Topic 8 – National 5 Chemistry Summary Notes
Everyday Consumer Products
In this topic you will learn about two new homologous series of compounds called
alcohols and carboxylic acids and how they can be used to make an important group of
compounds called esters.
Alcohols from Carbohydrates
LI 1-4
When we talk about alcoholic drinks we really mean drinks containing a particular
member of the alcohol family called ethanol.
Ethanol is generally made by a process called fermentation. Fermentation is brought
about by enzymes in yeast which convert the simple sugar called glucose into ethanol.
Glucose is part of a large family of compounds called carbohydrates. Carbohydrates
contain the elements carbon, hydrogen and oxygen with a ratio of 2:1,
hydrogen:oxygen. As you have learnt about in earlier science topics, plants are a source
of carbohydrates and the main carbohydrate found in plants is starch. Starch is the
ideal way for plants to store energy. It is insoluble so cannot be washed away but this
large, insoluble and complex carbohydrate, is broken down easily by enzymes to form
glucose a small, simple sugar molecule which dissolves easily. This type of reaction uses
the addition of water to break down large molecules and is called hydrolysis.
This same hydrolysis reaction breaks down many compounds in our digestive
systems using acid and enzymes so that small soluble molecules can be made and
easily passed through the gut wall and on into our cells.
Remember!!- Enzymes are biological catalysts used by living things to make reactions
go faster. A good example of an enzyme is the catalyst amylase, used to break starch
down into simple sugars.
Summary of Properties of Starch and Glucose
Type of
Carbohydrate
Formula
Solubility
Starch
Glucose
1
Reaction with
Iodine
Reaction with
Benedict’s
LI 5&6
Fermentation
Fermentation is big business in Scotland! There are nearly 20,000,000 barrels of
whisky sitting maturing in warehouses at any one time all made by fermenting barley.
Many different alcoholic drinks are made from different plant sources. They all contain
the alcohol called ethanol but have many other flavour molecules to give distinctive
drinks:
Type of
alcoholic drink
Whisky
Beer
Wine
Cider
Plant source
of carbohydrate
Barley
Alcohol Content
(%)
We can make ethanol by fermentation in the school laboratory:
C6H12O6
2C2H5OH
+
2CO2
glucose
ethanol
+ carbon dioxide
We can prove we made carbon dioxide by bubbling it through limewater because it will
_________________________.
How can we prove we have made ethanol?
Answer- Ethanol has a lower boiling point than water ( 78⁰C) so we can separate it out
by distillation and show that it burns. Ethanol burns very well. (it also smells!!)
The maximum % of alcohol we can produce by fermentation is around 14% because the
ethanol is a poison and yeast, a living organism, is killed by high levels of ethanol.
Distillation has to be used to produce drinks of a higher alcohol content.
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Enzyme Optimal Conditions
Not only do high levels of ethanol stop yeast working, the activity of the enzymes in
yeast ( and all enzymes) are easily affected by the conditions they are working in. They
are sensitive to changes in temperature and pH and work best within a narrow range of
pH and temperature. Each individual enzyme has its own set of ideal conditions called
“optimal conditions”.
Units of Alcohol
As mentioned ethanol is a poison and it is important not to take too much. You will
research as a homework how many units of alcohol we should be drinking and what
volume of each drink contains one unit of alcohol:
Alcoholic Drink
Alcohol Content
%
whisky
gin
beer
vodka
wine
3
What volume equals
ONE unit (cm3)
LI 7
Structure and Functional Group of Alcohols
Ethanol is the second member of a homologous series of alcohols known as alkanols
because they are based on the alkane structure.
As well as by fermentation ethanol can be made by an addition reaction called
“hydration” when a molecule of water is added to the unsaturated ethene molecule.
This sort of reaction requires high temperatures and pressure and a phosphoric acid
catalyst:
Names and structures of alkanols can easily be worked out because they are closely
related to the corresponding alkane. A hydrogen has been replaced by a new functional
group ( –OH) called the hydroxyl group and the name of the alkane has the ―e‖ removed
and an ― ol‖ substituted.
Name of
alcohol
Molecular formula
of alcohol
methanol
CH3OH
ethanol
C2H5OH
propanol
C3H7OH
Structure formula of
alcohol
From this table you can work out the general formula of the alkanols:
CnH2n+1OH
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LI 8
Drawing and Naming Alkanols
All alkanols with more than 2 carbons have isomers and therefore have different names
due to the position of the hydroxyl group:
propan-1-ol
propan-2-ol
Shortened structural formulae also show the different positions of the hydroxyl
groups:
Propan-1-ol
-
CH3CH2CH2OH
Propan-2-ol
-
CH3CH(OH)CH3
Systematic naming rules:
1. Count the number of carbons to give the correct basic name ie
4 carbons = butanol
5 carbons = pentanol
etc…
2. Count from the end which gives the lowest number to show the position of the
hydroxyl group.
