Section 2 - States of matter and mixtures - Purification, chromatography and water treatment Flashcards
What is a pure substance?
A substance completely made up of a single element or compound
What is simple distillation used for?
Separating out a liquid from a solution (e.g. pure water from sea water)
What is fractional distillation used for?
Separating a mixture of liquids
What is filtration used for?
Separating an insoluble solid form a liquid
What is crystallisation used for?
Separating a soluble solid from a solution
4 methods of purification?
Simple distillation, fractional distillation, filtration, and crystallisation
What is chromatography used for?
Separating a mixture of soluble substances and identifying them
Two phases in chromatography and what are they?
Mobile phase - where molecules can move. This is always a liquid or a gas
Stationary phase - where the molecules can’t move. This can be solid or really thick liquid
In chromatography, why do the components in a mixture separate out as mobile phase moves over stationary phase and end up in different places?
Each of the chemicals in mixture spend different amounts of time dissolved in mobile phase and stuck to stationary phase
In paper chromatography, what is the stationary phase and the mobile phase?
Stationary phase - piece of filter paper (chromatogram)
Mobile phase - Solvent
Why should the baseline on a chromatogram in paper chromatography be drawn in pencil and not pen?
Pencil marks are insoluble and won’t move with solvent as ink might
Two things the amount of time the molecules spends in each phase depend on in paper chromatography?
How soluble they are in solvent and how attracted they are to stationary phase
What is the Rf value? Formula for Rf value?
The ratio between distance travelled by dissolved substance (solute) and distance travelled by solvent
Rf = distance travelled by solute ÷ distance travelled by solvent
What is potable water?
Water that is fit to drink
3 types of water sources?
Surface, ground and waste water
3 processes in which water is purified in water treatment plants and what happens in each process?
Filtration - wire mesh screens out large twigs etc. then gravel and sand bends filter out any other solid bits
Sedimentation - iron- or aluminium- sulfate added to water to make fine particles clump together and settle at bottom
Chlorination - chlorine gas bubbled through to kill harmful bacteria and other microbes
Con of distillation sea water to get potable water?
Distillation needs loads of energy so really expensive
What is deionised water?
Water that has had the ions present in normal tap water removed
