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Chemistry > TOPIC 6 Organic Chemistry > Flashcards

TOPIC 6 Organic Chemistry Flashcards

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1
Q

A saturated hydrocarbon molecule contains four carbon atoms. How many hydrogen atoms does it have in a molecule?

A

10

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2
Q

Consider the compound with the formula C2F4

(a) Is it an organic compound? Explain your answer
(b) Is it saturated or unsaturated? Explain your answer

A

(a) yes because it contains carbon atoms

(b) unsaturated as it contains a C=C double bond

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3
Q

What is structural isomerism?

A

Same molecular formula, different structural formula

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4
Q

What is chain isomerism?

A

A type of structural isomerism when molecules have different carbon chains

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5
Q

What is position isomerism?

A

A type of structural isomerism when the same functional group is attached in different positions on the same carbon chain

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6
Q

What is stereoisomerism?

A

Same molecular formula, same structural formula but different arrangement

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7
Q

What is geometric isomerism?

A

A type of stereoisomerism when the C=C bond fixes the position of the atoms or groups attached at different positions

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8
Q

Why does cis-trans notation not work with all compounds?

A

Because there needs to be a double bond for it to occur

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9
Q

When naming E-Z isomers, what does priority mean?

A

The atom with the highest atomic number

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10
Q

What are the three types of fossil fuel?

A

Coal, crude oil and natural gas

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11
Q

Which organic compound are crude oil and natural gas mainly composed of?

A

Alkanes

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12
Q

What are the three main ways in which crude oil is converted into fuels?

A

Fractional distillation
Cracking
Reforming

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13
Q

How does fractional distillation work?

A

Crude oil is heated in a furnace and then passed into a column where it condenses based on each compounds boiling point

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14
Q

What type of compounds condense at the bottom of a fractioning column?

A

Large molecules, with longer chains and higher boiling temperatures

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15
Q

What type of compounds condense at the top of a fractioning column?

A

Small molecules, with shorter chains and lower boiling temperatures

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16
Q

What does cracking do?

A

Break long chain molecules into shorter chain molecules

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17
Q

Why is cracking used?

A

there is a surplus in longer chain molecules and they do not have many uses but there is a high demand for shorter chained molecules as they are better fuels and can be used to make other substances such as polymers

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18
Q

How is cracking carried out?

A

The hydrocarbons are passed through a heated catalyst, usually zeolite

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19
Q

What is reforming?

A

Converting straight-chains alkanes into branched and cyclic alkanes

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20
Q

Why is reforming done?

A

Because straight chain alkanes burn less effectively than branched and cyclic ones

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21
Q

How is reforming carried out

A

The straight chain alkanes is heated with a catalyst (usually platinum)

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22
Q

One molecule of the alkane C12H26 is cracked to form two molecules of ethene and one molecule of a different alkane. What is the molecular formula of the alkane formed?

A

C8H18

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23
Q

The products of a cracking reaction are two molecules of ethene and one molecule of pentane. What is the molecular formula of the alkane cracked?

A

C9H20

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24
Q

Why are alkanes burned? Give an example

A

To provide energy such as propane which is sold in containers at higher pressure for used as a fuel in homes and when camping

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25
Q

Why does incomplete combustion sometimes occur? (2)

A

Insufficient oxygen

Combustion is very rapid

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26
Q

When carbon is produced during complete combustion, how is it seen and what other products are formed?

A

Smoke in the air or spot on the burner

Carbon dioxide and water

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27
Q

Why is carbon monoxide deadly?

A

It is a toxic gas that prevents the transport of oxygen around the body

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28
Q

What else can sometimes occur in incomplete combustion and what happens when this occurs?

A

The hydrocarbon doesn’t burn at all and a small proportion of the hydrocarbons are released into the atmosphere unchanged ( known as unburned hydrocarbons , HC )

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29
Q

What else can be found in crude oil and why are they difficult to remove?

A

Atoms containing sulphur , cannot be removed by fractional distillation , cracking or reforming

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30
Q

What are the chemical reactions that occur with sulphur atoms during combustion? (2)

A

S + O2 —> SO2

2SO2 + O2 —> 2SO3

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31
Q

SO2 and SO3 are acidic oxides- what does this mean and what are the chemical reactions?

