Investigating Ethanol Burning!
Part 1: Make predictions that will help you answer the three questions.
Predictions about mass changes: Predictions about changes in BTB:
What will gain mass? Do you think that BTB will change color if it is in a closed container with burning ethanol?
What will lose mass?
YES NO
What color change do you predict?
The Carbon Question: What do you think is happening to molecules that have carbon atoms in them?
The Movement Question: Draw your ideas about how atoms are moving on the picture below.
Where are atoms moving from?
Where are atoms going to?
The Energy Question: How do you think that energy is changing from one form to another?
Part 2 - Lab: What Happens When Ethanol Burns?
Purpose: To conduct an investigation of ethanol burning to determine the transformation of matter and energy that takes place in this chemical change.
Materials

A balance that weighs materials accurately to 0.01 grams

An air-tight (or mostly air-tight) container

Bromothymol blue (BTB) solution to detect CO
2
in the air inside the container

Cobalt blue paper that detects H
2
O in the air inside the container

Ethanol that you can burn in a shallow glass watch glass
Procedure
1. Add 1 dropper-full (1 mL) of ethanol to a watch glass
2. Turn on a digital scale so that it reads “0.00” g. Place the watch glass with ethanol on the scale.
Record the mass of ethanol in the data table below.
3. Place 5 drops of BTB on another Watch glass. Fill in your observation of the color of the BTB in the data table below.
4. Place a piece of Cobalt Blue paper next to the watch classes. Record the initial color

5. Place the Watch glass with BTB next to the Watch glass with ethanol so that the large 4L inverted container lined with aluminum will be able to fit on top of the two watch glasses.
6. Light the ethanol with the lighter and then immediately put the large 4L container lined with aluminum foil on top the Watch glass with burning ethanol and the Watch glass of BTB. The flame will go out quickly inside the container.
7. Wait 5 minutes before taking the lid off the container. Observe and record changes in the color of the BTB in the data table.
8. Place the Watch glass with ethanol on the digital scale and record the mass of the ethanol in the data table.
9. Record the color of the BTB after the experiment in the data table.
10. Calculate the change in mass for ethanol and record in data table.
11. Record your results on the class data table.
Group Data
Measurements Before Burning
Mass of Watch glass with ethanol
Mass: _______________ grams
Measurements After Burning
Mass of Watch glass with ethanol
Mass: _______________ grams
Change in mass: ____________ grams
Changes in color of BTB
Color: _______________________
Change in color? Yes / No
Color of BTB
Color of BTB:
________________________
Color of Cobalt Chloride Paper
Color of paper:
________________________
Class Data
Control
(no burning)
Class
Data
Average
Change in
Mass (g)
Final Color
BTB
Final Cobalt
Chloride
Changes in color of Cobalt Chloride Paper
Color: _______________________
Change in color? Yes / No

Part 3: Using molecular models to show the chemical change.
Ethanol is a good fuel because it has a lot of chemical potential energy stored in its bonds. Energy is stored in its high-energy bonds: C-C and C-H bonds. When ethanol burns, it reacts with oxygen in the air to produce carbon dioxide and water. Since carbon dioxide and water have only low-energy bonds (C-O and H-O), the chemical energy is released as heat and light.
1. Make models of an ethanol molecule (C
2
H
5
OH) and three oxygen molecules (O
2
, with a double bond). .
2. Copy the Chemical Change Diagram onto your whiteboard:
Chemical
Change
3. Put the ethanol and oxygen molecules on the reactant side of the Chemical Change Diagram on your whiteboard.
4. Use twisty ties to represent chemical energy. Put a twisty tie around each high-energy bond (C-C and C-H bonds) in the ethanol molecule. Put t he “Chemical Energy” card under the ethanol molecule to label the energy in the C-C and C-H bonds. Note how many energy units (twisty ties) there are in the ethanol.
5. Use the table below to record information about the atoms and energy for the reactant side of the equation:
Matter (list number of atoms) Energy
Carbon Oxygen Hydrogen How many twisty ties? What forms of energy?
Reactants
Ethanol
Oxygen
Products
Carbon
Dioxide
Water
Totals
6. Show how the atoms of the reactant molecules can recombine into product molecules —carbon dioxide and water —and show how chemical energy is released when this happens. Take the ethanol and some of the oxygen molecules apart and recombine them into carbon dioxide (CO
2
) and water (H
2
O) molecules. Put these molecules on the product side of the whiteboard. a) How many oxygen molecules reacted with one ethanol molecule? _____ b) How many carbon dioxide molecules were produced? _____ c) How many water molecules were produced? _____

7. Energy lasts forever, so move the twisty ties to the product side of the Chemical Change Diagram whiteboard. Carbon dioxide and water have low-energy bonds (C-O and H-O), so what forms does the chemical energy change into? Put the correct energy cards under the twisty ties.
8. Atoms last forever!! Check yourself: Did your number and type of atoms stay the same at the beginning and end of the chemical change? _____________________________
9. Energy lasts forever! Write the type of energy for reactants and products in the energy column above.
10. Write a balanced chemical equation using the molecular formulas and the yield sign (  ):
11. Revise your answers to the “What Happens when Ethanol Burns?” chart in your journal.