C1 More Separation Techniques (page 101) Flashcards
Apart from Chromatography, what other separating methods are there?
Filtration and Chystallisation are methods of separating mixtures too.
Why is filtration and Crystallisation methods used to separate mixtures?
they are used all the time by chemists to separate solids from liquids
What is Filtration?
it seperates Insoluable solids from liquids
When can you use the technique Filtration?
it can be used if your product is an insoluable solid that needs to be separated from a liquid reaction mixture
It can be used in purification as well. eg; solid impurities in the reaction mixture can be separated out using filtration
(insoluable means the solid cant be dissolved in the liquid)
If a solid can be dissolved, it is described as being what?
soluble.
What are the two methods you can use to separate a soluble salt from a solution?
Evaporation and Crystallisation
What is the Method of Evaporation?
1) Pour the solution into an evaporating dish
2) slowly heat the solution. The solvant will evaporate and the solution will get more concentrated. Eventually, crystals will start to form
3) keep heating the evaporating dish until all you have left are dry crystals
Evaporation is a really quick way of separating a soluable salt from a solution, but you can only use it if the salt doesn’t decompose (break down) when its heated. Otherwise, you’ll have to use crystallisation.
What is the method of Crystallisation?
1) Pour the solution into an evaporating dish, and gently heat the solution. Some of the solvent will evaporate and the solution will get more concentrated.
2) Once some of the solvent has evaporated, or when you see crystals start to form, (the point of crystallisation), remove the dish from the heat and leave the solution to cool.
3) The salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution.
4) Filter the crystals out of the solution, and leave them in a warm place to dry. You could also use a drying oven or a desiccator - (a glass container or other apparatus holding a drying agent for removing moisture from specimens ).
What can Filtration and Crystallisation be used to separate?
Rock Salt
What is Rock Salt a mixture of?
Salt and Sand (they spread it on the roads in winter)
Why can you separate the mixture of Salt and Sand (Rock salt)
They are both compounds - but salt dissolves in water and sand doesn’t.
The vital difference in their physical properties gives a great way to separate them.
What is the Method to separate Rock Salt?
1) Grind the mixture to make sure the salt crystals are small, so it will dissolve easily.
2) Put the mixture in water and stir. The Salt will dissolve, but the sand won’t (you can heat the mixture to help dissolve the salt).
3) Filter the mixture. the grains of sand won’t fit through the tiny holes in the filter paper, so they collect on the paper instead. The salt passes through the filter paper as it’s part of the solution.
4) Evaporate the water from the salt so that it forms dry crystals. (you could also use crystalisation here if you wanted to make nice big crystals)
A student needs to produce pure crystals of copper sulfate from an aqueous solution of copper sulfate. Describe how the student could use crystallisation for this process?
Pour the copper sulfate solution into an evaporating dish and slowly heat the solution until crystals start to form or some of the solvent has evaporated.
Leave the dish to cool until crystals form
Filter and then dry the crystals using a desiccator/drying oven
