Volumetric Analysis

Volumetric Analysis is the procedure of mixing a standard solution of known volume with a solution of known volume of unknown concentration. Volumetric analysis is done usually through titration and the purpose of this process is to ultimately find the unknown concentration of the solution. Usually, titration between solutions that will result in an acid-base reaction will be conducted and the titre is recorded once the end point has been reached.

The equivalence point is the point during a titration when all the solutions have been mixed together in their respective mole ratios as given by its overall balanced stoichiometric equation.
The end point is the point where the indicator/solution changes colour. Ideally, the end point and equivalence point should be the same however conditions such as temperature and insufficient stirring of solutions may lead to a lack of colour change even when solutions have been added in their mole ratios.
A standard solution is a solution with an accurately known concentration.

Primary standard are substances of high purity that their mole can be measured accurately from their mass. Some examples of primary standards include zinc powder, sodium carbonate and benzoic acid. Traits that define a primary standard include:

  • High Purity
  • Known formula
  • Easy to store (does not react with the atmosphere) – an example of a substance that easily reacts with the atmosphere is iron. Iron over time reacts with air moisture and oxygen and creates iron oxide/rust.

Simple Titrations

The process of mixing solutions in their specific mole ratios derived from the stoichiometric equation. Involves the use of common laboratory equipment such as conical flasks/beakers for holding solutions as well as burettes and pipettes for moving a specific amount of solution into different containers. For titrations, indicators are also used to help identify the end point of the reaction (when the indicator changes colour).

Titrations are usually repeated a minimum of 3 times and the average titre is used for calculations

Back Titrations

Back titrations are used for weak acids and bases that do not produce sharp colour change from simple titration and are unable to give an accurate end point/titre.

If the substance to be analysed is a weak acid, back titration will involve reacting it with excess strong base. All the weak acid will react in stoichiometric proportions and the unused excess base is titrated with a standard solution to find the amount of base that was used and unused.

See Also