4.2.5 Titrations

Titrations are a common laboratory technique used to determine the precise volumes of acid and alkali solutions needed to react completely with each other. This technique involves the use of a suitable indicator, which changes colour when the reaction reaches the equivalence point. The equivalence point is the point at which the reactants have completely reacted with each other in stoichiometric proportions.

Conducting Titrations

When conducting a titration, it is important to use strong acids and strong alkalis to ensure complete and rapid reaction. Common examples of strong acids used in titrations include sulfuric acid (H₂SO₄), hydrochloric acid (HCl), and nitric acid (HNO₃).

Here is a step-by-step procedure for conducting a titration:

1. Prepare a known volume of the acid solution in a conical flask.
2. Add a few drops of a suitable indicator to the acid solution. The indicator will change colour when the reaction reaches its endpoint.
3. Fill a burette with the alkali solution of known concentration.
4. Slowly add the alkali solution from the burette into the conical flask, while continuously swirling the flask.
5. As the alkali solution is added, the indicator will change colour. When the colour change is permanent, this indicates that the reaction has reached its endpoint.
6. Record the volume of the alkali solution required to reach the endpoint. This volume is known as the titre.
7. Repeat the titration process until consistent results are obtained.

Calculating Chemical Quantities in Titrations

Calculating the chemical quantities involved in titrations includes calculating concentrations in mol/dm³ and in g/dm³.

Calculating the concentration (in mol/dm³) of the alkali solution:

1. Use the known volume and concentration of the alkali solution to calculate the number of moles of the alkali solution used in the titration.
2. Divide the number of moles by the volume (in dm³) of the alkali solution used to obtain the concentration in mol/dm³.

Calculating the chemical quantities in the titration:

1. Use the balanced chemical equation for the reaction between the acid and alkali to determine the stoichiometry of the reaction.
2. From the stoichiometry, calculate the number of moles of the acid and alkali that reacted.
3. Use the concentration of the acid solution and the volume of the acid solution used in the titration to calculate the number of moles of the acid used.
4. Use the stoichiometry to determine the number of moles of the alkali that reacted.
5. Calculate the mass of the acid or alkali used using the molar mass of the substance.

Conclusion

By accurately carrying out titrations and performing these calculations, you can determine the reacting volumes and chemical quantities involved in acid-base reactions, providing valuable insights into the concentrations and stoichiometry of the reactants.