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chemistry > Separating Mixtures > Flashcards

Separating Mixtures Flashcards

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1
Q

how do you identify a pure substance

A

by measuring its melting/boiling point because a pure substance has a specific, sharp melting/boiling point

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2
Q

what happens to the melting point of a solid if an impurity is present

A

the melting point is lowered

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3
Q

what happens to the boiling point of a liquid if a dissolved impurity is present

A

it increases the boiling point

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4
Q

what are the differences between a pure substance and a mixture

A

a pure substance is made up of a single element or compound but a mixture has two or more substances

a pure substances’ compound cannot be changed, but a mixtures can

a pure substance has a specific, sharp melting/boiling point but a mixture melts/boils over a range of temperatures

a compound cannot be separated into its elements using physical processes

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5
Q

why are flat sections seen on a cooling curve when a gas is condensing to liquid or a liquid is freezing to a solid

A

energy is given out when bonds are formed between the particles which prevents the continuation of cooling

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6
Q

what is a solution

A

a mixture of a solid substance dissolved in a liquid

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7
Q

what is a solvent

A

a liquid in which a substance dissolves in to form a solutin

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8
Q

what is a solute

A

a solid that dissolves in the solvent

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9
Q

what solvents are used to dissolves substances that are insoluble in water

A

white spirit, ethanol and propanone

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10
Q

what does magnetism do

A

separates magnetic materials from non-magnetic materials

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11
Q

what does crystallisation do

A

it separates a soluble solid from its solution

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12
Q

what does filtration do

A

it separates an insoluble solid from a liquid

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13
Q

what does simple distillation do

A

separates the solvent from its solution

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14
Q

what does fractional distillation do

A

separates liquids with different boiling points

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15
Q

what does chromatography do

A

it separates a mixture of different colours

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16
Q

explain the process of filtration

A

a filter funnel is lined with filter paper

the mixture is poured through the filter paper

the filter paper only allows liquids to pass through

the insoluble solid is left in the filter paper and the liquid is collected in the beaker below

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17
Q

what is the solid which remains in the filter paper

A

residue

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18
Q

what is the liquid that passes through the filter paper

A

filtrate

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19
Q

what are the hazards in filtration

A

you could slip and fall if some water was spilt on the floor

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20
Q

how do you avoid slipping on water split on the floor during filtration

A

mop up spillages immediately to reduce the risk of slipping

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21
Q

explain the process of crystallisation

A

heat the solution slowly using a gentle blue flame until most of the water evaporates

leave the solution in a warm place to cool and crystallise

the remaining solvent will evaporate slowly and crystals will form

dry the crystals between filter papers

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22
Q

how do you get large crystals in crystallisation

A

heat the solution slowly using a gentle blue flame

do not evaporate all of the water

leave the solution to cool at room temperature so crystals form

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23
Q

what are the hazards in crystallisation

A

if the solution is heated until too dry, the hot liquid/crystals could spit out from the evaporating basin causing burns

the apparatus will get too hot and could cause a burn if touched

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24
Q

how to avoid hot crystals spitting out in crystallisation

A

use a gentle blue flame and stop heating before the solution is dry.

Wear safety glasses

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25
Q

how to avoid being burned by hot apparatus in crystallisation

A

use a pair of tongs to hold hot apparatus

wear heat resistant gloves

26
Q

how do you make a solute dissolve more quickly in a solvent

A

grind up the solid / crush the solid with a pestle and mortar

dissolve the solid in a warm solvent

stir the mixture with a glass rod

27
Q

why are anti bumping granules added to the mixture in distillation

A

they are added to the flask so that the liquid boils smoothly

28
Q

why does the solute not evaporate

A

the boiling point is very high

29
Q

explain the process of distillation

A

the salt solution is heated in a round bottom flask

water boils and evaporates to form water vapour

the hot vapour rises from the flask and enters the condenser

as it passes through the condenser, the vapour is cooled and condensed. It changes from a gas to a liquid and the liquid drips into a beaker

30
Q

why should the cold water enter the condenser from the bottom and leave from the top