A

They dissolve in water in the atmosphere:
SO2 + H2O —> H2SO3 ( sulphurous acid )
SO3 + H2O —> H2SO4 ( sulphuric acid )

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32
Q

What do sulphurous acid and sulphuric acid contribute to and what is the effect of this?

A

Formation of acid rain - responsible for a lot of environmental damage , including damage to aquatic life in lakes and rivers , and damage to crops and forests

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33
Q

What are the equations for the combustion of alkanes containing nitrogen, what conditions are needed and what are the properties of some of the products? (3)

A

All occur at high temperatures
N2 + O2 —> 2NO
2NO + O2 —> 2NO2 —> acidic , can dissolve
2NO2 + H2O —> HNO2 + HNO3 —> both contribute to environmental damage

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34
Q

What metals do catalytic converters contain (3) and how are they made?

A

Platinum , palladium and rhodium

Spread thinly over a honeycomb mesh to increase the surface area

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35
Q

Which pollutants do 3-way catalytic converters remove?

A

Carbon Monoxide , unburned hydrocarbons and oxides of nitrogen

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36
Q

What are the 3 chemical reactions that occur in 3-way catalysts?

A

2CO + O2 —> 2CO2 ( oxidation of CO )
C8H18 + 12.5O2 —> 8CO2 + 9H2O ( oxidation of unburned hydrocarbons )
2NO + 2CO —> N2 + 2CO2

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37
Q

Which type of compounds are catalysts which are currently used not very good are getting rid of?

A

Sulphur compounds

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38
Q

What is the best way to prevent sulphur based pollution?

A

Remove the sulphur compounds before the fuel is burned

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39
Q

Summarise information about the products of combustion of alkanes, including names and whether complete or incomplete combustion was involved

A

Complete combustion: carbon dioxide and water

Incomplete combustion: carbon , carbon dioxide and water OR carbon monoxide , carbon dioxide and water

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40
Q

No carbon dioxide is formed when hydrogen is burned. Suggest why hydrogen is not a carbon neutral fuel.

A

Hydrogen does not occur naturally, it has to be manufactured. This uses energy, some of which comes from burning fossil fuels.

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41
Q

Summarise reasons why biofuel may not be carbon neutral.

A

The plants from which biofuels are obtained may need fertilising by pesticides produced from organic chemicals. The plants are then harvested, transported and processed using energy from fossil fuels.

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42
Q

What are the 3 mains concerns about the combustion of fossil fuels?

A

Pollution caused by combustion
The depletion of natural resources
Global warming and climate change

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43
Q

What is the purpose of biofuels?

A

Type of new fuel that is an alternative to fossil fuels

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44
Q

What are some examples of renewable resources? (5)

A 
Biofuels
Sunlight
Wind
Waves and tides
Geothermal energy
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45
Q

What are some examples of non-renewable resources? (3)

A

Coal
Oil
Natural gas

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46
Q

What is carbon neutrality in the example of wood?

A

If a tree is cut down and the wood is burned, then carbon dioxide is formed in combustion - if the amount formed is the same as the amount absorbed then the wood is carbon neutral as the amount of carbon dioxide in the atmosphere has not been altered by its combustion

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47
Q

Why are fossil fuels, such as those formed from trees, not carbon neutral?

A

The carbon dioxide was absorbed from the atmosphere millions of years ago when the amount in the atmosphere was much higher. Therefore, when fossil fuels are burned, the amount of carbon dioxide in the atmosphere increases

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48
Q

What is biodiesel?

A

Starting materials - present in vegetable oils such as those obtained from rapeseed and sunflowers
Proving a very effective alternative to ordinary diesel and can also be mixed with ordinary diesel

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49
Q

What are bioalcohols?

A

Most common is bioethanol
Refers to the ethanol produced in a different way involving bacterial rather than enzymes —> also possible to use a much wider range of plants and also plant waste
The upper limit to the amount of ethanol that can be obtained from a given amount of starting material is increasing and is much fighter than fermentation

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50
Q

Why are alkanes fairly unreactive?

