topic 2- separating mixtures Flashcards
How can we tell if a substance is pure?
- pure substances have a horizontal line at the melting and boiling points
- pure substances have 1 melting point not a range
define an ‘element’
a substance that only consists of atoms with the same atomic number (number of protons in their nucleus)
define a ‘compound’
a substance that consists of atoms of two or more different elements chemically joined together
pure substances contain…
only one element or compund
define ‘mixtures’
substances containing different elements and/or compounds. They are impure substances. The components of a mixture are NOT chemically joined together.
How can we tell if a substance is impure?
-it has a range of temperatures instead of a single temperature
What does simple distillation separate?
A solvent from a solution
How does simple distillation work?
-simple distillation works because the solute in the solution has a much higher boiling point than the solvent
-when the solution is heated:
>the solvent boils
>solvent vapour passes into the condenser
>the vapour is cooled and condensed back to the liquid state
What does fractional distillation separate?
-a liquid from a mixture of miscible liquids (liquids that mix completely with each other)
How does fractional distillation work?
It works because the liquids in the mixture have different boiling points
-when the mixture is heated:
>the mixture boils
>hot vapour rises up the fractionating column
>vapour condenses when it hits the cool surface of the column and drips back
>the fraction with the lowest boiling point reaches the top of the column first
>it’s vapour passes into the condenser
What does filtration separate?
an insoluble substance from a liquid or a solution
when would you use filtration?
-to purify a liquid or a solution by removing solid impurities from it
»_space; i.e. sand from sea water
-to separate the solid you want from the liquid it is mixed in with
»_space; i.e. to separate crystals from a solution after crystallisation
How does filtration work?
Filtration works because the filter paper has tiny pores. These are
- large enough to let water molecules and dissolved substances through
- small enough to stop insoluble solid particles going through
What does crystallisation produce?
-solid crystals from a solution
Method of crystallisation:
- the solution is heated to remove enough solvent to produce a saturated solution (one that cannot hold any more solute)
- the saturated solution is allowed to cool
- crystals form in the solution
- the crystals are separated from the liquid and dried.
