methods of purifying and separating substances

Question 1

what is a mixture

Answer 1

a mixture consists of 2 or more elements or compounds not chemically combined together

Question 2

what happens to the chemical properties of substances in a mixture

Answer 2

chemical properties of each substance remain unchanged

Question 3

what is a pure substance

Answer 3

a single element or compound, not mixed with any other substance

Question 4

what is a pure substance in everyday language

Answer 4

a substance that has had nothing to it, so it is unadulterated and in its natural state, eg. pure milk

Question 5

what are the melting and boiling points like of a mixture

Answer 5

mixtures melt over a range of temperatures due to them consisting of 2 or more elements or compounds

Question 6

how are pure substances distinguished from mixtures

Answer 6

pure substances melt and boil at specific/exact temperatures so melting and boiling points data can be used to distinguish pure substances from mixtures

Question 7

what is simple distillation used for

Answer 7

simple distillation is used to separate a pure liquid from a mixture of liquids

Question 8

how does simple distillation work

Answer 8

simple distillation works when the liquids have different boiling points

Question 9

what is the sequence of events in distillation

Answer 9

heating ➡ evaporating ➡ cooling ➡ condensing

Question 10

what is simple distillation often used for

Answer 10

simple distillation is often used to separate ethanol from water

Question 11

how does fractional distillation work

Answer 11

the oil is heated in the fractioning volume and the oil evaporates and condenses at a number of different temperatures

Question 12

what are fractions from fractional distillation used for

Answer 12

the reactions can be processed to produce fuels and feedstock for the petrochemical industry

Question 13

what is a precipitate

Answer 13

an insoluble salt

Question 14

how does filtration work

Answer 14

to separate the salt/precipitate from the salt solution, you must filter the solution leaving behind the precipitate on the filter paper

Question 15

crystallisation

Answer 15

the process of separating a soluble salt from a solution

Question 16

what is the process of crystallisation

Answer 16

warm a solution in an open container, allowing the solvent to evaporate, leaving a saturated solution. allow it to cool. the solid will come out of the solution and crystals will start to grow, these can then be collected and allowed to dry.

Question 17

what is chromatography used for

Answer 17

chromatography is used to separate mixtures and die information to help identify substances

Question 18

what does chromatography involve

Answer 18

chromatography invoices a stationary phase and a mobile phase

Question 19

what does separation depend on in chromatography

Answer 19

separation depends on the distribution of substances between the phases

Question 20

what is the Rf value

Answer 20

distance moved by substance/distance moved by solvent (/ represents a dividing sign)

Question 21

what can chromatography graphs determine

Answer 21

compound in a mixture may separate into different spots depending on the solvent but pure compound will produce a single spot in all solvents.

Question 22

how to describe and appropriate experiment technique to separate a mixture

Answer 22

you need to which type of substance you have in the mixture and so which technique is the most appropriate

Question 23

pure substances

Answer 23

should only have one spot on a chromatogram

Question 24

impure substances/mixtures

Answer 24

will show up with more than one spot on a chromatogram

Question 25

potable water

Answer 25

it is suitable for drinking so must have low levels of microbes and low levels of contaminating substances. it is not the same as pure water but is still safe

Question 26

sedimentation

Answer 26

large insoluble particles will sink to the bottom of the water

Question 27

filtration

Answer 27

water is filtered through beds of sand which removes insoluble particles

Question 28

chlorination

Answer 28

chlorine gas is put through water to kill microbes

Question 29

steps to making waste and ground water potable

Answer 29

sedimentation ➡ filtration ➡ chlorination

Question 30

steps to making sea water potable using distillation

Answer 30

filter the water ➡ boil it ➡ water vapour is cooled and condensed

Question 31

water used in analysis

Answer 31

must be pure because any dissolved salts could react with the substances you are analysing, leaving you with a false result