Question

Which of the following has the lowest OH- concentration (or highest hydrogen ion concentration)?

Answer 1

The concentration of hydronium ion in the solution determines the pH and acidity of the solution.

Step-by-step explanation:

The concentration of hydronium ion in a solution of an acid in water is greater than 1.0 × 10-7 M at 25 °C. The concentration of hydroxide ion in a solution of a base in water is greater than 1.0 × 10-7 M at 25 °C. The concentration of H3O* in a solution can be expressed as the pH of the solution; pH = -log H₂O+. The concentration of OH can be expressed as the pOH of the solution: pOH = -log[OH-]. In pure water, pH = 7.00 and pOH = 7.00

Answer 2

The substance with the lowest OH⁻ concentration, indicating the highest hydrogen ion concentration, is the one with the lowest pOH value. Therefore, the solution with the lowest pOH value has the highest hydrogen ion concentration.

Step-by-step explanation:

In a solution, the concentrations of hydrogen ions (H⁺) and hydroxide ions (OH⁻) are related through the ion product of water, Kw, which is equal to [H⁺] × [OH⁻].

The pOH is the negative logarithm (base 10) of the hydroxide ion concentration, and it is related to the pH by the equation: pOH = 14 - pH. In this context, a lower pOH value corresponds to a higher concentration of OH⁻ ions.

For example, consider two solutions with pOH values of 2 and 4. The solution with a pOH of 2 has a higher OH⁻ concentration because 10⁻² (from the pOH value) is greater than 10⁻⁴ (from the pOH value of 4).

Consequently, the solution with the lower pOH value has the higher OH⁻ concentration and, by extension, the higher concentration of H⁺ ions. This reflects a more acidic solution, as pH and pOH are inversely related.

In summary, the solution with the lowest pOH value will have the highest concentration of hydrogen ions (H⁺) and the lowest concentration of hydroxide ions (OH⁻), making it the most acidic among the options.