Indicators are used to determine whether a solution is acidic or alkaline. Acids react with metals, bases and carbonates to produce salts. Neutralisation is the reaction between an acid and a base.
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 solublesalt 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
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
Filtering the mixtureHeating 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:
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
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 excess (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 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?