大象传媒

Acids and basesTitrations

The pH scale measures the acidity or alkalinity of a solution. A pH less than 7 is acidic. Alkalis dissolve in water to give a pH greater than 7. A pH equal to 7 indicates a neutral solution.

Part of ChemistryChemical changes and structures

Titrations

A titration experiment can be carried out to accurately measure the volume of substances that react in chemical reactions.

This technique is commonly used in neutralisation reactions and can also be used to calculate an unknown concentration (of either the acid or alkali).

When titrating, it is essential to measure things as accurately as possible.

The experiment is carried out by following these steps:

  1. If the sample is a solid, it is weighed using an accurate balance, and then dissolved to make up a known volume of solution (usually 100 cm3).
  2. A pipette is used to measure accurately a volume of this solution - for example, 10 cm3. A safety pipette filler is used to draw solution into the pipette. This is emptied into a conical flask.
  3. A few drops of an indicator may be added to the conical flask. This will show a change of colour when the titration is complete.
  4. A second chemical is placed in a burette. This other solution is of a chemical that will react with the sample in the conical flask. Often the solution in the burette is an acid of a precise, known concentration.
  5. The solution from the burette is run into the conical flask. The solution is added one drop at a time, with swirling to mix the solutions as the end-point is approached. Eventually, a colour change shows that the correct amount has been added to react completely with the sample in the conical flask.
  6. The volume of solution added from the burette is noted. The titration results can then be used to calculate the concentration of the sample in the conical flask.
Titration apparatus: a burette, conical flask, pipette and safety pipette filler.
Figure caption,
Titration apparatus: a burette, conical flask, safety pipette filler and pipette.

Calculate the concentration of an acid or alkali using the process of titration

Related links