NOTE- You will only be asked to name straight chained alkanols.
Activity: Complete the following table
Name of alkanol
Full structural formula
Butan-2-ol
Pentan-3-ol
5
Shortened structural
formula
Properties of Alkanols
LI 9
Alkanols are a homologous series therefore they have similar chemical properties and
gradually changing physical properties. We will look at physical properties first:
Boiling Points
Using the data booklet, page 6, fill in the following table:
Name of Alkanol
Methanol
Boiling Point (ºC)
Ethanol
Propan-1-ol
Butan-1-ol
There is a clear trend. The larger the molecule the higher the boiling point. This is
similar to what we discovered with the fractions of crude oil. The larger the molecule
the more energy is needed to separate the molecules from each other because larger
forces of attraction have to be overcome.
Boiling Points of Isomers
Using the data booklet, page 6, fill in the following table:
Name of Alkanol
Boiling Point (ºC)
Propan-1-ol
Propan-2-ol
Butan-1-ol
Butan-2-ol
Isomers have different boiling points. The position of the hydroxyl group has an
effect. If the hydroxyl group is at the end of a chain the boiling point is higher so the
force of attraction must be higher. The effect of the hydroxyl group can be seen even
more if you compare two molecules with similar formula mass:
Propane (formula mass 44) has a boiling point of (minus) - 44 ºC
Ethanol ( formula mass 46) has a boiling point of +78ºC due to the attractive force of
the hydroxyl group.
6
Solubility in water
Methanol and ethanol dissolve well in water, they mix completely and are described as
totally miscible.
As the hydrocarbon chain length increases, the solubility decreases so the bigger
alkanol molecules are less soluble in water.
Alkanol
Butan-1-ol
Pentan-1-ol
Hexan-1-ol
Heptan-1-ol
Octan-1-ol
Formula
C4H9OH
C5H11OH
C6H13OH
C7H15OH
C8H17OH
Solubility in water in g/l
63
22
5.9
1.7
0.5
Draw a spike bar graph of the number of carbon atoms in the molecule versus the
solubility in water and staple it to your booklet here.
pH of Alkanols
Alkanols have no effect on the balance between hydroxide ions and hydrogen ions in
water therefore the pH is neutral.
Uses of Alkanols
Ethanol is often used as an ingredient in industry to make other compounds. It is also
an important solvent in perfumes and food flavourings. Look in your kitchen cupboards
and see if you can find ethanol in the ingredient lists.
Propan-2-ol is also used as a solvent and you have probably used it to clean your
computer screen or in a gel to sanitise your hands. Remember alkanols are poisonous to
bacteria as well as us!
Chemical Properties of Alkanols
All alkanols burn, ethanol and methanol in particular burn very cleanly, we will be
investigating the uses of alkanols as fuels at the end of this topic.
Alkanols also take part in many other reactions. One very important reaction is
oxidation. This oxidation reaction increases the ratio of oxygen to hydrogen in the
molecule and converts an alkanol, with a hydroxyl group on an end carbon, into a new
homologous series of compounds called the carboxylic acids. This reaction naturally
occurs in wine when the ethanol reacts with oxygen in the air to form ethanoic acid
(vinegar). This is what turns wine sour.
7
LI 10
Carboxylic Acids
Carboxylic acids are a homologous series that all contain the functional group called the
carboxyl group:
If the carboxyl group is on an alkane chain then the name will be similar to the alkane it
comes from but with an ―oic‖ ending. This family of carboxylic acids are known as the
―alkanoic acids”.To work out the name just count the carbons:
Number of carbons
1
Name of
carboxylic acid
Methanoic acid
2
Ethanoic acid
3
Propanoic acid
4
5
Shown below is the full structural formula of the most well known carboxylic acid called
ethanoic acid (vinegar):
Ethanoic acid
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Structures of Carboxylic Acids
All alkanoic acids are an alkane chain with the last carbon converted to a –COOH.
To draw the structure of an alkanoic acid from its name work out the number of
carbons, fill them completely with hydrogen except for the last carbon which needs to
be double bonded to an oxygen and single bonded to an –OH group to form the carboxyl
group. Try these:
Name of
carboxylic acid
Shortened Structural
Formula
Propanoic acid
CH3CH2COOH
Butanoic acid
CH3CH2CH2COOH
Full Structural formula
CH3CH2CH2CH2COOH
LI 11
Carboxylic Acids in the Natural World
You will all have met carboxylic acids in everyday life. They are hard to miss because
they are a very smelly, stingy group of compounds. The best known are:
1. Methanoic acid (old name formic acid‖) is in ant and bee stings.
2. Lactic acid is what causes milk to go sour.
3. Citric acid is in fruit.
4. Vinegar, a dilute and smelly solution of ethanoic acid.
5. Vomit!!
Part of the reason vomit is so smelly is that some of the digestion products of fats are
brought back up. When fats are digested a special group of carboxylic acids called
fatty acids are made.
9
Uses of Vinegar
Read the extract below then answer the questions:
Vinegar’s role in history is well documented. This versatile product was used by
everyone—from kings and conquerors to explorers and everyday people.











