How to Calculate pH and [OH⁻] in Chemistry?

What is the pH of a solution with [H₃O⁺] = 3.0 × 10⁻⁴ M?

a) 4.52 b) 3.0 × 10⁻⁴ M c) 4.0 × 10⁻³ M d) 5.26

What is the [OH⁻] of a solution when the pH is 9.0?

a) 1.0 × 10⁻⁹ M b) 1.0 × 10⁻⁵ M c) 1.0 × 10⁻³ M d) 1.0 × 10⁻⁷ M

Answer:

1. The pH of a solution with [H₃O⁺] = 3.0 × 10⁻⁴ M is 3.52.

2. The [OH⁻] of a solution with pH 9.0 is 1.0 × 10⁻⁵ M.

Chemistry can be a daunting subject, especially when it comes to calculating pH and [OH⁻] concentrations in a solution. However, it doesn't have to be! Understanding these concepts can be fun and exciting.

pH Calculation:

pH is a measure of the acidity or alkalinity of a solution. It is calculated using the formula: pH = -log[H₃O⁺]. In the first question, when [H₃O⁺] = 3.0 × 10⁻⁴ M, by substituting the value into the formula, we get pH = -log(3.0 × 10⁻⁴) = 3.52.

[OH⁻] Calculation:

The [OH⁻] concentration can be derived from the pH of a solution using the relation: [H₃O⁺] × [OH⁻] = 1 × 10⁻¹⁴. By taking the antilog of the negative pH value, we can determine the [OH⁻] concentration. In the second question, when the pH is 9.0, the [OH⁻] concentration is therefore 1.0 × 10⁻⁵ M.