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How to Use an Old pH Meter for Titration

Titration is a technique used to determine the quantity of a substance based on its chemical reaction with another reagent (titrant). A standard solution of the titrant is slowly added using a burette to a flask with the solution of an unknown concentration. The reaction endpoint is characterized by a sharp change of the solution acidity (pH), and can be determined with a pH meter. A pH meter consists of glass electrodes and an analog or digital scale that displays a pH value. An old pH meter, which may be not calibrated or precise, still is useful for acid--base titration because it allows detection of the rapid pH change at the titration endpoint.

Things You'll Need

  • pH meter
  • Flask, 200-250 ml
  • Burette
  • Burette holder
  • Support stand
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Instructions

    • 1

      Fill in the burette to the zero ("0") mark with the standard solution of the titrant; e.g., 0.2 molar solution of sodium hydroxide.

    • 2

      Add a 10 ml aliquot of the solution with the unknown concentration of the compound (e.g., hydrochloric acid, HCl) to the flask.

    • 3

      Add approximately 100 ml of distilled water to the flask and swirl the flask for 2 to 3 seconds to mix the solution.

    • 4

      Place the glass electrode of the pH meter to the solution in the flask. Write down the initial pH of the solution.

    • 5

      Add 2 to 3 drops of the titrant solution from the burette to the flask.

    • 6

      Swirl the flask for 2 to 3 seconds to mix the solution. Record the pH value. Note: you should see a smooth and steady increase of the solution pH.

    • 7

      Repeat Steps 5 and 6 until you see a very rapid pH jump by 3 to 4 units. This is the titration endpoint.

    • 8

      Record the volume of the standard solution of sodium hydroxide used for titration.

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