How to Do Titration Calculations

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A titration is a technique used to work out the concentration of an unknown solution based on its chemical reaction with a solution of known concentration. The process usually involves adding the known solution (the titrant) to a known quantity of the unknown solution (the analyte) until the reaction is complete. To calculate the concentration of the analyte, you measure the volume of titrant used.

  1. Prepare the Concentrations

  2. Place the analyte in an Erlenmeyer flask (a conical flat-bottomed laboratory flask with a narrow neck). Place the titrant in a burette (a graduated glass tube with a tap at one end).

  3. Mix the Concentrations

  4. Add the titrant to the analyte until the endpoint is reached. This is often indicated by a color change, for example by adding a few drop of phenolphthalein, a commonly used acid‑base indicator, which changes from pink in alkali to colorless in acid.

  5. Calculate the Molarity

  6. Use the titration formula. If the titrant and analyte have a 1:1 mole ratio, the formula is molarity (M) of the acid x volume (V) of the acid = molarity (M) of the base x volume (V) of the base. (Molarity is the concentration of a solution expressed as the number of moles of solute per litre of solution.)

    If the ratio is not 1:1, use a modified version of the formula. For example, if 35 ml of 1.25 M hydrochloric acid (HCI) is needed to titrate a 25 ml solution of sodium hydroxide (NaOH) to the equivalence point, you can work out the concentration of NaOH using the 1:1 ratio formula, because hydrochloric acid and sodium hydroxide have a 1:1 mole ratio (one mole of HCl reacts with one mole of NaOH).

    Multiply the molarity of the acid by the volume of the acid (1.25 x 35). Then take this answer (43.75) and divide it by the volume of the base (25). The answer is 1.75 M, which is the molarity of the base.

    Tips

    • A titration calculation is a simple formula used to work out the concentration (in moles) of one of the reactants in a titration using the concentration of the other reactant. Titrations are usually carried out on acid-alkali reactions, to determine what volumes of the acid and alkali are required to create a neutral solution. They may involve a strong acid with a strong base, a weak acid with a strong base, or a strong acid with a weak base.

References

About the Author

Claire is a writer and editor with 18 years' experience. She writes about science and health for a range of digital publications, including Reader's Digest, HealthCentral, Vice and Zocdoc.

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