Unit 6
Plants and
Fertilisers
Sugars
Starch, sugar and alcohol are all linked in
some way, the first two are both
carbohydrates, carbohydrates undergo
fermentation (chemical process) to become
the alcohol found in drinks (beer, wines,
spirits).
Plants, Sugars and Sunlight
All plants make sugars in their leaves. To do
this they use the energy they get from
sunlight. This sugar is called GLUCOSE.
The sugar that you put on your cereal and
use to bake with i.e. table sugar is a sugar
called SUCROSE.
Some plants can convert the glucose they
make into sucrose. These plants are sugar
cane and sugar beet.
Sugar cane
Sugar beet
Some plants convert the glucose into
another sugar called FRUCTOSE, this is
common in plants which produce fruits,
hence the sugar’s name.
Another type of sugar is MALTOSE which is
produced in germinating cereals such as
barley. This is the sugar which is used in the
brewing process (i.e. the making of beer).
The sugar LACTOSE is produced by
animals and it is found in the milk of the
animal, including human milk, hence why it
is sometimes known as milk sugar.
Sugar properties
Properties
Appearance
Taste
Solubility
pH
Conduction
Glucose Sucrose Fructose Maltose Lactose
Think about the results for the conductivity
of sugars. What do you think the bonding in
sugars is, ionic or covalent?
Covalent
Why do you think this?
There are no ions in covalent bonding.
What were the similarities and differences
between the five sugars?
Similarities
Differences
Testing with Benedict’s Solution
Benedict’s solution can be used to test for
some sugars. The positive test for sugars with
Benedict’s is when the Benedict’s solution
turns from blue to a reddish, brown colour
(although dark mustard yellow and orange
count as a positive result).
Try the following experiment:
 Take five test tubes and place ½ a spatula of
glucose in one test tube, ½ a spatula of sucrose in
one, ½ a spatula of fructose in one, ½ a spatula of
maltose in one and ½ a spatula lactose in the last
tube.
 Label the test tubes, so the sugars do not get
mixed up.
 Place roughly 150cm3 of hot water into a 250cm3
beaker, this is used as a water bath.
 Add a depth of 2cm of water in the test tubes and
shake the tubes.
 Add 10 drops of Benedict’s to the test tubes and
place them in the water bath for five minutes and
record the results.
Sugar
Glucose
Sucrose
Fructose
Maltose
Lactose
Result with Benedict’s Solution
Which sugar can you NOT use Benedict’s
solution to test for?
Elements in Sugar
All sugars contain the same elements – just in
a different structure. These elements can be
identified by heating the sugar.
Carry out the following experiment to find
out what elements are in sugars:
 Collect a dry test tube, tongs, Bunsen burner,
sucrose and a small piece of blue cobalt chloride
paper.
 Add one spatula of sucrose into the test tube and
heat for a few seconds in a quiet blue flame.
Remember and hold the tube horizontally.
 Move tube away from the flame when
condensation is seen and test the condensation
with the blue cobalt chloride paper.
 Place test tube back in the flame and leave the
sugar until it is roasted.
The cobalt chloride paper turns from blue to
___________, this occurs in the presence of
______________ which is made up of
___________ and _____________.
The element that remains in the burnt black
solid is________; this is the same element
that is present when you burn your toast.
All sugars are made up of the same three
elements, as the name of the group they
belong to suggests: carbohydrates.
CARBO
HYDR
ATE
carbon
hydrogen
oxygen
Sugar Molecules
Single Unit Sugars (Simple Units)
Glucose and fructose are classed as simple
sugars. These molecules are quite complicated
to draw so it is easier simplifying the diagram
by using a block to represent the main part of
the molecule and only draw the atoms which
take part in reactions.
When using these simply diagrams, use
different colours to distinguish between
glucose and fructose.
The chemical formula for glucose and
fructose are C6H12O6.
The difference between the glucose and
fructose is the structure of the molecules.
Double Unit Sugars
Double unit sugars are formed when two
single unit sugars join together:
When the two single unit sugars join
together to form the double unit sugar some
atoms have to be lost. These atoms then
join up and form a small molecule:
The formula for double unit sugars: sucrose,
maltose and lactose is C12H22O11.
The number of carbon atoms in a double unit
is 2x the number in a single unit – hence the
name double!
Sugar units are called saccharides by
scientists.
Single unit sugars can also be called a
monosaccharide (mono means one).
Double unit sugars can also be called
disaccharides (di means two).
Remember:
Isomers: molecules with the same
molecular formula but different
structural formulas