Topic 8 – National 4 Chemistry Summary Notes
Everyday Consumer Products
In this topic you will learn about two new groups of compounds called alcohols and
carbohydrates.
Carbohydrates from Plants
LI 1
Carbohydrates are a high energy group of compounds that are made by plants through a
process called PHOTOSYNTHESIS.
Carbohydrates are high energy compounds which contain carbon, hydrogen and oxygen.
They include substances you might have heard about called sugars and starch.
Carbohydrates are important to us because they provide energy for us in many foods
and can be burned as fuels.
There are many plants that supply us with carbohydrates:
Type of Food
High in Sugar
(tick)
High in Starch
(tick)
Crisps
Plant Source
potatoes
Fruit juice
Pasta
Cereal bars
Bread
wheat
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LI 2
Formulae of Carbohydrates
The two main carbohydrates we are interested in are the simple carbohydrate called
glucose and the complex carbohydrate called starch.
All carbohydrates contain carbon, hydrogen and oxygen with a ratio of hydrogen and
oxygen of 2:1.
Glucose is described as a simple carbohydrate because it is a small molecule with the
formula:
C6H12O6
Glucose
Starch is described as a complex carbohydrate because it is formed by joining many
glucose molecules together:
Plants convert glucose into starch for storing energy.
Activity- carry out solubility tests on starch and glucose and then see if you can explain
why plants store energy as starch not as glucose:
Results
Starch_____________ dissolve well in water but glucose _________. Plants do not
store glucose because when it rains
________________________________________________________________
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LI 3
Chemical Tests For Carbohydrates
Starch and glucose are both white powders full of chemical energy. We know that
starch is insoluble and glucose is soluble but there are other tests we can do to
distinguish between starch and glucose:
The Benedict’s Test
If a blue solution called Benedict’s solution is added to a carbohydrate solution and it is
then heated in a hot water bath the solution will turn orange only if sugar is present
and glucose is a sugar. ( other sugars like fructose also change Benedict’s orange)
Starch has no effect on Benedict’s solution.
The Iodine Test
If a carbohydrate is tested with iodine solution the brown iodine will turn blue/black
only if starch is present!
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Summary of Properties of Starch and Glucose
Type of
Carbohydrate
Starch
Formula
Solubility
Reaction with
Iodine
Reaction with
Benedicts
Glucose
LI 4
Breaking Down Starch
Starch is a high energy compound but although it is in food we cannot use it directly in
our cells for energy. The starch must be broken back down into glucose so that it can
be transported around the body and get into our cells. This break down of starch
happens in your digestive system and is part of the digestion process.
The Model Gut Experiment
You will carry out an experiment to prove that only glucose is small enough to pass
through the gut wall and on into the bloodstream. Draw a labelled diagram below of the
method you used:
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The Amylase Experiment
You will carry out an experiment to prove that starch is broken down into simple sugar
during digestion, in your gut, by an enzyme called amylase. Enzymes are biological
catalysts used by your body to speed up reactions. The type of reaction that breaks
starch down is called HYDROLYSIS.
Draw a labelled diagram below to show the method you used:
Acid Hydrolysis
Starch can also be broken down by heating with acid. Your teacher will demonstrate it.
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LI 5
Getting Energy Out Of Glucose
Once in body cells the glucose molecules release their energy by going through a
process called RESPIRATION.
We would not normally show energy as a product in a reaction, it isn’t a substance, but
we have left it in to emphasise that respiration is all about releasing energy from food.
Respiration is the opposite of photosynthesis
Making Alcohol
LI 6
Making alcohol 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. The process
for making alcohol is called FERMENTATION where enzymes present in yeast are
responsible for converting glucose into ethanol.
These alcoholic drinks all contain the alcohol called ethanol but have many other flavour
molecules to give distinctive drinks:
Type of alcoholic drink
Whisky
Plant source of carbohydrate
Barley
Beer
Wine
Cider
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Percentage Alcohol
Content
Fermentation
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
_________________________.
Q. How can we prove we have made ethanol?
Answer- Ethanol has a lower boiling point than water ( 78 °C) 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.
Distillation apparatus
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LI 7
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”. Enzymes in yeast work best at around body temperature of 37 0C
and a pH of about 7.
Units of Alcohol
LI 8
As mentioned ethanol is a poison and it is important not to take too much. You will
research as a home work how many units of alcohol we should be drinking and what
volume of each drink contains one unit of alcohol:
Alcoholic Drink
Alcohol Content %
What volume equals ONE
unit (cm3)
Whisky
Gin
Beer
Vodka
Wine
There are many health issues associated with drinking too much alcohol. Write below
two of the issues that you think are most important:
1.
2.
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Carbohydrates as Food or Fuel?
LI 9
http://en.wikipedia.org/wiki/Food_vs._fuel
Food vs. fuel is a big concern regarding the risk of using farmland or crops for biofuels production
instead of for food supply on a global scale. The "food vs. fuel" or "food or fuel" debate is an
international one.
There is disagreement about how significant the issue is, what is causing it, and what can or should
be done about it.
Using the link above to start you off you will research this issue by answering the questions below to
help you.
1. Name two crops that could be used as biofuels.
2. Which country( in South America) relies heavily on Bioifuels.
3. What does it grow in order to make the biofuel ethanol.
4. What affect does using so much land to produce biofuels seem to have on food
prices.
5. What crops does the UK grow in order to make biofuels.
6. In your reading did you find any other problems with using so much land for
biofuels?
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Topic 8 National 4 – Pupil Self-evaluation
Learning Intention
Success Criteria
“ I can:”
1
I am going to find out that
plants are a source of
carbohydrates which can be
used for fuels or food
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Name two plants that provide carbohydrates
Name two foods high in starch
Name two foods high in sugar
2
I am going to find out about
the formulae of
carbohydrates

