Prepare a Soluble Salt II (Edexcel IGCSE Chemistry)

Spec point — describe an experiment to prepare a pure, dry sample of a soluble salt, starting from an acid and alkali

Prepare a soluble salt II

• It is also possible to prepare a sample of a dry salt starting from an acid and an alkali
• A titration can be used for this

Preparation of a soluble salt using a titration

Diagram showing the apparatus needed to prepare a salt by titration

Method

• Use a pipette to measure the alkali into a conical flask and add a few drops of indicator (phenolphthalein or methyl orange)

• Add the acid into the burette and note the starting volume

• Add the acid very slowly from the burette to the conical flask until the indicator changes to appropriate colour

• Note and record the final volume of acid in burette and calculate the volume of acid added

  • Final volume of acid - initial volume of acid when using a burette

• Add this same volume of acid into the same volume of alkali without the indicator

• Heat to partially evaporate, leaving a saturated solution

• Leave to crystallise decant excess solution and allow crystals to dry

Exam Hint When evaporating the solution some water is left behind to allow for water of crystallisation in some salts and also to prevent the salt from overheating and decomposing.