Determine the pH of a solution that is 3.85% KOH by mass. Assume that the solution has density of 1.01 g/mL.

Verified step by step guidance

1. Calculate the mass of KOH in 100 g of solution using the percentage by mass: \( \text{mass of KOH} = 3.85\% \times 100 \text{ g} \).
2. Determine the volume of the solution using its density: \( \text{volume} = \frac{100 \text{ g}}{1.01 \text{ g/mL}} \).
3. Calculate the molarity of the KOH solution: \( \text{molarity} = \frac{\text{moles of KOH}}{\text{volume of solution in liters}} \).
4. Since KOH is a strong base, it dissociates completely in water: \( \text{KOH} \rightarrow \text{K}^+ + \text{OH}^- \). The concentration of \( \text{OH}^- \) is equal to the molarity of KOH.
5. Calculate the pH using the relation: \( \text{pH} = 14 - \text{pOH} \), where \( \text{pOH} = -\log[\text{OH}^-] \).

Key Concepts

pH Scale

The pH scale measures the acidity or basicity of a solution, ranging from 0 to 14. A pH of 7 is neutral, values below 7 indicate acidity, and values above 7 indicate basicity. The pH is calculated as the negative logarithm of the hydrogen ion concentration in the solution, which is crucial for understanding the solution's chemical behavior.

KOH Dissociation

Potassium hydroxide (KOH) is a strong base that completely dissociates in water into potassium ions (K+) and hydroxide ions (OH-). This complete dissociation means that the concentration of hydroxide ions directly influences the pH of the solution. Understanding this dissociation is essential for calculating the resulting pH from the concentration of KOH in the solution.

Concentration Calculations

To determine the pH of the KOH solution, one must first calculate its molarity, which involves converting the mass percentage to grams per liter using the solution's density. This calculation allows for the determination of the hydroxide ion concentration, which is then used to find the pH. Mastery of concentration calculations is vital for accurately assessing the properties of solutions in chemistry.