Question

the ph of pure water
the ph of pure water is ____ because ____.

multiple choice

○ 14.0; water contains more oh⁻ ions than h⁺ ions

○ 7.0; water contains an equal number of h⁺ ions and oh⁻ ions

○ 5; because pure water lacks minerals

○ 1.0; water contains more h⁺ ions than oh⁻ ions

○ 7.0; there are no ions formed in pure water

Explanation:

• For the first option: A pH of 14.0 is basic, but pure water is neutral. Also, in pure water, $[\ce{H^+}] = [\ce{OH^-}]$, so it's incorrect.
• For the second option: Pure water is neutral with a pH of 7.0. In pure water, the auto - ionization reaction $\ce{H2O <=> H^+ + OH^-}$ produces equal concentrations of $\ce{H^+}$ and $\ce{OH^-}$ ions (at 25°C, $[\ce{H^+}] = [\ce{OH^-}] = 1\times10^{- 7}\ \text{M}$), so this is correct.
• For the third option: A pH of 5 is acidic, and the lack of minerals has no relation to the pH of pure water. Pure water's pH is determined by ion concentrations, so this is incorrect.
• For the fourth option: A pH of 1.0 is strongly acidic, and in pure water, $\ce{H^+}$ and $\ce{OH^-}$ concentrations are equal, so this is incorrect.
• For the fifth option: Pure water does ionize (auto - ionize) to form $\ce{H^+}$ and $\ce{OH^-}$ ions, so the statement "there are no ions formed in pure water" is false.

Answer:

B. 7.0; water contains an equal number of $\boldsymbol{H^+}$ ions and $\boldsymbol{OH^-}$ ions