A

They contain only carbon and hydrogen atoms and single bonds
The bonds are not very polar and so do not undergo reactions with substances that are considered to be very unreactive , such as acids and alkalis and reactive metals

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51
Q

What do mechanisms do?

A

Try to explain the actual changes that occur during a reaction, especially in the bonding between the atoms.

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52
Q

Under what conditions does the chlorination of methane occur?

A

High temperatures OR

Room temperature if the mixture is exposed to ultraviolet radiation

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53
Q

What is step 1 in the halogenation of an alkane?

A

Initiation
UV radiation breaks down the chlorine molecule into chlorine atoms
Each chlorine atom takes one electron from the shared pair
This kind of bond breaking is called homolytic fission

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54
Q

What is step 2 in the halogenation of an alkane

A

Propagation
The halogen radical collided with the alkane molecules and they react by removing a hydrogen atom.
The alkyl radical formed then reacts with the halogen molecules
Both equations involve one radical reacting with one radical and produce one radical and one molecule
The 2 steps considered together result in the conversion of an alkane into a halogenoalkane

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55
Q

What is step 3 in the reaction of a halogen with an alkane?

A

Termination reactions

When 2 radicals collide to form a molecule as the unpaired electrons are shared to form a covalent bond

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56
Q

What are further substitution reactions and why do they sometimes occur?

A

When the hydrogen atoms in the product are replaced one by one with the halogen
It is not easy to prevent them from occurring

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57
Q

The general formula for alkenes is CnH2n.

Why does cyclohexene not have this general formula?

A

It is a cyclic structure , so it has two fewer hydrogen atoms than the corresponding non-cyclic compound

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58
Q

Alkenes are not used as fuels because they are more valuable for other purposes, but they do burn very well. Write an equation for the complete combustion of propene.

A

C3H6 + 4.5O2 —> 3CO2 + 3H2O

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59
Q

What is the general formula of alkanes?

A

CnH2n+2

60
Q

What is the general formula of alkenes?

A

CnH2n

61
Q

When drawing structures of alkenes, what angle do you normally show the bond at?

A

120

62
Q

What is the general formula for cycloalkenes?

A

CnH2n-2

63
Q

Does the C=C bond makes alkenes more or less reactive?

A

More reactive

64
Q

What are sigma bonds?

A

Bonds that occur in all covalent bonds that involve the overlapping of orbitals.

65
Q

What are Pi bonds and when do they occur?

A

When there are 3 sigma bonds around each carbon atom in ethene, each carbon atom has one electron in a p-orbital that has not been used
The p-orbitals are parallel to each other and are not able to overlap in the same way as sigma bonds
When they do overlap, this results in the formation of two regions of negative charge above and below the sigma bond
This type of bonds is formed by the sideways overlap of orbitals
Each of these regions of negative charge contains one electron so together they make a second pair of electrons between the two carbon atoms

66
Q

Write equations for the reactions between but-2-ene and:

(a) hydrogen
(b) bromine
(c) hydrogen chloride

Using IUPAC rules, write the names of the products of these reactions.

A

C4H8 + H2 —> C4H10 Butane
C4H8 + Br2 —> C4H8Br2 2,3-dibromobutane
C4H8 + HCl —> C4H9Cl 2-chlorobutane

67
Q

Which is stronger: sigma bond or pi bond? Why?

A

Sigma bonds because electrons are more tightly held between the 2 carbon atoms than Pi bonds

68
Q

What occurs in most reactions involving alkenes?

A

A double bond becoming a single bond - the sigma bond remains unchanged but the Pi bond electrons are used to form new bonds with an attacking molecule

69
Q

What is the chemical test for the presence of a C=C bond?

A 
Adding bromine ( or bromine water )
Bromine is decolourised (brown/orange —> colourless)
70
Q

What is hydrogenation? What are the conditions needed to carry it out?

A

An addition reaction in which hydrogen is added to an alkene

Heat + Nickel catalyst

71
Q

How is margarine manufactured?

