3.4 Separation of Substances

Question 1

hand separation

Answer 1

where mechanical mixtures are separated by hand or by the use of a sieve or magnet

Question 2

filtration

Answer 2

where mechanical mixtures involving solids and liquids are passed through a filter to separate solids from liquids or larger chunks from smaller chunks

Question 3

residue

Answer 3

material that remains on the filter paper after the filtration method of separation is used

Question 4

filtrate

Answer 4

liquid which passes through the filter paper after the filtration method of separation is used

Question 5

evaporation

Answer 5

where the liquid in a solid in liquid solution (or liquid in liquid if they have very different BP) is evaporated or boiled away, leaving the solid behind

Question 6

distillation

Answer 6

where a liquid in liquid (or solid in liquid, less common) solution is heated in a distillation setup, the liquid with the lowest BP boils first, the vapour ascends to the distillation flask, passes a thermometer, enters the side-arm of the flask and contacts the cold inner surface of the condenser, where it cools back in liquid and drops out of the condenser

Question 7

distillate

Answer 7

the purified liquid that drops out of the condenser after the distillation method of separation is used

Question 8

when are re-distillations necessary

Answer 8

when the liquids present have boiling temperatures which are quite close to each other

Question 9

solvent extraction: solid from a mechanical mixture of solids

Answer 9

where a liquid is used to dissolve one or more of the solids present, but leaves others undissolved

Question 10

an ideal case of solid in solid solvent extraction is…

Answer 10

when there are only two solids present so that the desired solid either:

1. is left behind
2. dissolved and may be separated with evaporation later

Question 11

miscible

Answer 11

if two liquids are mutually soluble in each other in all proportions

Question 12

immiscible

Answer 12

if two liquids are insoluble in each other

Question 13

solvent extraction: dissolved liquid or solid from a liquid solution

Answer 13

where the added solvent is immiscible with the solvent already present and can dissolve the desired substances from the solution and leave the unwanted substance behind (or vice versa)

Question 14

When is a separatory funnel used?

Answer 14

When solvents form layers in solvent extraction.

Question 15

When using a separatory funnel, assume 80% if the desired substance leaves, if you repeat this process, how much will be left after three extractions?

Answer 15

0.20 x 0.20 x 0.20 = 0.008 = 0.8%

Question 16

recrystalization

Answer 16

where a solid in liquid solution is separated in a pure crystalline state –> a saturated solution of a desired solid is prepared in a suitable solvent (adding a solid to a solvent at room temperature until no more solid dissolves or adding just enough hot solvent to dissolve the solid), the solvent is then allowed to slowly evaporate or cool, and as it does some desired solid comes out of the solution as crystals (SORRY GUYS, IK THIS IS SUPER LONG)

Question 17

saturated solution

Answer 17

a solution that has dissolved all of the solid it can, all the solvent present is just enough to keep the solid dissolved

Question 18

true or false: the solvent used during the recrystallization method is allowed to evaporate completely

Answer 18

FALSE

Question 19

When is the recrystallization method most commonly used?

Answer 19

When the solid consists mostly of the desired material and small amounts of one or more impurities

Question 20

fractional crystallization

Answer 20

sometimes used to describe the process of purifying a substance by recrystallization

Question 21

gravity separation

Answer 21

where desired solids from a mechanical mixture are separated, based on their density

Question 22

centrifuge

Answer 22

equipment that whirls a test tube around at extremely high speeds forcing finely dispersed solids to the bottom of the test tube

Question 23

precipitate

Answer 23

solid formed in a liquid solution as a result of a chemical reaction

Question 24

paper and thin layer chromatography

Answer 24

where a drop of solid in liquid mixture is put a near one end of a chromatography sheet and allowed to dry, another liquid (the developing solvent) is allowed to absorb into the lower end of the chromatographic sheet containing the mixture and the liquid is absorbed up the sheet, a solvent front is seen as the liquid slowly moves upwards

Question 25

What do paper chromatography and thin layer chromatography use?

Answer 25

A sheet of absorbent paper and a thin layer of dried silica gel on a sheet of glass or plastic

Question 26

What do paper chromatography and thin layer chromatography use?

Answer 26

A sheet of absorbent paper and a thin layer of dried silica gel on a sheet of glass or plastic.

Question 27

During chromatography, why does one solid stop earlier and one later?

Answer 27

The solid that stops earlier has a greater tendency to stick to the sheet and less tendency to dissolve in the solvent. The solid that stops later has a greater tendency to dissolve in the solvent and a less tendency to stick to the paper

Question 28

column chromatography

Answer 28

where a tube is packed with stationary phase, the mobile phase is poured on top of the stationary phase, and finally a developing solvent is poured on top of the column –> the solvent spreads out and separates the components of the mixture

Question 29

stationary phase

Answer 29

a porous, absorbent solid such as powdered silica gel or resin beads

Question 30

mobile phase

Answer 30

the solution containing the mixture of dissolved solids

Question 31

When can chromatography be used on apparently colourless solids?

Answer 31

If the solids can glow when they are exposed to ultraviolet light