Methods Of Purification

Question 1

Rf :

Answer 1

in chromatography, the distance moved by a particular substance from the baseline divided by the distance moved by the solvent front from the base line

Question 2

Locating agent

Answer 2

A substance that reacts with colourless spots on a chromatogram to make them visible as coloured spots

Question 3

Rf =

Answer 3

Distance of solvent front from baseline

Question 4

Simple distillation

Answer 4

A method of separating a volatile from a non-volatile substance by evaporation and condensation

Question 5

Volatile

Answer 5

Easily changed to a vapour. Volatile substances have low boiling points

Question 6

Crystallisation

Answer 6

1) heat the solution in an evaporating basin to concentrate it
2) evaporate the solvent until the crystallisation point (a drop of the solution forms crystals when placed on a cold tile)
3) leave the saturated solution to form crystals
4) filter off the crystals then dry them between filter papers

Question 7

Fractional distillation

Answer 7

Used to separate miscible liquids with different boiling points. It is used to separate petroleum fractions and to purify alcohol from a mixture of water and alcohol
There is a higher temp gradient in the column: higher at the bottom lower at the top
The more volatile components in the mixture (lower boiling points) move faster up the column
The less volatile components in the mixture ( higher boiling points) do not move as fast
The components of the mixture reach the condenser in turn, the most volatile first. They change from vapour to liquid in the condenser and the fractions containing particular components of the mixture and collected at one time.

Question 8

characteristics of a pure substance

Answer 8

sharp melting point

Question 9

characteristics of an impure substance

Answer 9

the solid melts over a temp range and it is lower

Question 10

impure- solid dissolved in liquid

Answer 10

liquid boils over a temperature range and at a higher temp than the pure liquid

Question 11

impure mixture of two liquids

Answer 11

the mixture starts boiling at the boiling point of the liquids and rises to the boiling point of the other liquid

Question 12

what is a locating agent

Answer 12

a substance that reacts with colourless spots on a chromotogram to make them visible as coloured spots.

Question 13

what are liquids that do not mix

Answer 13

immisicible e.g benzene and water

Question 14

what is simple distillation

Answer 14

a method of separating a volatile from a non-volatile substance by evaporation and condensation

Question 15

what is volatile

Answer 15

easily changed to vapour. volatile substances have low boiling points

Question 16

non volatile substances

Answer 16

are ones that do not vaporise rapidly and will most likely be solids at room temp

Question 17

why does food and medicine can’t be impure

Answer 17

could lead to undesirable side effects. it also helps ensure an accurate dose in each tablet or capsule

Question 18

what does the prescense of an impurity incur

Answer 18

usually lowers the melting point so therefore raises the boiling point

Question 19

ductile meaning

Answer 19

can be drawn into wires by a pulling force

Question 20

malleable meaning

Answer 20

can be beaten into different shapes

Question 21

lustrous meaning

Answer 21

shiny like a mirror