CC2 Separating substances Flashcards
What is chromatography?
A process to separate the constituents of a mixture
In paper chromatography, what is the stationary phase and what is the mobile phase
Paper is stationary, solvent (usually water or ethanol) is mobile
How can chromatography show the difference between pure and impure substances?
Pure ones will not separate into a number of spots
How is the Rf value calculated?
distance moved by spot/distance moved by solvent
What does a substance’s Rf value depend on?
How soluble it is in the solvent
In chromatography, why must the substances be placed on a pencil line?
Pencil will not dissolve in the solvent
In chromatography why must the solvent height be lower than the pencil line?
So that the substances do not dissolve into the solvent off the paper
How is the melting point of a pure substance different from that of an impure substance?
Pure substance has one specific melting point. Impure substance has a melting range.
What is simple distillation used to separate?
A single liquid from a mixture
What is fractional distillation used to separate?
Multiple liquids of different boiling points
What is filtration used to separate?
An insoluble solid from a liquid
What is crystallisation?
Forming crystals of a soluble solid from a solution.
What is potable water?
Drinking water
How can sea water be made potable?
By distillation
What are the stages used to make water potable.
Sedimentation, filtration and chlorination
What is a pure substance?
A substance made of one type of atom or molecule only.
How would you separate water from salt water?
Simple distillation
How would you separate salt from salt water?
Crystallisation
Why must analysis be done with pure water?
Because dissolved salts in non pure water would give false positive results.
How is the melting point of a mixture different from a pure substance?
A pure substance has a single melting temperature, a mixture has a range of melting points.