A

Naturally occurring vegetable oils are unsaturated but when they react with hydrogen some of the C=C become C-C
This process changes the properties of the vegetable oil and converts it into a solid : margarine

72
Q

What is halogenation? What are it’s products?

A

An addition reaction in which halogen is added to an alkene

Produces dihalogenoalkanes

73
Q

What is hydration? What conditions are needed? What does it produce?

A

An addition reaction in which water ( or H and OH molecules ) are added to an alkene
Hearing the alkene with steam and passing it over a catalyst of phosphoric acid
Produces an alcohol

74
Q

What happens when a alkene is reacted with a hydrogen halide?

A

An addition reaction which forms a halogenoalkane

75
Q

How is an alkene oxidised to a diol?

A

An oxidising agent ( potassium manganate (VII) ) is used in acidic conditions ( usually dilute sulphuric acid )
The potassium manganate (VII) provides an oxygen atom and the water in the solution provides another and 2 hydrogen atoms

76
Q

Name the types of reactions that occur when:

(a) alkanes react with halogens
(b) alkenes react with halogens

A

(a) radical substitution , homolytic fission

(b) electrophilic addition , heterolytic fission

77
Q

What is the name of the major product formed when but-1-ene reacts with hydrogen chloride?

A

2-chlorobutane

78
Q

Why does a hydrogen halide react with an alkene?

A

Alkenes have a Pi bond which means the molecule is electron rich around the C=C bond which makes it attractive to other species that are electron deficient , such a polar molecules like hydrogen halides. These are polar because the halide is more electronegative than the hydrogen.

79
Q

Which end of the hydrogen halide is attracted to the electrons in the Pi bond and why?

A

The slightly positive end ( hydrogen ) because it has a slightly positive charge

80
Q

What happens in step one of electrophilic addition?

A

The electrons in the Pi bond move to the positive end of the molecule and the electrons in the bond of the attacking molecule all move to the negative end. 2 ions are formed, one of which is a carbocation.

81
Q

What happens in step 2 of electrophilic addition?

A

The 2 oppositely charged ions attract each other and react to form a new covalent bond

82
Q

What happens in the electrophilic addition of halogens?

A

Similar to that of hydrogen halides except the attacking halide doesn’t have a polar bond.
However, as it approached the C=C bond , the electrons in the Pi bond repel the electrons in the bond between the halide atoms and induce the molecule to become polar.

83
Q

What happens in electrophilic substitution when both the alkene and attacking molecule are unsymmetrical?

A

A major and minor product are formed. Which is which depends of whether the carbocation is primary, secondary or tertiary. Tertiary is the most stable , the secondary followed by primary and so the most stable one will form the major product. This because the positive charge can be spread over more atoms.

84
Q

How are polymers made?

A

Using compounds with C=C bonds.
Described as addition reactions because the alkene molecules add together in vast numbers
Conditions are a combination of high pressure and high temperature

85
Q

How are polymers named?

A

‘Poly’ followed by the name of the monomer in brackets. The ending ‘ene’ is still used even though the polymer formed is saturated

86
Q

How are polymers drawn?

A

The repeat unit is shown in brackets (curved or square)
The letter n is shown as a subscript after the bracket
There are covalent bonds shown passing through the brackets

87
Q

Summarise the advantages of polymers over traditional materials. (3)

A

Manufactured on a large scale in a variety of shapes and sizes
Lighter in weight
They are unreactive ( don’t corrode or rot )

88
Q

Summarise the advantages (3) and main disadvantage of incineration as a method of disposing of polymer waste.

A

Very little solid waste
Saves landfill space
Can be used to produce heat energy for homes and factories or to generate electricity

Contains other elements and toxic pollutants which can cause air pollution as they are not very easy to remove

89
Q

What are the main solutions to polymer waste? (2)

A

Do not use them unnecessarily

Do not throw away polymer waster

90
Q

What are the 3 ways of putting polymer waste to good uses?

A

Recycling
Incineration
Chemical feedstock

91
Q

How is the recycling of polymer waste carried out?

