METHODS OF PURIFICATION & ANALYSIS

Question 1

when can FILTRATION be used?

Answer 1

when separating a mixture of liquid ( or solution ) and an insoluble solid. insoluble solid collected as residue while the liquid collected is filtrate.

Question 2

when can EVAPORATION be used?

Answer 2

used ONLY when substance/solute does not decompose upon heating
used to evaporate solvent from a solution to obtain the dissolved substance

Question 3

when can CRYSTALLISATION be used?

Answer 3

USEFUL for substances that decompose during heating!
carried out by heating a solution until it is saturated, SATURATED solution is left to cool and crystallise.

Question 4

when can SIMPLE distillation be used?

Answer 4

• when LIQUIDS/ SOLUTION have a large difference in boiling point
  used to separate liquids in a mixture

Question 5

when can FRACTIONAL distillation be used?

Answer 5

when mixture with two or more liquids have relatively close boiling point, used for purification
- vapour produced is a mixture of these substance, fractionating columns aids in separating the vapour into individual components which allows for collection of pure substances.

Question 6

when can paper chromatography be used?

Answer 6

separation of small quantities of mixture-> based on difference in solubility of its components in a particular solvent
* Identity of a component in a mixture can be deduced by comparing its spot with other spots produced by known substance-> ONLY if SOLVENT used is the same and distance travelled is the same.

Question 7

when can PURITY OF SUBSTANCE be used?

Answer 7

pure substances has a fixed boiling and melting point!
when impurities added, resultant mixture has a lower boiling point and freezing point + a higher boiling point as compared to pure subs.-> mixture also melts and boils over a range of temperature.
PURE SUBSTANCE- melt & boil over a range of temperatures
contains IMPURITIES- melts & boils over a range of temperature.

Question 8

STEPS TO CARRY OUT PAPER CHROMATOGRAPHY:

Answer 8

1) place a drop of ink on the start line drawn on the chromatography paper.
2) Similarly, place a drop of ink of the other few dyes on the start line of the chromatography paper.
3) place the paper in a beaker containing distilled water.
4) when solvent (distilled water) has reached the top of the chromatography paper, remove the chromatogram and let it dry
5) compare the spots formed on the chromatography paper-> if same distance with known substance = same substance

Question 9

define MISCIBILITY/ miscible

Answer 9

refers to how completely two or more liquids dissolve in eachother