The Babylonians used vinegar to preserve and pickle food.
Hippocrates prescribed vinegar as a remedy for a variety of ailments.
Caesar’s armies used vinegar as a beverage.
Hannibal drenched huge boulders in hot vinegar which cracked them into small
pieces, enabling his army to continue its journey across the Alps.
Helen of Troy bathed in vinegar to relax.
Jesus was offered vinegar before he was crucified.
Early Europeans used vinegar as a deodorizer.
During the Bubonic Plague people poured vinegar on their skin to protect
themselves from germs.
Cleopatra dissolved pearls in vinegar to prove that she could consume a fortune
in a single meal.
Sailors used vinegar as a food preservative during long voyages.
World War I medics used vinegar to treat soldiers’ wounds.
Today, people are still using white distilled vinegar in hundreds of different ways—from
cooking and cleaning to gardening and the laundry.
Q1. Vinegar is often used to remove lime scale. Lime scale is made of the same
substance that pearls are. Suggest why vinegar is able to dissolve lime scale.
Q2. Can you give two examples of foods we still preserve using vinegar.
Q3. Can you suggest why vinegar was used to treat wounds and why this might be linked
to its preservative effect.
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LI 12
Making Esters
One of the main industrial uses of carboxylic acids is to make compounds called esters.
Esters are an important group of carbon based compounds formed by reacting a
carboxylic acid molecule and an alcohol molecule together. The reaction requires a
catalyst such as concentrated sulphuric acid.
The "ester link"
Word equation:
methanol
+ butanoic acid
⇄
methyl butanoate (ester)
+ water
CH3OH
+ C3H7COOH
⇄
C3H7COOCH3 (ester)
+
H2O

The characteristic link between the molecules is called the ester link

This type of reaction is called a condensation reaction

Condensation reactions are reactions which join two molecules together
by releasing a small molecule, often water

A condensation reaction that makes an ester is also called esterification

Condensation reactions are reversible

The name of the ester comes from the alcohol and carboxylic acid that
made it with the alcohol part coming first
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Names of Esters
Identify the names of the alcohol and the carboxylic acid used to make the
ester, change the endings and add them together:
Alcohol
Name
methanol
ethanol
propanol
butanol
LI 13
Ester
Name
methyl……
ethyl…..
propyl….
butyl…..
Carboxylic Acid
Name
methanoic acid
ethanoic acid
propanoic acid
butanoic acid
Ester Name
……methanoate
…..ethanoate
…..propanoate
…..butanoate
Properties and Uses of Esters
Esters can be made easily in the lab.
Once they are made they are identified due to their characteristic fruity smells and
the fact that they do not mix with water and form an oily, immiscible layer.

Esters are often used as food flavourings

Esters are often used as perfumes

Many nail varnishes contain ester solvents because they easily evaporate
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