State that carbohydrates are compounds containing the elements
carbon hydrogen and oxygen in a ratio of 2:1 “H” to “O and C”
State that starch is a complex carbohydrate
State that glucose is a simple carbohydrate
State that starch is formed from many glucose molecules
State that Starch is insoluble so it can be stored safely in plants
State that glucose is very soluble so could be easily washed away
I can draw a labelled diagram to show how Benedicts can be used to
test for simple sugars
I can give the colour change when Benedicts reacts with simple sugars
I can give the colour change when Iodine reacts with starch
State that enzymes are biological catalysts
State that digestion produces small, soluble molecules like glucose, that
can pass through the gut wall then into the bloodstream and on into
cells
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4
I am going to find out about
the chemical tests for
carbohydrates
I am going to find out that
in our gut we use acid and
enzymes to help hydrolysis
reactions go fast and that
digestion of starch is an
example.
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6
I am going to find out about
the process called
respiration
I am going to find out how
enzymes in yeast convert
glucose to ethanol in a
process called fermentation
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I am going to find out that
enzymes only work well
under certain conditions
I am going to find out about
the alcohol content of
different drinks and discuss
health issues associated
with drinking too much
alcohol.
I am going to research the
issues around using
carbohydrates as fuel as
well as fuel
State that respiration is a process that the cells in our body use to get
energy out of glucose
State that the products of respiration are water and carbon dioxide
State that alcohol is produced in a fermentation reaction
Describe what “enzyme optimal conditions” means
State that enzymes stop working when the concentration of alcohol
gets too high
Give examples of different plants used to make alcoholic drinks
State that distillation is a process used to separate liquids of different
boiling points

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State that the word optimal mean the best
State that pH and temperature affect enzyme activity

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State the units of alcohol in wine, beer and spirits
State two serious health issues brought on by drinking too much alcohol
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Give examples of two crops used as both food and fuel
Give a disadvantage of using so much land to produce crops for fuel
rather than food
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