A

Sorting
Processing ( chopping the waste into small pieces and washing it )
Using it to make new materials using methods such as melting, moulding and fibre production

92
Q

How is polymer waste used as a chemical feedstock?

A

A process , similar to cracking , used to break down the polymer waste into gasses (hydrogen and carbon monoxide)
Produces a feedstock that can be used in other chemical reactions

93
Q

What are the advantages (2) and disadvantages (2) of biodegradable polymers?

A

Break down unlike traditional plastics
Broken down in the environment

Made from plant material - land is needed
The hydrogen and carbon atoms can not be directly used

94
Q

What are halogenoalkanes?

A

A homologous series of compounds with the general formula CnH2n+1X

95
Q

What makes halogenoalkanes reactive?

A

They contain a halogen atom with an electronegativity higher than that of carbon , so the C-X bond is polar

96
Q

What happens to reactivity of halogenoalkanes as you go down group 7 and why does this happen?

A

They become less reactive as the polarity of the C-X bond decreased as the electronegativity of the halogen decreases

97
Q

What happens in a hydrolysis reaction?

A

A halogenoalkane is added to water
A water molecule contains polar bonds and so the d- oxygen atom is attracted to the d+ carbon atom

RX + H2O —> ROH + HX

98
Q

How do you compare the rates of hydrolysis reactions?

A

Add silver nitrate solution so the progress of the reaction can be followed
Use ethanol as a solvent
Control variables such as temperature and the concentration and quantity of halogenoalkanes
Time up to when the precipitate appears

99
Q

Which halogen reacts the fastest in a hydrolysis reaction and why?

A

Iodine because bond breaking requires energy and the weaker bonds break more easily than stronger bonds and the C-I bond is the weakest

100
Q

Why would you expect chlorine to react the quickest in a hydrolysis reaction and why is this not the case?

A

Because it is the halogenoalkane with the most polar bond and should be expected to be the fastest to be hydrolysed because the d+ charge on the carbon atom is greatest so the attacking nucleophile should be attracted more strongly , however , there is a more important factor

101
Q

What is the substitution reaction for making alcohols? What is the attacking nucleophile?

A

Heating a halogenoalkane with aqueous potassium hydroxide under reflux
Attacking nucleophile is the OH- ion

102
Q

What is the substitution reaction for making nitriles? What is the attacking nucleophile?

A

Heating a halogenoalkane with potassium cyanide dissolved in ethanol under reflux
The attacking nucleophile is the CN- ion

103
Q

What is the substitution reaction for making primary amides? What is the attacking nucleophile?

A

Heat a halogenoalkane with excess ammonia solution in a sealed tube
The attacking nucleophile is the NH3 molecule

104
Q

Draw and explain the mechanism of the reaction between bromoethane and aqueous potassium hydroxide.

A

Start with the donation of a lone pair of electrons from the oxygen of a hydroxide ion to the electron deficient carbon atom and the formation of a C-O bond
At the same time , the electrons in the C-Br bond move to the Br atom , resulting in the breaking of the C-Br bond —> heterolytic fission

105
Q

Draw and explain the mechanism for the reaction between chloroethane and ammonia

A

The first step involves the donation of a lone pair of electrons deficient from the nitrogen of the ammonia to the electron deficient carbon atom and the formation of a C-N bond
At the same time , the electrons in the C-Cl bond move to the Cl atom , resulting in the breaking of the C-Cl bond
The second step involves another ammonia molecule acting as a base and removing a hydrogen ion from the ion formed

106
Q

How are elimination reactions carried out?

A

Using a different solvent , ethanol instead of water , causes a different reaction to occur
When a halogenoalkane is heated with ethanolic potassium hydroxide , the OH- ion acts as a base and not as a nucleophile
The hydrogen that reacts with the OH- ion is the one attached to a carbon atom next to the C in the C-X bond

107
Q

What is the general formula of alcohols?

A

CnH2n+1OH

108
Q

What is the equation for the combustion of ethanol?

A

C2H5OH + 3O2 —> 2CO2 + 3H2O

109
Q

What is halogenation of alcohols?

