Topic 2 - Seperating Mixtures Flashcards
What does it mean if a substance is ‘pure’ ?
It’s made up of only one element or compound
What is a mixture made up of?
Two or more different substances, that have not been chemically bonded
What’s the difference in melting points between pure substances and mixtures?
Pure substances have a sharp melting point, whereas mixtures melt over a range of temperatures
What is filtration used to separate?
An insoluble solid from a liquid.
Why does filtration work?
The filter paper has small holes in it, that allow small molecules through, but not larger particles.
Give an example of a mixture that could be separated using filtration
Sand and water
What equipment would you need to carry out a practical of filtration?
- filter paper
- filter funnel
- beaker
Describe crystallisation
Used to produce solid crystals from a solution. When the solution is warmed, some of the solvent evaporates, which leaves behind a more concentrated solution.
What equipment would you need to carry out a practical of crystallisation?
- heat (Bunsen burner)
- evaporating basin
What is simple distillation used to separate?
A solvent from a solution
Give an example of a mixture that simple distillation could be used to separate
Separating water from a salt solution
Why does simple distillation work?
The dissolved solute has a much higher boiling point than the solvent.
Describe a simple distillation practical, trying to gain pure water from salty sea water.
1) Heat the salty sea water
2) The water will boil and turn into water vapour
3) Water Vapour will cool and condense in the condenser and drip into a beaker
4) You will now have pure water in the beaker, and the salt will have stayed behind
What is fractional distillation used to separate?
A mixture of liquids
Give an example of a mixture that could be separated using fractional distillation
A mixture of ethanol and water
Why does fractional distillation work?
The different liquids have different boiling points
Give a rough description of how fractional distillation works
1) The mixture is heated
2) The substance with the lowest boiling point will evaporate, cool, and condense first
3) The substance with the next highest boiling point will then go through the same process
What is paper chromatography used to separate?
Mixtures of soluble substances
Give an example of a mixture that could be separated using paper chromatography
Ink from a pen
What are the two different phases of chromatography?
The stationary phase, and the mobile phase
What is the stationary phase in paper chromatography?
The paper
What is the mobile phase in paper chromatography?
The solvent
How do you calculate retention factor?
Rf = distance travelled by substance / distance travelled by solvent
What would an Rf value of 0 mean?
The substance is insoluble in the solvent, and has not moved from the start line
What would an Rf value of 1 mean?
The substance has moved as far as the solvent front, and is strongly attracted to the mobile phase
Why does paper chromatography work?
The different substances in the mixture are attracted to the two phases in different proportions, meaning they move at different rates through the paper
How many spots would a pure substance have in a chromatogram?
One
How many spots would an impure substance have on a chromatogram?
Two or more
