Topic 2- Separation and purification of substances (Paper 1)
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What factors affect how far a compound moves in chromatography?
• How soluble they are up the solvent • How attracted they are to the paper
How do you calculate an Rf value?
Rf value = distance travelled by solute / distance travelled by solvent ink/disolvy stuff 😎
Method for carrying out a paper chromatography
• Draw a line near the bottom of a sheet of filter paper with pencil as it is insoluble (this is the baseline) • Spot the ink by placing dot of it on the line • Put the sheet upright in a beaker of slovent • Make sure that the ink isn’t touching solvent initially as you don’t want it to be washed away. • Place a watch glass on top of the beaker to stop the solvent evapourating away. • Solvent will start to move up the paper. When the chemicals in the ink dissolve in the solvent they will move up the paper too. • The different dyes in the ink will move up the paper at different rates. Any insoluble inks will stay at the baseline. • When the solvent front has nearly reached the top of the paper, remove the paper from the beaker and draw a line with a pencil along the solvent front before leaving it to dry.
How can you identify a pure substance from chromatography?
A pure substance will not be separated by chromatography and instead it will remain in one spot
Describe the process of water purification
• Filtration- a wire mesh screens out large twigs, gravel and sand beds filter out any solids • Sedimentation- Iron sulphate or aluminium sulphate is added to make fine particles clump together and settle at the bottom • Chlorination- chorine gas is bubbled through to kill harmful bacteria and other microbes
How would sea water be made potable?
Distilling it- but requires a lot of energy
Why might you not use ionised water in chemistry?
Mineral ions could interfere with results
Method to crystalise soluble solids
• Place evapourating dish on top of tripod and gauze mat. • Pour solution into evapourating dish and gently heat. • Once water has evapourated or crystals start to form remove dish from heat and leave to cool. • Dissolved compound should start to form crystals as it becomes insoluble in the cold highly concentrated solution • Filter the crystals out of the solution using a drying oven or desiccator.
What are sources of water?
• Surface water • Ground water from aquifers • Waste water
In what ways can a solid be separated from a liquid?
Not dissolved → filtration Dissolved → evapouration
In what ways can a liquid be separated from a liquid?
Immiscible liquids (haven’t mixed) → separating funnel Miscible liquids → fractional distillation
In what ways can you separate two solids?
Dissolving → one substance is soluble but not the other Chromatography → dissolved solids