A

Replacing the hydroxyl group in an alcohol molecule with a halogen atom

110
Q

How is chlorination of alcohols carried out? What are the inorganic products?

A

Carried out using phosphorus (V) chloride
The reaction is very vigorous at room temperature
Inorganic products : phosphorus oxychloride and hydrogen chloride

111
Q

How is the chlorination of tertiary alcohols carried out? What is the inorganic product formed?

A

The alcohol is mixed ( by shaking ) with concentrated HCl at room temperature
H2O is the other product

112
Q

How is the bromination of alcohols carried out? What are the equations? What are the inorganic products formed?

A

Using a mixture of postassium bromide and about 50% concentration sulphuric acid
The reaction mixture is warmed with alcohol

KBr + H2SO4 —> KHSO4 + HBr
2KBr + H2SO4 —> K2SO4 + 2HBr

Potassium hydrogensulphate
Potassium sulphate

113
Q

What is the equation for the bromination of butan-1-ol?

A

CH3CH2CH2CH2OH + HBr —> CH3CH2CH2CH2Br + H2O

114
Q

How is the iodination of alcohols carried out? What is the inorganic product formed?

A

Using a mixture of red phosphorus and iodine
The reaction mixture , including the alcohol , is heated under reflux
The inorganic reagents react first to form phosphorus (III) iodide:

2P + 3I2 —> 2PI3

Inorganic product : phosphonic acid

115
Q

What is the equation for the iodination of ethanol?

A

3C2H5OH + PI3 —> 3C2H5I + H3PO3

116
Q

How is the dehydration of alcohols to alkenes carried out?

A

Heating the alcohol with concentrated phosphoric acid

The OH group and a hydrogen atom from an adjacent carbon atom being removed and a C=C double bond formed in the carbon

117
Q

What is oxidation in terms of alcohols?

A

The loss of hydrogen from an alcohol molecule

118
Q

Which atoms are removed in the oxidation of alcohols?

A

The hydrogen of the OH grouoband a hydrogen atom from the carbon atom joined to the OH group

119
Q

Which classification(s) of alcohol can and can’t be oxidised and why?

A

Primary and secondary alcohols can be but tertiary alcohols can’t be because there isn’t another hydrogen atom attached to the carbon that the OH group is attached to

120
Q

What group does organic product of oxidation contain?

A

C=O , carbonyl group

121
Q

What are ketones and what is their simplified formula (written and drawn)?

A

Formed when a secondary alcohol is oxidised

RCOR

122
Q

What are aldehydes and what is their simplified formula (written and drawn)?

A

Formed when a primary alcohol is partially oxidised

RCHO

123
Q

What can sometimes happen when an aldehyde is formed during oxidation, why does this happen and how does it occur?

A

The aldehyde may be oxidised further to a carboxylic acid as aldehydes are more easily oxidised than alcohols
The process involves the gain of an oxygen atom which goes between the C and H of the CHO group

124
Q

What is a carboxylic acid and what is it’s simplified formula (written and drawn)?

A

Formed when a primary alcohol is fully oxidised

RCOOH

125
Q

What is the usual reagent for oxidation reactions and what colour change is seen when this agent is used?

A

A mixture of potassium dichromate (VI) and dilute sulphuric acid
Orange —> green

126
Q

What is the equation for the oxidation of propan-1-ol to propanal?

A

CH3CH2CH2OH + [O] —> CH3CH2CHO + H2O

127
Q

What is the equation for the oxidation of propanal to propanoic acid?

A

CH3CH2CHO + [O] —> CH3CH2COOH

128
Q

What is the equation for the oxidation of propan-2-ol to propanone?

A

CH3CH(OH)CH3 + [O] —> CH3COCH3 + H2O

129
Q

When the oxidation of an alcohol is intended to be complete , what could be formed and what apparatus would be needed? Include a labelled drawing of this apparatus.

A 
Ketone or carboxylic acid
Heating under reflux
Pear shaped flask containing reaction mixture 
Condenser vertical
Open top
130
Q

When the oxidation of an alcohol is intended to be incomplete , what could be formed and what apparatus would be used? Include a labelled diagram.

