Question

A sample of pure water contains

A. a smaller concentration of H3O+ ions than OH- ions.

B. a larger concentration of H3O+ ions than OH- ions.

C. equal concentrations of OH- and H3O+ ions.

D. neither OH- ions nor H3O+ ions.

Answer 1

In pure water, the concentrations of hydronium (H₃O⁺) ions and hydroxide (OH⁻) ions are equal, making the water neutral. The concentration of both ions is 1.0 × 10⁻⁷ M.

Step-by-step explanation:

The question is about the concentration of hydroxide (OH⁻) ions and hydronium (H₃O⁺) ions in a sample of pure water. In pure water, these ions exist in equilibrium, and their concentrations are equal. Pure water autoionizes into equal numbers of hydrogen (H⁺) ions, which immediately combine with water molecules to form hydronium ions (H₃O⁺), and hydroxide (OH⁻) ions. The concentration of hydronium and hydroxide ions in pure water is about 1.0 × 10⁻⁷ M, meaning a sample of pure water contains equal concentrations of OH⁻ and H₃O⁺ ions, which makes the water neutral.

Based on this information, the correct answer to the student's question is:
C. equal concentrations of OH⁻ and H₃O⁺ ions.

Answer 2

The answer is c because it is helpful to understand the balance between these two ions. An aqueous solution is a solution in which water is the solvent. Water molecules (H2O) are polar, meaning that they have a negative end (the oxygen) and a positive end (the hydrogens). When there is a reaction in an aqueous solution, the water molecules have the ability to attract and temporarily hold a donated proton (H+). This creates the hydronium ion (H3O+).