hydronium ions in moles per liter. In pure water, the pH is typically 7 at 25 °C, but this value changes with temperature due to variations in Kw, affecting the concentrations of H3O+ and OH-.
Recommended video:
Guided course
The pH Scale
Temperature Dependence of Kw
The value of Kw changes with temperature, generally increasing as temperature rises. This is indicative of the endothermic nature of the autoionization reaction of water. If Kw increases with temperature, it suggests that the reaction absorbs heat, leading to a positive ΔH. Understanding this relationship helps predict how pH and ion concentrations will shift with temperature changes.
Recommended video:
Guided course
Kw Temperature Dependence
Related Practice
Textbook Question
2283
views
Textbook Question
The indicator methyl orange has been added to both of the following solutions. Based on the colors, classify each statement as true or false: (a) The pH of solution A is definitely less than 7.00.
672
views
Textbook Question
The probe of the pH meter shown here is sitting in a beaker that contains a clear liquid. You are told the liquid is pure water, a solution of HCl(aq), or a solution of KOH(aq). (b) If the liquid is one of the solutions, what is its molarity?
1099
views
Textbook Question
The probe of the pH meter shown here is sitting in a beaker that contains a clear liquid. (c) Why is the temperature given on the pH meter?
358
views