Separation and purification 2.0 Flashcards
Two substances are likely to be the same (on a chromatogram) if: (2)
they produce the same number of spots, and these match in colour
the spots travel the same distance up the paper (have the same Rf value)
what can Rf values be used to identify? why is this possible?
unknown chemicals if they can be compared to a range of reference substances.
-the Rf value is always the same for a particular substance.
equation for Rf value:
distance travelled by substance/ distance travelled by solvent
describe how the variation of Rf values from 0 to 1 reflects the substance’s attraction to the mobile and stationary phase:
0 = the substance is not attracted at all to the mobile phase 1 = the substance is not attracted at all to the stationary phase
what must happen to waste water and groundwater?
must be treated to make them potable, or safe to drink.
describe the different separation methods that are used to remove objects from water: (5)
- large objects are removed by screening using grids
- a coarse filter bed removes larger insoluble grit particles
- aluminium sulfate is added to clump smaller insoluble particles together, which then settle to the bottom in a sedimentation tank
- a fine filter bed removes very small insoluble particles
- chlorine gas is added to kill harmful microorganisms
what does seawater contain too much of? and how can this be resolved to produce pure water?
- dissolved salt
- simple distillation.
describe the process of simple distillation for seawater: (2)
- seawater is boiled and water vapour is led away and cooled.
- it is then condenses to form pure water, leaving the salt behind.
why is simple distillation for seawater impractical?
It is expensive since large amounts of energy are needed to heat the seawater
describe an advantage of simple distillation? (2)
useful in the laboratory for dissolving substances.
-since it does not contain any dissolved ions that might interfere with a chemical analysis.
