Calculate The Ph of A 0.150 M Solution of Koh

Potassium hydroxide (KOH) is a strong base that completely dissociates in water. Calculating its pH involves understanding the relationship between concentration and pH for strong bases. This calculator provides an accurate pH value for a 0.150 M KOH solution and explains the underlying chemistry.

Introduction

The pH of a solution measures its acidity or basicity on a scale from 0 to 14. For strong bases like KOH, the pH can be calculated directly from the concentration using the following relationship:

pH = 14 + log[OH⁻]

Where [OH⁻] is the concentration of hydroxide ions in moles per liter (M).

Since KOH is a strong base, its concentration of hydroxide ions equals its molarity. For a 0.150 M KOH solution, [OH⁻] = 0.150 M.

How to Calculate the pH

Step 1: Determine the hydroxide ion concentration

For strong bases, the concentration of hydroxide ions ([OH⁻]) is equal to the molarity of the base. For KOH:

[OH⁻] = [KOH] = 0.150 M

Step 2: Calculate the pH using the hydroxide ion concentration

Use the pH formula for strong bases:

pH = 14 + log[OH⁻]

Substitute [OH⁻] = 0.150 M into the equation:

pH = 14 + log(0.150)

Step 3: Perform the logarithmic calculation

Calculate log(0.150) using a calculator:

log(0.150) ≈ -0.8169

Step 4: Final pH calculation

Add the logarithmic result to 14:

pH = 14 + (-0.8169) = 13.1831

The pH of a 0.150 M KOH solution is approximately 13.18.

Worked Example

Let's calculate the pH of a 0.150 M KOH solution step by step:

Identify that [OH⁻] = [KOH] = 0.150 M
Use the formula: pH = 14 + log(0.150)
Calculate log(0.150) ≈ -0.8169
Final pH = 14 + (-0.8169) = 13.18

The calculation shows that a 0.150 M KOH solution has a pH of approximately 13.18, indicating it is strongly basic.

Interpreting Results

A pH of 13.18 for a 0.150 M KOH solution indicates:

The solution is strongly basic
It contains a high concentration of hydroxide ions
It would neutralize acids completely
It would turn red litmus paper blue

Note: The pH calculation assumes the solution is at standard temperature (25°C) and that KOH is a complete strong base.

FAQ

Why does KOH have a pH of 13.18 at 0.150 M?

KOH is a strong base that completely dissociates in water, so its hydroxide ion concentration equals its molarity. The pH formula for strong bases gives pH = 14 + log[OH⁻], resulting in 13.18 for 0.150 M KOH.

What happens if the KOH concentration changes?

Increasing the KOH concentration increases the hydroxide ion concentration, lowering the pH further. Decreasing the concentration raises the pH. The relationship is logarithmic.

Is this calculation valid for all temperatures?

The calculation assumes standard temperature (25°C). At other temperatures, the pH may change slightly due to temperature effects on dissociation constants.