Final answer:
To calculate the hydroxide ion concentration at 25 °C when the hydrogen ion concentration is given, use the ion product constant of water to find [OH−]. The hydroxide ion concentration is determined by dividing the constant (1.0 × 10−14) by the hydrogen ion concentration (12.7 x 10−6), resulting in a hydroxide concentration of 7.87 × 10−9 M.
Step-by-step explanation:
The question asks to find the hydroxide ion concentration, [OH−], in a solution when the hydrogen ion concentration, [H+], is 12.7 x 10−6 M at 25 °C. To solve this problem, we use the ion product constant for water at 25 °C, which is Kw = 1.0 × 10−14. This constant represents the product of the concentrations of hydrogen ions and hydroxide ions in water.
To find the hydroxide ion concentration, the formula is Kw = [H+][OH−]. Since we have the value of [H+], we can rearrange the formula to solve for [OH−]:
[OH−] = Kw / [H+].
Substituting in the known values gives us:
[OH−] = (1.0 × 10−14) / (12.7 x 10−6).
After performing the division, the hydroxide ion concentration comes out to be [OH−] = 7.87 × 10−9 M.