Organic Chemistry
Structures
1
What do I need to know?
1. Translate between molecular, structural and ball
and stick representations of simple organic
molecules
2. Describe how the functional group affects the
property of an organic compound and
understand that alkanes are unreactive towards
aqueous reagents because C—C and C—H bonds
are unreactive;
3. Write balanced chemical reactions including for
burning hydrocarbons including state symbols
2
Representations of organic molecules
• There are a number of different ways to
represent organic molecules.
• Ball and stick – this is just like molymods
3
Representations of organic molecules
• Structural formula – this is where we show
the covalent bonds between atoms as a line
• Semi-structural (molecular) – this is where we
write out the formula but do not include
bonds; these are implied eg CH3CH2OH
4
• Molecular formula – this simply counts the numbers
of each sort of atom present in the molecule, but
tells you nothing about the way they are joined
together.
• Eg C2H6O
• This is the least helpful type of formula as it could be
one of two (or more) different chemicals
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Example question
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Rules of organic molecules
Generally speaking
Carbon must make four bonds
Nitrogen must make three bonds
Oxygen must make two bonds
Hydrogen must make one bond
A double bond counts as two bonds eg C=C or C=O.
A triple bond counts as three bonds.
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AfL - Quiz
1.
2.
3.
4.
5.
Draw the structural formula for butanol
Write the molecular formula for butanol
Draw the structural formula for hexane
Write the molecular formula for hexane
Write the molecular formula for an alkane with
25 carbon atoms.
6. How many bonds does oxygen make in
methanol?
7. Give an example of a use for ethanol
8. Give an example of a use for methanol
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1.
2.
3.
4.
5.
6.
7.
Butanol
C4H10O
Hexane
C6H14
C25H52
2
Fuel/feedstock for synthesis/solvent/used in
perfume
8. Solvent, antifreeze, feedstock for adhesives
and plastics
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Understanding reactivity
• Alkanes are unreactive towards aqueous
reagents because C-C and C-H bonds are
unreactive.
• What about organic molecules that have
different bonds?
• We call families of different types of bonded
atoms FUNCTIONAL GROUPS
• An example is the –OH group or alcohol
group.
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Different functional groups
Name
Functional group
Properties
Alkane
C-H
Relatively unreactive,
burns in air due to
hydrocarbon chain
Alkene
C=C
Used as a feedstock to
make polymers
Alcohol
-OH
Good solvent, volatile,
burns in air due to
hydrocarbon chain
Carboxylic acid
-COOH
Weak acid such as vinegar
Ester
RCOOR’
Have distinctive smells
such as fruits
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Alkanes and combustion
• Because of the hydrocarbon chain alkanes
burn readily releasing large amounts of
energy.
• Alkanes are therefore used as fuels.
• When they burn completely they make carbon
dioxide and water.
eg octane (found in petrol)
C8H18 +12 ½ O2 8CO2 + 9H2O
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Example question
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Example question
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Balanced chemical equations
Write the balanced chemical equation for
burning ethanol in air as a fuel and burning
pentane as a fuel (include state symbols).
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Answers
Ethanol
2C2H5OH(l) + 6O2(g)  4CO2(g) + 6H2O(l)
Pentane
C5H12(l)+ 8O2(g)  5CO2(g) + 6H2O (l)
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Example questions
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Mark scheme
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Alcohols and the Manufacture of
Ethanol
C7.1 and C7.5
22
What do I need to know?
1. The characteristic properties of alcohols are
due to the presence of an –OH functional group
2. Know a range of methods for synthesising
ethanol and limitations of fermentation
reactions
3. Be able to explain why bioethanol is
important for sustainability
23
Functional groups - reminder
• Look back at your table of functional groups.
• Write a short paragraph to explain why
different organic chemicals have different
properties in terms of functional groups.
• Use examples such as “carboxylic acids are
acidic because they have a –COOH group”.
24
Can you recognise the functional
group?
• Circle which of these are alcohols?
25
Answer
• Alcohols have an –OH group
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Properties and uses of alcohols
Properties:
• volatile liquid (evaporates quickly at room
temperature – more than water)
• colourless
• burns readily in air because of the
hydrocarbon chain
• good solvent
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Example question
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Mark scheme
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Uses of ethanol and methanol
Ethanol: biofuels, solvents, feedstock for
synthesis
Methanol: cleaner, feedstock for synthesis
Feedstock is the name we give to an
“ingredient” on a chemical plant
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Reactions of different functional
groups
• This is illustrated very well by comparing the
reaction of sodium with ethanol, hexane and
water.
