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Calculate The Poh and Ph of The Following Aqueous Solutions

Reviewed by Calculator Editorial Team

This guide explains how to calculate pH and pOH values for aqueous solutions using our interactive calculator. You'll learn the formulas, understand the relationship between pH and pOH, and see practical examples of how these values are used in chemistry.

Introduction

The pH scale is a measure of how acidic or basic a solution is. It ranges from 0 to 14, where:

  • pH 0-6 is acidic
  • pH 7 is neutral (pure water)
  • pH 8-14 is basic

The pOH value is related to pH through the equation pH + pOH = 14. This relationship is fundamental to understanding aqueous solutions.

pH and pOH Formulas

pH Formula

pH = -log[H+]

Where [H+] is the hydrogen ion concentration in moles per liter (mol/L).

pOH Formula

pOH = -log[OH-]

Where [OH-] is the hydroxide ion concentration in moles per liter (mol/L).

Remember that pH and pOH are logarithmic scales, so small changes in concentration can result in large changes in pH or pOH values.

How to Calculate pH and pOH

To calculate pH and pOH:

  1. Determine the hydrogen ion concentration [H+] in moles per liter (mol/L)
  2. Calculate pH using the formula pH = -log[H+]
  3. Calculate pOH using the relationship pOH = 14 - pH

For basic solutions, you can first find the hydroxide ion concentration [OH-] and then calculate pOH before finding pH.

Worked Examples

Example 1: Acidic Solution

Given a solution with [H+] = 1 × 10-3 mol/L:

  1. pH = -log(1 × 10-3) = 3
  2. pOH = 14 - 3 = 11

This is an acidic solution with pH 3 and pOH 11.

Example 2: Basic Solution

Given a solution with [OH-] = 1 × 10-5 mol/L:

  1. pOH = -log(1 × 10-5) = 5
  2. pH = 14 - 5 = 9

This is a basic solution with pH 9 and pOH 5.

Interpreting Results

The pH scale provides valuable information about solution properties:

  • pH values below 7 indicate acidic solutions
  • pH 7 indicates a neutral solution (like pure water)
  • pH values above 7 indicate basic solutions

The pOH value complements pH by showing the concentration of hydroxide ions, which is particularly important in basic solutions.

FAQ

What is the difference between pH and pOH?
pH measures the concentration of hydrogen ions (H+) and ranges from 0 to 14. pOH measures the concentration of hydroxide ions (OH-) and is related by the equation pH + pOH = 14.
How do I calculate pH from pOH?
You can calculate pH from pOH using the equation pH = 14 - pOH. This is useful when you know the hydroxide ion concentration but not the hydrogen ion concentration.
What does a pH of 7 mean?
A pH of 7 indicates a neutral solution, like pure water. At this pH, the concentration of hydrogen ions equals the concentration of hydroxide ions.