Salt by Acid-Alkali Titration

Specification Point 3.18:

• Describe how to carry out an acid-alkali titration, using a burette, pipette and a suitable indicator, to prepare a pure, dry salt.

Aim: 

• To investigate the preparation of a pure, dry salt by titration

Diagram showing the apparatus needed to prepare a salt by titration

Materials:

• Hydrochloric acid, sodium hydroxide solution, goggles and lab coat
• Suitable indicator (methyl orange or phenolphthalein), teat pipette
• Conical flask, burette, stand, volumetric pipette

Method:

• Use the pipette to measure the alkali into a conical flask and add a few drops of indicator.
• Add the acid into the burette and note the starting volume.
• Add the acid very slowly to the conical flask until the indicator changes colour.
• Note and record the final volume of acid in burette and calculate the volume of acid added.
• Repeat the procedure with the same volume of acid and alkali but without the indicator.
• Heat gently to partially evaporate the water, leaving a saturated solution.
• Leave in a dry place so the remaining water evaporates, allowing crystallisation to occur.
• This may take a few days depending on ambient conditions.

Analysis of results:

• After a few days record the appearance of the NaCl crystals to include a diagram and/or photograph.
• In particular comment on their colour and shape.

Conclusion:

• The titration method is used when the salt product is soluble, hence there is no need to filter any insoluble materials.
• The indicator is used to identity the amount of acid needed for neutralisation and is not used in successive titrations to avoid contamination of the product.
• Evaporation of the water leaves the desired pure salt.