How is pH measured?

pH is a measure of the hydrogen ion concentration [H⁺] in a solution, indicating its acidity or alkalinity. It can be measured using several methods:

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1. Using a pH Meter (Electronic Method)

• Principle: Measures the voltage difference between a pH-sensitive electrode and a reference electrode, which corresponds to the [H⁺] concentration.
• Procedure:
  1. Calibrate the pH meter with standard buffer solutions (e.g., pH 4, 7, 10).
  2. Immerse the electrode in the sample solution.
  3. Read the pH value directly from the meter.
• Advantages: Accurate and precise; widely used in labs.

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2. Using pH Indicators (Colorimetric Method)

• Principle: Certain dyes change color depending on the pH of the solution.
• Procedure:
  1. Add a few drops of a pH indicator (like methyl orange, phenolphthalein, or litmus) to the solution.
  2. Observe the color change.
  3. Compare with a color chart to estimate pH.
• Advantages: Simple, cheap, no instruments required.
• Limitations: Less precise; suitable for approximate values.

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3. Using pH Paper (Litmus Paper or Universal Indicator Paper)

• Principle: Similar to indicators, the paper contains dyes that change color depending on acidity or alkalinity.
• Procedure:
  1. Dip the pH paper into the solution.
  2. Compare the resulting color with the pH scale provided with the paper.
• Advantages: Quick and portable.
• Limitations: Less accurate than a pH meter.

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Summary:

• Acidic solution: pH < 7
• Neutral solution: pH = 7
• Basic solution: pH > 7

In short, pH is measured either electronically with a pH meter or chemically using indicators or pH paper, depending on the required accuracy.