A

Aldehyde
Distillation with addition
Pear shaped flask with oxidising mixture
Alcohol above oxidising mixture in a separating funnel connected by a still head
Horizontal condenser with receiver adaptor at the end with receiver round bottom flask attached collecting the aldehyde

131
Q

Butan-1-ol can be dehydrated to form one organic product but can be oxidised to form 2 organic products. Give the names and structures of these 3 products.

A

Dehydration:

CH3CH2CHCH2 but-1-ene

Oxidation:

CH3CH2CH2CHO butanal

CH3CH2CH2COOH butanoic acid

132
Q

Pentan-2-ol can be dehydrated to form more than one organic product , but can only be oxidised to form one organic product. Give the names and structures of these products.

A

Dehydration:

CH3CH2CH2CHCH2 pent-1-ene

CH3CH2CHCHCH3 pent-2-ene

Oxidation:

CH3CH2CH2COCH3 pentan-2-one

133
Q

What might organic products be contaminated by (4)?

A

Unreacted starting materials
Other organic products
The inorganic reagents used or the inorganic products formed from them
Water

134
Q

Summarise the process of simple distillation and draw a labelled diagram of the apparatus.

A

Distillation of an impure liquid involves heating it in a flask connected to a condenser
The liquid with the lowest boiling point boils off first and passes into the condenser first so it can be collected separately

135
Q

What is the purpose of a thermometer during distillation?

A

To monitor the temperature of the vapour as it passes into the condenser.
If the temperature remains steady , this is an indication that one compound is distilling over
If, after a while, the temperature begins to rise, this indicates that a different compound is distilling over

136
Q

What is an advantage of simple distillation over fractional distillation?

A

It is quicker and easier to set up ; fractional distillation takes a long time to be carried out

137
Q

What is the advantage of using fractional distillation over simple distillation?

A

Fractional distillation provides better separation and is better for liquids with very similar boiling temperatures

138
Q

Summarise the process of fractional distillation and draw a diagram of the apparatus.

A

Uses the same apparatus as simple distillation but with a fractioning column between the heated flask and still head
The column is filled with glass beads or pieces of broken glass which acts as surfaces on which the vapour leaving the column can condense and then be evaporated again as more hot vapour passes up the column
Effectively the vapour undergos several repeated distillations as it passes up the column

139
Q

What is solvent extraction?

A

Using a solvent to remove the desired organic product from the other substances in the reaction mixture

140
Q

What properties does the solvent used in solvent extraction need to have?

A

Should be immiscible with the solvent

Must be much less soluble than the desired organic product

141
Q

Summarise the process of solvent extraction and draw a diagram of the apparatus used.

A

Place the reaction mixture into a separating funnel and then add the solvent - should form a separate layer
Place the stopper in and shake gently
Allow the contents to settle into 2 layers
Remove the stopper and open the tap to allow the lower layer to drain then pour the upper layer into a separate flask
The desired organic product is now mixed with the solvent so should be separated by simple or fractional distillation

142
Q

In solvent extraction , how should the solvent be added and why?

A

Should be added in small portions because this is more efficient

143
Q

How might water be an impurity in organic products and how is it removed?

A

Many organic products are prepared using inorganic reagents in aqueous solution
Removed using a drying agent

144
Q

What is an important feature of a drying agent and which are the most common?

A

Does not react with the organic liquid
Anhydrous metal salts eg. Calcium sulphate, magnesium sulphate and sodium sulphate
All form hydrated salts so when the come into contact with water they absorb it as water if crystallisation
Anhydrous calcium chloride can be used for some organic products although it does react with some and is soluble in alcohols

145
Q

Summarise the process of drying.

A

The drying agent is added to the organic liquid and the mixture is swirled for shaken and then left for a period of time
Before use, the drying agent is powdery but after absorbing water it looks more crystalline
If a bit more drying agent is added and it stays powdery this is an indication that the liquid is dry
The drying agent is removed either by decantation or filtration

146
Q

How do you test if a liquid is pure?

A

Measure it’s boiling temperature against that in data booklets - impurities raise the boiling temperature

Chemistry (6 decks)

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