Download large scale pop test

TEACHERS NOTES
LARGE SCALE POP TEST
Recommended year levels: 11-12
OBJECTIVES
1. To observe the production of hydrogen gas
2. To demonstrate some properties of hydrogen gas.
BACKGROUND INFORMATION
Hydrogen is a very light gas that was once used to inflate
air ships. It is also odourless, colourless and highly
flammable. In the presence of oxygen and a small spark,
it readily forms water in an explosive reaction.
(2H2 + O2 Æ 2H2O)
For this reason the Hindenberg disaster occurred and
hydrogen was replaced with helium for inflation
applications.
Hydrogen is the most abundant element in the universe – 93% of all atoms in the universe are
hydrogen atoms. It is also the most abundant element on the sun. Although it constitutes only
0.14% of the elements in the Earth’s crust, water – a compound of oxygen and hydrogen – covers
about two thirds of the Earth’s surface.
The reaction to produce Hydrogen from sodium hydroxide (NaOH) and aluminium is as follows:
• Aluminium is highly reactive and so reacts with oxygen to form a protective coating of aluminium
oxide. The alfoil that is placed into solution already has a coating of aluminium oxide (Al2O3).
This is dissolved by the sodium hydroxide.
Al2O3 + 2NaOH + 3H2O Æ 2Na+ + 2 [Al(OH)4]• The exposed aluminium surface can then react with water to form hydrogen.
2 Al + 6 H2O Æ 2 Al(OH)3 + 3H2
• This surface layer of aluminium hydroxide then is dissolved by the sodium hydroxide to expose
another surface of aluminium which can react with H2O following the previous equation.
Al(OH)3 + NaOH Æ Na+ + [Al(OH)4]-
MATERIALS
•
•
•
•
•
•
•
•
Small bucket or beaker (e.g. ice cream bucket)
Sodium hydroxide 20mL 1M
Aluminium foil (30cm x 10cm)
Balloon
200mL conical flask
2 x 1 metre stick (ruler or dowel)
Matches
Tape
PROCEDURE
1. Rip the aluminium foil into about 10 smaller pieces. Twist each piece and put into the conical
flask.
2. About ¼ fill the ice cream bucket with water. Place the conical flask in the water in the bucket.
3. Add the sodium hydroxide to the conical flask. Quickly cover with a balloon.
4. When the reaction is complete carefully pinch the end of the balloon and separate from the
flask. Tie off the end of the balloon.
5. Use sticky tape to attach a match to the end of a metre stick.
© Harper, A., and Nickels, K. 2008. Queensland University of Technology.
6. Attach the balloon to the end of the other metre stick.
7. Ensure you are standing outside, at least 2m from any flammable objects. One person will hold
out the balloon away from their body, the other person will hold out the match to the balloon.
Ensure that any other people are at least 2m from where the balloon and match will meet.
8. Light a match and use it to light the match attached to the metre ruler. Hold out the match to
meet the balloon.
QUESTIONS
1. Describe your observations when the aluminium and sodium hydroxide were mixed. There was
bubbling, heat produced and the balloon expanded.
2. Describe your observations when the match was held to the balloon. There was a release of
heat, light and sound energy.
3. What were the reactants and what were the products? The reactants were aluminium, sodium
hydroxide and water. One of the products was hydrogen gas. The other product was an ionic
compound of sodium aluminium and hydroxide ions.
4. What would be a highly inappropriate or dangerous application of using hydrogen gas? An
airship where the gas is used to float it but there is lots of heat available to spark a fire.
EXTENSION
Try filling other balloons with other gases (e.g. nitrogen or carbon dioxide). Compare what happens
when the balloons are popped with a match.
Investigate reaction rates by using different concentrations of sodium hydroxide?
Investigate the effects of using different quantities of aluminium foil on the size of the balloon.
REAL WORLD APPLICATIONS
Chemical production – hydrogen is used to react with the sulfur in petroleum so that the sulfur
does not form sulfur dioxide when the fuel is burnt. It is also used in the production of Ammonia for
fertilizers and explosives through the Haber process.
Fuel cells – hydrogen can be used in a fuel cell to power vehicles such as buses and cars. When
used hydrogen is used in a fuel cell the only by-product is water so it is very environmentally
friendly.
Glass making – flat glass is made from floating molten glass on molten tin. Hydrogen is used to
remove oxygen and make sure that there is no rust on the surface of the tin.
Space exploration – liquid hydrogen powered the space shuttle launch. It carries more energy
than petrol and is lighter. Although it takes up a larger volume the other savings outweigh this.
CURRICULUM CONCEPTS ADDRESSED
R2.1—All chemical reactions involve energy transformations.
R2.2—The spontaneous directions of chemical reactions are towards lower energy and greater
randomness.
RESOURCES USED TO DEVELOP THIS ACTIVITY
1.
2.
3.
BOC Gases. n.d. http://www.boc.ebcnet.co.uk/nitrogen/index.html (accessed 6 November
2008).
O’Brien, M. 2008.
http://www.sciencedemonstrations.com/demonstrations/hydrogen_balloon.pdf
(accessed 8 November 2008).
© Harper, A., and Nickels, K. 2008. Queensland University of Technology.