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Calculate The Ph of 0.05 M Naoh Solution

Reviewed by Calculator Editorial Team

Sodium hydroxide (NaOH) is a strong base that completely dissociates in water to produce hydroxide ions (OH⁻). The pH of a NaOH solution can be calculated using the concentration of hydroxide ions and the pH formula. This guide explains how to calculate the pH of a 0.05 M NaOH solution and interpret the results.

Introduction

The pH of a solution is a measure of its acidity or alkalinity. For strong bases like NaOH, the pH can be calculated directly from the concentration of hydroxide ions. The pH scale ranges from 0 to 14, where values below 7 are acidic, 7 is neutral, and values above 7 are alkaline.

When NaOH dissolves in water, it dissociates completely according to the equation:

NaOH (aq) → Na⁺ (aq) + OH⁻ (aq)

The concentration of hydroxide ions ([OH⁻]) in a 0.05 M NaOH solution is equal to the concentration of NaOH because the dissociation is complete. The pH is then calculated using the pH formula for hydroxide ions:

pH = 14 + log[OH⁻]

This formula is derived from the fact that the product of [H⁺] and [OH⁻] in water is always 10⁻¹⁴ at 25°C.

How to Calculate the pH of NaOH Solution

To calculate the pH of a NaOH solution, follow these steps:

  1. Determine the concentration of NaOH in moles per liter (M).
  2. Since NaOH is a strong base, the concentration of hydroxide ions ([OH⁻]) is equal to the concentration of NaOH.
  3. Use the pH formula for hydroxide ions: pH = 14 + log[OH⁻].
  4. Calculate the pH using a calculator or logarithmic functions.

For a 0.05 M NaOH solution:

[OH⁻] = 0.05 M pH = 14 + log(0.05) pH ≈ 14 - 1.3010 ≈ 12.6990

The pH of a 0.05 M NaOH solution is approximately 12.70.

Example Calculation

Let's calculate the pH of a 0.05 M NaOH solution step by step.

  1. Given: [NaOH] = 0.05 M
  2. Since NaOH is a strong base, [OH⁻] = [NaOH] = 0.05 M
  3. Use the pH formula: pH = 14 + log[OH⁻]
  4. Calculate log(0.05): log(0.05) ≈ -1.3010
  5. Add to 14: 14 + (-1.3010) ≈ 12.6990
  6. Round to two decimal places: pH ≈ 12.70

The pH of the 0.05 M NaOH solution is approximately 12.70, indicating a strongly alkaline solution.

Interpreting the Results

The pH of 12.70 for a 0.05 M NaOH solution indicates a strongly alkaline solution. Here's what this means:

  • The solution is highly basic and will react strongly with acids.
  • It will turn red litmus paper blue and will have a bitter taste.
  • The concentration of hydroxide ions is 0.05 M, meaning there are 0.05 moles of OH⁻ per liter of solution.

Comparing this to other common solutions:

Solution pH Characteristics
0.05 M NaOH 12.70 Strongly alkaline
0.01 M NaOH 13.00 Very strongly alkaline
0.1 M NaOH 12.00 Moderately alkaline

Frequently Asked Questions

Why is the pH of a 0.05 M NaOH solution approximately 12.70?

The pH is calculated using the formula pH = 14 + log[OH⁻]. For a 0.05 M NaOH solution, [OH⁻] = 0.05 M, so pH = 14 + log(0.05) ≈ 12.70. This indicates a strongly alkaline solution.

Can I use this calculator for other concentrations of NaOH?

Yes, the calculator can be used for any concentration of NaOH. Simply enter the molar concentration in the calculator to get the corresponding pH.

What is the difference between pH and pOH?

pH measures the concentration of hydrogen ions (H⁺), while pOH measures the concentration of hydroxide ions (OH⁻). The relationship between pH and pOH is given by pH + pOH = 14 at 25°C.