C3 – Unit 5

The Carbon Cycle

A Chemical Test for Starch

6 carbohydrates were dissolved in water – glucose, fructose, lactose, maltose, sucrose and starch.


A few drops of each was removed and put on a dimple tile.


Three drops of iodine solution was placed on each carbohydrate.


The starch turned black – this is the chemical test for starch – iodine gives a blue/black colour.



An internet search was carried out to find a definition for photosynthesis.

The process in green plants and certain other organisms by which carbohydrates are synthesized from carbon dioxide and water using light as an energy source. Most forms of photosynthesis release oxygen as a byproduct.



Discs were cut out of leaves using cork borers.

The discs were boiled in water for five minutes to burst the plant cells.

They were transferred to a test-tube and ethanol added and the boiled in a water bath for a couple of minutes. This removed the green colour (chlorophyll).

The discs were transferred back to the water for a couple of minutes and then placed in a dimple tile and iodine solution added.

Discs A and B were from green leaves, disc C from a pale leaf.

The green leaves contained starch.

Green plants use the sun’s energy to react carbon dioxide and water and form glucose and oxygen. This is known as photosynthesis. The chlorophyll allows the suns energy to be captured.

6CO2+ 6H2O → C6H12O6 + 6O2

The glucose is then stored by the plant as starch.


Combustion of carbohydrates – here paper (cellulose) soaked in sugar (sucrose) and dried.

The paper was burned and the products of combustion drawn through a cooled U tube and then through a bubbler filled with lime water.

Condensation formed in the U tube showing water was produced

And the lime water turned cloudy showing carbon dioxide had formed

(Thanks Rachael for the pictures)

Carbohydrates burn to produce carbon dioxide and water

C6H12O6 + 6O2 → 6CO2 + 6H2O

This also shows that carbohydrates must contain the elements carbon and hydrogen.


Researched the formulas and sources of a variety of carbohydrates

glucose (C6H12O6 ) found in most plants

fructose (C6H12O6 ) found in fruits

maltose (C12H22O11 ) found in sprouting grains

sucrose (C12H22O11 ) found in cane sugar

lactose (C12H22O11 ) found in milk

starch ((C6H10O5)n) found in potatoes, rice, pasta, etc

Glucose and fructose are known as isomers. They have the same chemical formulas but different arrangements of atoms. Sucrose, maltose and lactose must also be isomers.



An internet search was carried out to find a definition for respiration.

The oxidative process occurring within living cells by which the chemical energy of organic molecules is released in a series of metabolic steps involving the consumption of oxygen and the liberation of carbon dioxide and water.



1. To show that carbon dioxide is produced during respiration – breathing was done through lime water

The lime water for exhaled air went cloudy – we breathe out carbon dioxide.


2. To show that oxygen is used up in respiration

The same air in a gas jar was breathed four times. A lit splint was put into the gas jar.

Respiration is the opposite of photosynthesis. It is basically the same chemical reaction as the combustion looked at last lesson.

C6H12O6 + 6O2 → 6CO2 + 6H2O

Properties of carbon dioxide

Carbon dioxide can be prepared by reacting marble chips (calcium carbonate) with hydrochloric acid.


1) Lime water

Lime water turns cloudy as carbon dioxide reacts with it.

Lime water is calcium hydroxide.


Ca(OH)2(aq)  +  CO2(g)  →  CaCO3(s)  +  H2O(l)


The calcium carbonate formed is a precipitate (a solid forming in a liquid).


2) pH

Carbon dioxide was added to water along with some universal indicator.

This gave an orange red colour. Carbon dioxide is an acidic gas.


CO2  +  H2O  →   H2CO3

carbonic acid.


3) Combustion

Carbon dioxide does not support the burning of organic materials.

Magnesium and other metals continue to burn in carbon dioxide.


2 Mg  +  CO2  →  2MgO  +  C


Black carbon is formed.


The carbon cycle

Plants take in carbon dioxide and water producing carbohydrates and oxygen. Animals take in carbohydrates and oxygen producing carbon dioxide and water. This cycle drives life.


Copy the title – The carbon cycle

Paste the picture of the carbon cycle into your notes.

Goto the website –


Answer these questions but build them into a note.

1.     What are two processes which put carbon dioxide into the atmosphere?

2.     What name is given to the organisms that make carbohydrates?

3.     What name is given to this process?

4.     What name is given to the organisms that act on dead organisms that return the carbon in their bodies back to the atmosphere?

5.     What chemical makes shells?

6.     What do these shells eventually form?

7.     What other action puts carbon dioxide into the atmosphere?


Carbon Capture

Carbon capture is the process of capturing carbon dioxide (CO2) produced by fossil fuel power stations and storing it so it will not enter the atmosphere, normally in underground geological formations.

Goto the website


There is a lot of reading and it is quite difficult to find the information.

Answer these questions to form a note.


1.     What is carbon dioxide?

2.     What is the name for the effect for where the planet warms by the sun and then carbon dioxide prevents the heat from radiating back into space?

3.     If it weren’t for this effect what would the planet’s average temperature be?

4.     What is the name for the phenomenon which causes the temperature of the planet to slowly rise?

6.     What is the source of the majority of man-made CO2 emissions/

7.     Identify the three main steps to carbon capture and storage (CCS).

8.     There are two different types of carbon capture depending on when in the process the carbon is captured – what are the two names for these?

9.     What is the current method of transporting carbon dioxide?

10.    What are the three states that CO2 can be transported in?

11.    How many CO2 pipeline leaks were there between 1986 and 2006.

12.    What are the two places where the CO2 can be stored?

13.    What name is used for underground storage?

14.    Where can it be stored like this?

15.    How deep in the ocean would CO2 have to be released?

16.    Do you think carbon capture is a good or bad thing? Give your reasons.


CFE Outcomes

Level 4

Through exploring the carbon cycle, I can describe the processes involved in maintaining the balance of gases in the air, considering causes and implications of changes in the balance.
SCN 4-05b

National 4

The use of fuels and their environmental impact on the carbon cycle and alternative energy source including biomass

Ways to reduce carbon dioxide emissions are explored (including methods of carbon capture).