seperating mixtures Flashcards
What is a mixtures?
A mixture is made up of two or more elements or compounds which are not chemically combined together
What is the composition like in a compound?
They have a fixed composition, which means that the ratio of the elements present is always the same in any particular compound
How can the elements in a compound be separated?
A chemical reaction is needed
What are the type of bonds present in a compound?
There are chemical bonds between atoms of the different elements in the compound
What is the composition like in a mixture?
There is no fixed compositions, and so the proportions vary depending on the amount of each substance mixed together
How can the elements or compounds in a mixture be separated?
These can be separated more easily, which can be done by physical means using the differences in properties of each substance in the mixture
What are the type of bonds present in a mixture?
There are no chemical bonds between atoms of the different substances in a mixture
What techniques are there available to separate various mixtures?
- filtration
- distillation
- crystallization
- chromotography
When is filtration used to separate a mixture?
To separate substances that are insoluble in a particular solvent from those that are soluble
How is filtration carried out?
- a conical flask or beaker is used to collect the filtrate
- a funnel, with filter paper inside it, is placed on top of the flask or beaker
- the substance to be separated is poured into the funnel
- the residue is left on top of the filter paper
How can pure sand be obtained from a mixture of sand, salt and water?
1) filtration would be used to separate the sand from the salt solution
2) then the sand would be washed with distilled water to remove any salt left in solution on it
3) finally it would be dried in a warm oven
When is crystallization used to separate a mixture?
To obtain a sample of pure salt from the sand / salt mixture, and after filtration has happened
How would the salt and water be separated?
The sodium chloride would need to be got from the solution in water through crystallization
How could a pure salt sample be collected from the salt solution?
- the water is evaporated from the sodium chloride solution by heating it in an evaporating dish on a water bath
- heating should stop when the solution is at the point of crystallization
- the rest of the water is then left to evaporate off the saturated solution at room temperature to get a good sample of crystals
Why might a water bath be used for crystallization rather than directing on a tripod and gauze?
The water bath is a gentler way of heating the substance
How would the salt and water be separated?
The sodium chloride would need to be got from the solution in water through crystallization
What is distillation used for?
To collect the solvent that was mixed with a soluble solid instead of just letting it evaporate off into the air
What happens in distillation?
- the solution is heated and boiled to evaporate the solvent
- the vapour given off is then cooled and condensed back into a liquid for collection
- the dissolved solids remain in the heated flask
Why might a flat bottomed crystallization dish or Petri dish be used for the final step?
To give a large surface area for the water to evaporate from
What is distillation used for?
To collect the solvent that was mixed with a soluble solid instead of just letting it evaporate off into the air
What happens in distillation?
- the solution is heated and boiled to evaporate the solvent
- the vapour given off is then cooled and condensed back into a liquid for collection
- the dissolved solids remain in the heated flask
What other mixtures can distillation separate?
Miscible liquids, such as ethanol and water
What are miscible liquids?
Liquids that dissolve in each other, and so they do not form separate layers as in immiscible liquids. The liquids also have different boiling points
How do the different boiling points of miscible liquids affect distillation?
These can be used to distill off and collect the liquid with the lowest boiling point first
Why is it difficult to get pure liquids from mixtures of liquids by simple distillation?
Because vapour is given off from the liquids before they actually reach their boiling point. This is especially the case when the liquids in the mixture have similar boiling points
How can the problems of simple distillation be overcome?
To aid separation, a fractioning column can be added to the apparatus
What is the fractioning column?
This is usually a tall glass column filled with glass beads, fitted vertically on top of the flask being heated
How does the fractioning column help the process of distillation?
The vapours must pass over and between the glass beads before they reach the condenser. Therefore the substance with the higher boiling point will condense more readily on the glass beads, and drop back down into the flask beneath
