Required practical

Preparation of a pure, dry sample of a soluble salt from an insoluble oxide or carbonate

This required practical involves the preparation of a pure, dry sample of a soluble salt from an insoluble oxide or carbonate using a Bunsen burner to heat dilute acid and a water bath or electric heater to evaporate the solvent.

It is important in this practical to:

  • use appropriate heating devices safely
  • use appropriate apparatus and techniques, including a suitable choice of reactants
  • safely use equipment to purify or separate mixtures by filtration, evaporation and crystallisation
  • handle substances carefully, and mix them safely

The description below outlines one way to carry out the practical. Eye protection must be worn.

Aims

To prepare a pure, dry sample of a soluble salt from an insoluble oxide or carbonate.

Planning the practical

The plan needs to address these points:

  • which apparatus to use, and diagrams showing how it will be set up
  • which reagents to use
  • a consideration of hazards, risks and precautions

Apparatus

The apparatus required for each stage is:

  • mixing the solid and acid - beaker and stirring rod
  • filtering the mixture - conical flask, filter paper and filter funnel
  • heating the solution - water bath (beaker of water on a tripod and gauze, heated over a Bunsen burner) and evaporating basin
  • crystallisation - watch glass
Solid and solution are poured from a beaker into a filter funnel lined with funnel paper and dropping into a beaker.Filtering the mixtureA beaker of boiling water with a evaporating basin of solution is placed on a tripod and gauze above a blue flame bunsen burner.Heating the solution

Reagents

The acid and solid need to be chosen. Use hydrochloric acid to make a chloride, sulfuric acid to make a sulfate, and nitric acid to make a nitrate.

The solid must:

  • include the correct metal ions
  • react with the acid
  • be insoluble in water

Hazards, risks and precautions

Identify the hazards and suggest precautions needed to reduce the risk of harm. For example:

HazardPossible harmPrecaution
Hydrochloric acidConcentrated acid is corrosive and damages skin and clothesUse dilute hydrochloric acid
Bunsen burner and hot apparatusBurnsDo not touch hot apparatus
Bunsen burner and hot apparatusHair or clothing catching fireTie back long hair and tuck in ties or other loose clothing

This table does not include all possible hazards.

Carrying out the practical

Eye protection must be worn throughout.

  1. Add powdered insoluble reactant to acid in a beaker, one spatula at a time, stirring to mix. Continue adding powder until it is in excess (some unreacted powder is left over).
  2. Filter the mixture in the beaker to remove the excess powder. Collect the filtrate.
  3. Pour the filtrate into an evaporating basin. Place on a water bath, and heat until about half the water from the solution has been removed by evaporation. Stop heating when small crystals start to appear around the edge of the evaporating basin.
  4. Pour the remaining solution into a watch glass, and leave in a warm, dry place for crystallisation to occur.
  5. If necessary, dry the crystals by dabbing gently with filter paper.

Evaluating the practical

The evaluation should address these points:

  • Were good quality crystals obtained? If so, why?
  • What improvements could be made to the method?
  • Was the practical carried out safely? What improvements could be made?