• You have seen this reaction. Fill in the
following table and compare with the mark
scheme:
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Observations with sodium
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Mark scheme
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Comparing functional groups
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Mark scheme
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How do we make ethanol?
• Fermentation is a key process for obtaining
ethanol. It is relatively cheap and requires
wheat or beet sugar.
• The process involves the anaerobic respiration
of yeast at temperatures between 20 and 40°C
and at pH 7.
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Conditions for fermentation
• Outside an optimum temperature the yeast does not work (high
temperatures kill the yeast).
• Outside an optimum pH the yeast does not work (extremes of pH
kill the yeast).
• To make ethanol the yeast must respire anaerobically (without
oxygen).
• Eventually the ethanol concentration will be too high for the
fermentation to continue. This means only a dilute solution can be
made.
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Example question
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Example question
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Example question
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How do we obtain a concentrated
solution?
• Ethanol has a different boiling point to water.
We can therefore separate water and ethanol
using distillation.
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Example question
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Mark scheme
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Making ethanol using ethane from
crude oil
Ethane to ethene by
CRACKING
C2H6  CH2=CH2
• zeolite catalyst OR
• heat
Ethene to ethanol by
reaction with STEAM
CH2=CH2 + H2O 
CH3CH2OH
47
• phosphoric
acid catalyst
Example question
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Mark scheme
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Working out masses
• We can use the useful relationship
Mass1 Mass2
=
Mr1
Mr2
• Where Mr is the molecular mass
• eg Mr of ethane C2H6 is (2 X 12) + (6 x 1) = 30
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Example question
51
Explanation
• In this question every ethene molecule that reacts
makes one molecule of ethanol.
• We need to relate the number of molecules to mass
using our equation.
Mass1 Mass2
=
Mr1
Mr2
•
•
•
•
52
Mass 1 is mass of ethene = 1 tonne
Mr 1 is Mr of ethene = 28
Mass 2 is mass of ethanol = ?
Mr 2 is Mr of ethanol = 46
Mark scheme
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Example question
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Other alternatives
• Ethanol has also been synthesised using
genetically modified e-coli bacteria and sugars
from seaweed.
• This process is sustainable as the seaweed and
bacteria are renewable sources
• Like yeast, bacteria can be killed by high
concentrations of alcohol and high
temperatures
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Example question
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Mark scheme
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Ethanol – Key facts
• Ethanol is made on an industrial scale as a fuel, a
solvent and as a feedstock for other processes;
• There is a limit to the concentration of ethanol solution
that can be made by fermentation and there are
optimum conditions of pH and temperature.
• Ethanol solution can be concentrated by distillation to
make products such as whisky and brandy;
• Genetically modified E. coli bacteria can be used to
convert waste biomass from a range of sources into
ethanol and recall the optimum conditions for the
process;
• Ethane from crude oil can be converted into ethanol
• Evaluating the sustainability of each process is
59 important.
Bioethanol cycle
Plants
photosynthesise
•Remove CO2 from
atmosphere
Replanting
Fermentation
•Photosynthesis
removes CO2
•produces ethanol fuel
Burning
•Releases CO2 into
atmosphere
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Balancing carbon cycle equations
• Glucose (a simple sugar) is created in the plant
by
.
• Can you balance the following equation for
photosynthesis?
6 CO2 + 6 H2O → C6H12O6 + 6 O2
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Balancing carbon cycle equations
During ethanol
, glucose is
decomposed into ethanol and carbon dioxide.
Can you balance this equation?
C6H12O6 → 2 CH3CH2OH+ 2 CO2
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Balancing carbon cycle equations
During
ethanol reacts with oxygen
to produce carbon dioxide, water, and heat:
Can you balance this equation?
CH3CH2OH + 3 O2 → 2 CO2 + 3 H2O
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Carboxylic acids
C7.1
64
What do I need to know?
1. understand that the properties of carboxylic acids are
due to the presence of the –COOH functional group;
2. recall the names and formulae of methanoic and
ethanoic acids;
3. recall that many carboxylic acids have unpleasant
smells and tastes and are responsible for the smell of
sweaty socks and the taste of rancid butter;
4. understand that carboxylic acids show the
characteristic reactions of acids with metals, alkalis
and carbonates;
5. recall that vinegar is a dilute solution of ethanoic acid.
