Chapter 4: Separation Techniques

Question 1

pure substance

Answer 1

• it is not mixed with any other substance
• fixed melting and boiling point

Question 2

solutions

Answer 2

well-mixed (homogeneous)

Question 3

suspensions

Answer 3

not well-mixed (heterogeneous)

Question 4

filtration

Answer 4

separates insoluble particles from a liquid in a suspension

Question 5

what is the solid left behind on the filter paper (filtration)

Answer 5

residue

Question 6

what is the liquid / solution that passes through the filter paper (filtration)

Answer 6

filtrate

Question 7

why can’t the insoluble solid particles pass through the pores of the filter paper (filtration)

Answer 7

they are too large

Question 8

evaporation to dryness (liquid-solid)

Answer 8

to obtain a soluble solid from a solution by heating the solution until all the solvent has boiled off

Question 9

what substances cannot be obtained through evaporation to dryness

Answer 9

substances that decompose upon heating (eg. sugar)

Question 10

solute and solvent

Answer 10

solute (solid) is dissolved in the solvent (liquid) to form a solution

Question 11

simple distillation (liquid-liquid)

Answer 11

separates 2 liquids of different boiling points from a solution
involves boiling and condensation

Question 12

process of simple distillation

Answer 12

1. solution is heated by a bunsen burner (luminous flame)
2. liquid with the lower boiling point will gain heat and turn into vapour
3. the vapour condenses in the condenser into its liquid state
4. the liquid will be collected as distillate

Question 13

why is the bulb of the thermometer placed beside the side arm of the distillation flask?

Answer 13

to ensure the thermometer measures the boiling point of the substance that is being distilled

Question 14

purpose of boiling chips

Answer 14

to smoothen boiling process (reduces the bubbles on the surface of the solution)

Question 15

why does water from the surroundings enter the condenser? (water in) (distillation)

Answer 15

to ensure the entire condenser is filled with cold water
condenses the vapour

Question 16

applications of distillation

Answer 16

production of distilled water
desalination
production of alcoholic drinks
production of perfumes
food flavourings

Question 17

paper chromatography

Answer 17

• separates 2 or more components that dissolves in the solvent
• used to identify components in mixtures

Question 18

a more soluble component travels a ? distance (paper chromatography)
a. further
b. shorter

Answer 18

a. further

Question 19

the larger the Rf value, the ? soluble the component of the solvent (paper chromatography)
a. more
b. less

Answer 19

a. more

Question 20

formula for Rf value (paper chromatography)

Answer 20

distance travelled by substance / distance travelled by solvent

*just remember smaller value / larger value
*round to 3 sf

Question 21

impure substance

Answer 21

does not have fixed melting and boiling points

Question 22

effects of impurities on melting point of a substance

Answer 22

-melts over a range of temperature
-can melt below melting point
-*more impurities=lower melting point

Question 23

effects on impurities on the boiling point of a substance

Answer 23

-boils over a range of temperature
-boils above boiling point
-*more impurities=higher boiling point

Question 24

crystallisation (solid-solid)

Answer 24

separates soluble solute that decomposes on heating from its solution

Question 25

as the mass of dissolved solute increases, the temperature of the remaining solute ? (crystallisation) a. increases b. decreases

Answer 25

a. increases

Question 26

define solubility

Answer 26

the ability to dissolve in a solvent

Question 27

process of crystallisation to obtain salt

Answer 27

1. dissolve the impure copper(ii) sulfate crystals in water 2. filter and collect the filtrate which is copper(ii) sulfate solution 3. heat the solution until saturated 4. filter to collect the crystals

Question 28

saturated solution

Answer 28

it contains all solute components and can dissolve at a certain temperature

Question 29

unsaturated solution

Answer 29

any solution that dissolves more solute at a higher temperature

Question 30

relationship between saturated solution and unsaturated solution

Answer 30

when a saturated solution is heated to a higher temperature, it becomes unsaturated. when it is cooled, it becomes unsaturated

Question 31

fractional distillation

Answer 31

is used to separate misciblr liquids with different but close boiling points

Question 32

why are there glass beads in the fractionated column (fractional distillation)

Answer 32

provides a large surface area for vapour to condense on

Question 33

what happens to the vapour in the fractionating column (fractional distillation)

Answer 33

vapour with higher boiling point condenses along the fractionating column and re-enters the round-bottomed flask