A

this keeps the condenser full of water

31
Q

why is the flaks heated gently during distillation

A

to stop the solution boiling over into the condenser

32
Q

how do you avoid hazards from using a bunsen burner flame in distillation

A

avoid naked flames as ethanol is flammable

use an electric heater to heat the flask

tie long hair and tuck in tie to avoid it catching fire

33
Q

how to avoid hazards from the liquid boiling too rapidly in distillation

A

add some anti-bumping granules to the flask

using an electric heater

34
Q

what is fractional distillation used for in industry

A

to separate the different fractions in crude oil

to separate the gases in liquid air

35
Q

explain the process of fractional distillation

A

a fractionating column containing glass beads is put on top of the flask. The fractionating column is hottest at the bottom and coldest at the top.

the mixture is heated, so the vapour rises

the liquids will have different boiling points so will evaporate at different temperatures

ethanol will leave the column first as it has a lower boiling point and water will leave second as it has a higher boiling point

36
Q

what is paper chromatography used for

A

to separate a mixture of different colours

distinguish between pure and impure substances

identify substances by calculating their rF values

37
Q

what is the stationary phase

A

the chromatography paper

38
Q

what is the mobile phase

A

the solvent e.g. water, ethanol etc….

39
Q

explain the process of chromatography

A

Draw a pencil line near the bottom of the chromatography paper

place small spots of the ink on the pencil line and allow them to dry

label the inks with a pencil

place the paper in a beaker of water so that the water level is below the pencil line

remove the paper when the water is near the top of the paper, and use a pencil to draw a line where he water has reached

dry the paper and examine the chromatogram

40
Q

how do you know if a substance is insoluble from a chromatogram

A

it did not move from its original position

41
Q

why should the base line not be draw in ink and only pencil

A

because the ink will move up the paper and confuse the results whereas pencil does not dissolve in the solvent

42
Q

what do you use if the substance is insoluble in water for chromatogrpahy

A

ethanol or propanone

43
Q

Rf =

A

distance travelled by the substance / distance travelled from the solvent

44
Q

what variables should be kept the same in chromatography

A

the same type of paper, the same solvent and the same temperature

45
Q

what are the hazards in chromatography

A

there could be a fire when organic solvents like ethanol are used

you could slip and fall if some water was spilt on the floor

46
Q

how to avoid fires when using organic solvents in chromatography

A

avoid naked flames

place a lid on the beaker/container to prevent the solvent from evaporating

47
Q

how to identify colourless substances in a mixture

A

Draw a pencil line near the bottom of the chromatography paper

place small spots of the ink on the pencil line and allow them to dry

label the inks with a pencil

place the paper in a beaker of water so that the water level is below the pencil line

remove the paper when the water is near the top of the water, and use a pencil to draw a line where he water has reached

dry the paper

spray the paper with a locating agent such as ninhydrin and warm the paper in an oven for 10mins

the amino acids will appear as purple spots

make a pencil dot at the top of each spot

measure the distance from the base line to each amino acid

measure the distance from the base line to the solvent front

calculate the Rf value for each amino acid

identify the amino acids by comparing Rf values obtained with Rf values of known amino acids

48
Q

what are the industrial uses of water

A

manufacture of ethanol

manufacture of sulfuric acid

manufacture of hydrogen/ammonia

in power stations

49
Q

why is distillation not suitable for producing drinking water

A

it uses large amounts of energy so is not suitable

50
Q

where do we get water in our homes from

A

rivers, lakes, aquifers or ground water

51
Q

how do you know if water is safe for drinking

A

it should contain no microbes and only low levels of dissolved substances

52
Q

what are the main stages in treating water to remove impurities make it safe to drink

A

screening
sedimentation
filtration
chlorination

53
Q

what is screening

A

the water from the river is pumped in and a sieve traps and removes any large objects such as leaves or twigs

54
Q

what is sedimentation

A

a coagulant is added to the water which makes small insoluble particles stick togehter

55
Q

what is filtration

A

the water is passed through a bed of sand and gravel to filter out insoluble solids. The sand and gravel traps the insoluble solids and the water drains through

56
Q

what is chlorination

A

small amounts of chlorine added to kill bacteria

57
Q

why may water that looks colourless and clean not be safe to drink

A

the water may contain microbes and some dissolved substances

58
Q

what water is used in chemical analysis

A

distilled water

59
Q

why is tap water not used in chemical analysis

A

it contains small amounts of dissolved salts for example nitrates

60
Q

what could happen if tap water was used in chemical analysis

A

the dissolved salts may react to form precipitates which will lead to incorrect conclusions and the salts will be detected by the machines leading to incorrect results

chemistry (21 decks)

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