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Can you recognise the functional
group?
• Circle which of these is a carboxylic acid?
66
Answer
• This is a carboxylic acid
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Methanoic and Ethanoic
Methanoic acid
Ethanoic acid (VINEGAR)
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Acids in nature
Many acids are part of life itself, they are known as CARBOXYLIC acids
Organic or CARBOXYLIC
acids are part of life
itself and can be found
in many animals and
plants.
69
Reactions of carboxylic acids
Reaction of carboxylic acids
1) Acid + metal  salt + hydrogen
Ethanoic acid + magnesium  magnesium ethanoate + hydrogen
2) Acid + metal oxide  salt + water
Ethanoic acid + copper oxide  copper ethanoate + water
3) Acid + metal carbonate  salt + water +
carbon dioxide
Ethanoic acid + sodium carbonate  sodium ethanoate + water + carbon
dioxide
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Example Question
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Example question
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Example question
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Esters, Fats and Oils
C7.1
77
What do I need to know?
1. Recall the method for producing an ester
using reflux
2. Describe how fats and oils are all types of
ester and explain how margarine is made
3. Explain how bromine water can be used to
test whether a fat is saturated or unsaturated.
78
Making esters
What type of organic chemicals do you need to
mix together?
Can you name the ester made from ethanoic
acid and methanol?
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Making esters
What type of organic chemicals do you need to
mix together?
• A carboxylic acid and an alcohol with an acid
catalyst
Can you name the ester made from ethanoic
acid and methanol?
• Methyl ethanoate
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Esters
81
Example question
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Mark scheme
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Making esters
Reflux
84
Distillation
Purification
Drying
Reflux apparatus
85
How do I describe reflux for an
exam?
1. Mixture heated in flask (1) …
2. with condenser above (1) …
3. so no liquid is lost by evaporation and allows
longer time for the reaction (1)
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Distillation
87
Describing distillation
1. The mixture is heated
2. At the boiling point of the ester is becomes a
vapour
3. The vapour is condensed in the condenser
4. The liquid is collected
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Purification
1. Collected ester is shaken in a separating
funnel with distilled water.
2. Impurities dissolve in the water
3. Impurities are tapped off
Ester
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Drying
1. Solid drying agent is added to the product
2. This could be calcium chloride or sodium
sulphate
3. This removes water from the product
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Example question
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Mark scheme
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Example question
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Mark scheme
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Example question
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Mark scheme
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Fats and oils
• These are a special type of ester made from
glycerol and fatty acids.
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Fats and oils
• Removal of water in the condensation
reaction makes a fat or oil
98
Saturated or unsaturated?
• Have you heard these terms on the television?
• Vegetable oil is mostly unsaturated
• Animal fat is mostly saturated
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Double bonds or not
• A saturated fat has no
C=C double bonds
(alkene functional
groups) and is usually a
solid fat like margarine
or animal fat.
• An unsaturated fat has
C=C double bonds and
is usually an oil like
vegetable oil.
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Example question
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Mark scheme
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Making margarine
• To make margarine we have to saturate
vegetable oil by bubbling hydrogen gas
through the oil.
• This process is called hydrogenation
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Is a fat or oil saturated or not?
• We can test for this by adding bromine water.
• If there are double bonds present the bromine
water changes from
to
.
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Example question
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Mark scheme
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Hydrolysis
• When an ester is hydrolysed it goes back to an
acid and alcohol
• We can hydrolyse by adding acid or alkali
(NaOH).
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Example question
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Mark scheme
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Energy changes in chemistry
C7.2
110
Quiz
• When a chemical reaction takes place heat
may be given out or taken in.
1. Can you remember the word we use when
heat is given out?
2. Can you remember the word we use when
heat is taken in?
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What do I need to know?
1. Recall and use the terms ENDOTHERMIC and
EXOTHERMIC
2. Describe examples of ENDOTHERMIC and
EXOTHERMIC reactions.
3. Use simple energy level diagrams to
represent ENDOTHERMIC and EXOTHERMIC
reactions.
112
Change in energy
• Chemical reactants have a certain amount of
stored within them.
• When the reaction has taken place they have
either
within them
than before.
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Definitions
(exothermic) then the
than they did before.
They have lost it to the surroundings.
(endothermic) then the
than they had
before. They have taken it from the
surroundings.
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Energy level diagrams
Which diagram do you think is
which is
?
