Final answer:
Pure water has a neutral pH of 7.00, due to the equal concentrations of hydronium and hydroxide ions, each being 1 × 10^-7 M at 25 °C.
Step-by-step explanation:
The pH of pure water is a measure of its acidity or alkalinity. In pure water at 25 °C, the concentration of hydronium ions (H3O+) is very low, with only about 1 in 10 million water molecules dissociating to form hydronium ions. Consequently, pure water is presumed neutral, with a pH of 7.00, which is the midpoint of the pH scale that ranges from 0 to 14. The neutrality of pure water is due to the equal concentrations of hydronium and hydroxide ions (OH-), both being 1 × 10-7 moles per liter at 25 °C, which results in a pH of 7.00 when calculated using the formula pH = -log [H+].
It's worth noting that while temperature variations can affect the concentration of hydronium ions in water, the solution remains neutral because [H+] and [OH-] remain equal, like at 40 °C where both [H3O+] and [OH-] are different from 25 °C but still equal to each other, maintaining neutrality.