Methods Flashcards
Determine the mass of water present in hydrated crystals
Weigh and record mass of crucible
Add around 25g of hydrated compound, weigh and record mass of crucible and hydrated compound
Place the crucible in a pipe clay triangle and heat to remove the water of crystallisation
Allow the crucible to cool, then weigh and record mass
Repeat the heating, cooling a and reweighing until two masses are the same (heat to constant mass)
Determine the mass of water present in hydrated crystals other
Think about safety!
The crucible is very hot after heating so must be cooled between weighings. Use tongs.
Why do we heat to constant mass?
To ensure that all the waster of crystallisation is driven off
Investigate the reactions of acids including the temperature which occur
Carefully measure 25 cm3 of hydrochloric and place it in the polystyrene cup
Take the initial temperature of the hydrochloric acid and record it
Then measure 25 cm3 of sodium hydroxide solution into the measuring cylinder
Add the sodium hydroxide solution to the acid, stir with the thermometer, measure and record the highest temperature reached during the reaction.
Repeat the experiment using ethanoic acid in place of hydrochloric acid.
Preparation of soluble salt from acid and alkali
Carried out by titration of an acid against an alkali
Pipette 25.0cm3 alkali into a conical flask.
Phenolphthalein indicator is added and goes pink
Run acid from the burette until the indicator goes colourless.
Remove the indicator by adding activated charcoal, heating and filtering.
(If an ammonium salt is being produced you must use methyl orange which will change from yellow to red during the titration)
Evaporate half the water by heating to produce a saturated solution.
Cool to crystallise
Dry in a low temperature oven, in a dessicator or between two sheets of filter paper
Preparation of soluble salt from acid and base/metal carbonate
Add excess solid to acid in a beaker, heat and stir.
Filter to remove insoluble solid (residue) and pour into evaporating dish.
Evaporate half the water by heating to produce a saturated solution.
Cool to crystallise
Dry in a low temperature oven, in a desiccator or between two sheets of filter paper.
Chromatography
Using a PENCIL, draw a line 2 cm from the bottom of the chromatography paper.
Put a small dot of the ink sample in the centre of the bottom line.
Pour a suitable solvent (water) into the beaker to a depth of no more than 1 cm.
Place the chromatography in the beaker. Make sure the pencil line is above the water surface and the sides of the paper do not touch the beaker wall.
Wait for the solvent (water) to run three quarters of the way up, then remove the paper and use a pencil to mark the solvent front. (The furthest point reached by the solvent)
Allow the chromatogram to dry.
The different components (dyes) present in the black ink can then be identified
Common chromatography question
Why does THE PENCIL line need to be above the solvent line?
The sample would dissolve in the solvent.
Don’t say RUN!
Flame test
Dip nichrome wire into conc. HCl and hold in hot Bunsen flame until clean
Dip wire into conc. HCl and into sample
Hold at edge of blue Bunsen flame
Observe & record colour
Describe how you would test for chloride ions in a sample
Dissolve a sample spatula of sample in deionised water in a test tube
Add nitric acid followed by silver nitrate solution
White precipitate observed