Heat taken in
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Heat given out
and
Energy level diagrams
Endothermic
Exothermic
Heat taken in
Energy level of products is higher
than reactants so heat taken in.
116
Heat given out
Energy level of products is lower
than reactants so heat given out.
Example question
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Mark scheme
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Bond enthalpies
C7.2
119
Quick quiz
1. Reactions where the products are at a lower energy
than the reactants are endothermic (TRUE/FALSE)
2. Activation energy is the amount of energy given out
when a reaction takes place (TRUE/FALSE)
3. A reaction which is exothermic transfers heat energy
to the surroundings (TRUE/FALSE)
4. How can we tell if a reaction is exothermic or
endothermic?
5. Sketch the energy profile for an endothermic
reaction.
6. When methane (CH4) burns in oxygen (O2) bonds
between which atoms need to be broken?
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Answers
1.
2.
3.
4.
5.
6.
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Reactions where the products are
at a lower energy than the
FALSE
reactants are endothermic
(TRUE/FALSE)
Activation energy is the amount
of energy given out when a
FALSE
reaction takes place
(TRUE/FALSE)
A reaction which is exothermic
transfers heat energy to the
TRUE
surroundings (TRUE/FALSE)
How can we tell if a reaction is
exothermic or endothermic? Measure the
Sketch the energy profile for an
endothermic reaction.
When methane (CH4) burns in
oxygen (O2) bonds between
which atoms need to be broken?
temperature change
C—H bonds and O=O bonds
What do I need to know?
1. Recall that energy is needed to break
chemical bonds and energy is given out when
chemical bonds form
2. Identify which bonds are broken and which
are made when a chemical reaction takes place.
3. Use data on the energy needed to break
covalent bonds to estimate the overall energy
change for a reaction.
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Activation energy revisited
• What is the activation energy of a reaction?
• The energy needed to start a reaction.
• BUT what is that energy used for and why
does the reaction need it if energy is given out
overall?
• The activation energy is used to break bonds
so that the reaction can take place.
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Burning methane
Consider the example of burning methane gas.
CH4 + 2O2  CO2 + 2H2O
This reaction is highly exothermic, it is the
reaction that gives us the Bunsen flame.
However mixing air (oxygen) with methane is
not enough. I need to add energy (a flame).
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What happens when the reaction gets
the activation energy?
H H H H
Energy in chemicals
C
O
Bond
Breaking
H
C
H
H
H
O
O
O
Bond
Forming
O
O
O
O
O
H
O
Progress of reaction
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C
O
H
O
H
H
Using bond enthalpies
By using the energy that it takes to break/make
a particular bond we can work out the overall
enthalpy/energy change for the reaction.
Sum (bonds broken) – Sum (bonds made) =
Energy change
126
BIN MIX
Breaking bonds is ENDOTHERMIC energy is
TAKEN IN when bonds are broken
Making bonds is EXOTHERMIC energy is GIVEN
OUT when bonds are made.
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Bond enthalpies
Bond
Bond enthalpy (kJ)
Bond
Bond enthalpy (kJ)
C—H
435
Cl—Cl
243
C—C
348
C—Cl
346
H—H
436
H—Cl
452
H—O
463
O=O
498
C=O
804
C=C
614
128
Can you work out the energy change
for this reaction?
129
The answer is -120 kJ
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Example question part 1
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Question part 2
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Question part 3
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Mark scheme
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Challenge question
• The true value for the energy change is often
slightly different from the value calculated
using bond enthalpies.
• Why do you think this is?
135
Example question
The calculated value is 120 kJ
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Mark scheme
137
Definitions
Write each of these phrases in your book with a
definition in your own words:
•
•
•
•
•
138
Exothermic reaction
Endothermic reaction
Activation energy
Catalyst
Bond energy/enthalpy
How did you do?
Exothermic reaction
A reaction which gives energy out to the surroundings.
Endothermic reaction
A reaction which takes in energy from the surroundings.
Activation energy
The energy required to start a reaction by breaking bonds in the
reactants
Catalyst
A substance that increases the rate of a reaction by providing an
alternative pathway with lower activation energy. It is not used up in
the process of the reaction
Bond energy/enthalpy
The energy required to break a certain type of bond. The negative
value is the energy given out when that bond is made.
139
Popular exam question
1. Explain why a reaction is either exothermic or
endothermic?
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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Popular exam question
1. Explain why a reaction is either exothermic or
endothermic?
