Seperation Techniques Flashcards
(22 cards)
What are mixtures in chemistry?
Mixtures in chemistry are collections of separate things all mixed together.
How can mixtures be separated?
The parts of a mixture can be separated by physical methods such as filtration, crystallisation, simple distillation, fractional distillation, and chromatography.
What is a physical method of separation?
A physical method is one that doesn’t involve a chemical reaction, so it doesn’t form any new substances.
What is an example of a mixture?
Air is a mixture of gases, mainly nitrogen, oxygen, carbon dioxide, and argon.
What is crude oil composed of?
Crude oil is a mixture of different length hydrocarbon molecules.
How do the properties of a mixture compare to its components?
The properties of a mixture are just a combination of the properties of its separate parts.
What is paper chromatography used for?
Paper chromatography is used to separate different dyes in an ink.
What is the first step in paper chromatography?
Draw a line near the bottom of a sheet of filter paper using a pencil.
Why should you use a pencil for the line in chromatography?
Pencil marks are insoluble and won’t dissolve in the solvent.
What should you do after adding a spot of ink to the filter paper?
Place the sheet in a beaker of solvent, ensuring the ink isn’t touching the solvent.
What happens as the solvent moves up the paper?
The solvent carries the ink with it, and different dyes will move at different rates, forming separate spots.
What is a chromatogram?
A chromatogram is the pattern of spots formed by the different dyes after chromatography.
What should you do when the solvent nearly reaches the top of the paper?
Take the paper out of the beaker and leave it to dry.
What is the solvent front in chromatography?
The solvent front is the point the solvent has reached as it moves up the paper.
What is a practical application of chromatography?
Chromatography is used to test athletes’ urine samples for performance-enhancing drugs.
What is filtration used for?
Filtration separates insoluble solids from liquids.
It can be used in purification to separate solid impurities from a liquid reaction mixture.
What does ‘insoluble’ mean?
Insoluble means the solid can’t be dissolved in the liquid.
What are the two methods to separate soluble solids from solutions?
The two methods are evaporation and crystallisation.
Describe the evaporation process.
1) Pour the solution into an evaporating dish. 2) Slowly heat the solution until the solvent evaporates and crystals start to form. 3) Keep heating until only dry crystals remain.
You can use a water bath or an electric heater instead of a Bunsen burner.
What should you do if the salt decomposes when heated?
You should use crystallisation instead of evaporation.
Describe the crystallisation process.
1) Pour the solution into an evaporating dish and gently heat. 2) As some solvent evaporates, crystals will start to form. 3) Remove from heat when crystals form and let cool. 4) Filter the crystals and leave them to dry.
You could use a drying oven or a desiccator.
How can filtration and crystallisation be used to separate rock salt?
1) Grind the mixture to make salt crystals small. 2) Put the mixture in water and stir; salt dissolves, sand does not. 3) Filter the mixture to separate sand from salt solution. 4) Evaporate the water to obtain dry salt crystals.
Crystallisation can also be used to make larger crystals.
