Required practical - preparation of soluble salt
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 Able to dissolve in solvent. For example, sugar is soluble in water because it dissolves to form sugar solution. The substance formed when the hydrogen ion in an acid is replaced by a metal ion. from an Unable to dissolve in a particular solvent. For example, sand is insoluble in water. oxide or Substance containing carbonate ions. Most carbonates are insoluble (such as calcium carbonate) but sodium carbonate and ammonium carbonate are soluble in water. using a Bunsen burner to heat dilute Substance producing more hydrogen ions than hydroxide ions when dissolved in water. and a water bath or electric heater to evaporate the The liquid in which the solute dissolves to form a solution..
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 Method used to separate an insoluble solid from a liquid using a physical barrier such as paper., The process in which a liquid changes state and turns into a gas. and The process of producing crystals from a solution by evaporating the solvent.
- 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
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:
| Hazard | Possible harm | Precaution |
| Hydrochloric acid | Concentrated acid is corrosive and damages skin and clothes | Use dilute hydrochloric acid |
| Bunsen burner and hot apparatus | Burns | Do not touch hot apparatus |
| Bunsen burner and hot apparatus | Hair or clothing catching fire | Tie back long hair and tuck in ties or other loose clothing |
| Hazard | Hydrochloric acid |
|---|---|
| Possible harm | Concentrated acid is corrosive and damages skin and clothes |
| Precaution | Use dilute hydrochloric acid |
| Hazard | Bunsen burner and hot apparatus |
|---|---|
| Possible harm | Burns |
| Precaution | Do not touch hot apparatus |
| Hazard | Bunsen burner and hot apparatus |
|---|---|
| Possible harm | Hair or clothing catching fire |
| Precaution | Tie 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.
- Add powdered insoluble reactant to acid in a beaker, one spatula at a time, stirring to mix. Continue adding powder until it is in In chemistry, a substance is in excess if there is more than enough of it to react with another reactant. (some unreacted powder is left over).
- Filter the mixture in the beaker to remove the excess powder. Collect the filtrate.
- 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.
- Pour the remaining solution into a watch glass, and leave in a warm, dry place for crystallisation to occur.
- If necessary, dry the A solid containing particles (atoms, molecules or ions) joined together to form a regular arrangement or repeating pattern. 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?