141
① In a chemical reactions some bonds are broken and
some bonds are made.
② Breaking bonds takes in energy.
③ Making bonds gives out energy.
④ If the energy given out making bonds is higher than
the energy needed to break them the reaction is
exothermic.
⑤ If the energy needed to break bonds is higher than the
energy given out making them the reaction is
endothermic.
Chemical Equilibria
C7.3 Reversible Reactions &
Dynamic Equilibria
142
What do I need to know?
1. State that some chemical reactions are
reversible
2. Describe how reversible reactions reach a
state of equilibrium
3. Explain this using dynamic equilibrium
model.
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Reversible or not reversible
Until now, we were careful to say that most
chemical reactions were not reversible –
They could not go back to the reactants
once the products are formed.
144
Example
In the case of the vast majority of chemical
reactions this is true, the reaction of
methane and oxygen for example:
It is almost impossible to return the carbon
dioxide and water to the original methane
and oxygen.
145
Reversible
• Some chemical reactions, however, will go
backwards and forwards depending on the
conditions.
• CoCl2·6H2O(s)  CoCl2(s) + 6H2O(l)
pink
blue
146
How do we write them down?
• This is the symbol for used for reversible
reactions.
CoCl2·6H2O(s)
147
CoCl2(s) + 6H2O(l)
What is equilibrium?
• Reversible reactions reach a balance point,
where the amount of reactants and the
amount of products formed remains
constant.
148
Dynamic Equilibrium.
• In
the forward and
backwards reactions continue at equal rates
so the concentrations of reactants and
products do not change.
• On a molecular scale there is
.
• On the macroscopic scale
. The system needs to be closed
– isolated from the outside world.
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Example question
150
Mark scheme
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Dynamic Equilibria
C7.3 Controlling equilibria
152
What do I need to know?
1. Recall that reversible reactions reach a state
of dynamic equilibrium.
2. Describe how dynamic equilibria can be
affected by adding or removing products and
reactants.
3. Explain the difference between a “strong” and
“weak” acid in terms of equilibria
153
Position of the equilibrium
• Equilibrium can “lie” to the left or right.
• This is “in favour of products” or “in favour of
reactants”
• Meaning that once equilibrium has been
reached there could be more products or
more reactants in the reaction vessel.
154
Le Chatelier’s principle
• If you remove product as it is made then
equilibrium will move to the right to counteract
the change
• If you add more reactant then equilibrium will
move to the right to counteract the change.
• In industry we recycle reactants back in and
remove product as it is made to push the
equilibrium in favour of more product.
155
Complete
When a system is at__________ to make more
product you can_________ product or add more
__________ for example by recycling them back
in.
To return to reactants you ______ product or
remove_________.
[equilibrium, add, reactant, remove, product]
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Strong and weak acids
A strong acid is one which is FULLY IONISED in water. It
will have a high hydrogen ion concentration
A weak acid is one which is NOT fully ionised and is in
equilibrium. It has a low hydrogen ion concentration
Caution – weak and strong are not the same as concentration.
157
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Mark scheme
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Example question
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Mark scheme
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Practicing definitions
Write each of these phrases in your book with a
definition in your own words:
•
•
•
•
•
162
Reversible reaction
Dynamic equilibrium
Position of equilibrium
Strong acid
Weak acid
How did you do?
Reversible reaction
A reaction that can proceed in the forward or reverse directions (represented
by two arrows in an equation).
Dynamic equilibrium
The point where the rate of the forward reaction = rate of the reverse
reaction.
Position of equilibrium
The point where there is no further change in the concentration of either
reactants or products. The position can lie to the left (favouring reactants) or
right (favouring products).
Strong acid
An acid that is completely dissociated in water
Weak acid
An acid that is only partly dissociated in water because the reaction is in
dynamic equilibrium and favours the reactants (LHS).
163
Popular exam question
1. Ethanoic acid (CH3COOH) is a weak acid but
hydrochloric acid is a strong acid. Use ideas
about ion formation and dynamic equilibrium
to explain this difference.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------164
Popular exam question
Ethanoic acid (CH3COOH) is a weak acid but hydrochloric acid is a
strong acid. Use ideas about ion formation and dynamic
equilibrium to explain this difference.
① Hydrochloric acid ionises completely
② So hydrogen ion concentration is high
③ Ethanoic acid only partly dissociates because the reaction
is reversible
④ Equilibrium is mainly to the left
⑤ So hydrogen ion concentration is low.
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