Chemical Reactions Labs – Synthesis & Decomposition Reactions
REACTION 1: LAB INSTRUCTIONS
Safety:
 Wear safety goggles at all times.
 Clean up the lab table and surrounding area as instructed by your teacher.
Materials:




250 mL beaker
50 mL of 3% hydrogen peroxide solution
Pinch of yeast
Wire gauze pads
Directions:
1. Add about 50mL of 3% hydrogen peroxide to the beaker.
2. Add a pinch (very small amount) of yeast to the beaker and cover the beaker with a wire
gauze pad immediately.
3. Allow the reaction to proceed until it has slowed considerable (about 3 minutes).
4. Record your observations.
5. Keep your set up for reaction 2.
Supporting Video Examples:

http://www.youtube.com/watch?v=8zlAdj-c0m8
Chemical Reactions Labs – Synthesis & Decomposition Reactions
REACTION 2: LAB INSTRUCTIONS
Safety:
 Wear safety goggles at all times.
 Clean up the lab table and surrounding area as instructed by your teacher.
Materials:





Set up from Reaction 1 (do not dispose of this yet)
Steel wool (3 cm x 3 cm)
Tongs
Striker
Thermal Gloves
Directions:
1. Get a small piece of steel wool and fluff it up (should be able to see the little fibres).
2. One group member will hold the steel wool with the tongs (with thermal gloves on),
while the other partner uses the striker to produce a spark that falls onto the steel wool.
3. As soon as the spark begins to spread through the steel wool, slide the wire gauze pad to
one side, just enough to insert the steel wool.
4. Plunge the burning steel wool into the oxygen gas, and slide the wire gauze pad back
over to cover most of the beaker.
5. Hold the steel wool in the middle of the beaker, about 5 cm above the liquid (do not
touch the liquid because it will extinguish the fire).
6. Allow everything to cool. Clean up the glassware and your work area.
7. Dispose of all waste materials into the garbage.
8. Complete your worksheets for both reactions.
Supporting videos:

http://www.youtube.com/watch?v=cJFGr2R3V44
Name: ___________________________________
Date: ____________________
Chemical Reactions Lab – What type of reaction is it?
REACTION 1:
Hydrogen peroxide is a very unstable compound and breaks down into its products, water (H2O)
and oxygen gas (O2). When exposed to light, the process occurs more rapidly. Therefore,
hydrogen peroxide must be stored in dark brown opaque bottles to help prevent the hydrogen
peroxide from breaking down. In this reaction, yeast is added to Hydrogen peroxide (H2O2) to
help speed up the reaction. Yeast is not used up in the reaction; it simply helps the hydrogen
peroxide form the products faster than it would when left alone. Do not include yeast on the
reactant or product side. When writing the formula, place yeast above the arrow.
Answer the Following Questions:
1. What do you observe during the reaction when yeast is added to hydrogen peroxide?
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
2. Is this a physical or chemical reaction? How do you know?
__________________________________________________________
__________________________________________________________
__________________________________________________________
3. What type of reaction is this (synthesis or decomposition)? How do you know?
__________________________________________________________
__________________________________________________________
__________________________________________________________
4. Write a chemical word equation for the reaction.
______________  ____________ + ____________
5. Write the skeletal equations for the reaction.
__________ (_)  ________ (_) + ________ (_)
6. Write a balanced chemical equation for the reaction.
__________ (_)  ________ (_) + ________ (_)
Name: ___________________________________
Date: ____________________
Chemical Reactions Lab – What type of reaction is it?
REACTION 2:
In reaction two, you take steel wool and give it some heat with a striker. You place the steel
wool in the beaker from Reaction 1. When the iron reacts with the oxygen, the substance iron
oxide (Fe3O4) is created. In this reaction, heat is used to help speed up the process. Do not
include heat on the reactant or product side. When writing the formula, place heat above the
arrow.
Answer the Following Questions:
1. What do you observe during the reaction when the steel wool is placed inside the
beaker? What does the remaining material look like?
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
2. Is this a physical or chemical reaction? How do you know?
__________________________________________________________
__________________________________________________________
__________________________________________________________
3. What type of reaction is this (synthesis or decomposition)? How do you know?
__________________________________________________________
__________________________________________________________
__________________________________________________________
4. Write a chemical word equation for the reaction.
______________ + ____________  ____________
5. Write the skeletal equations for the reaction.
__________ (_)+ ________ (_)  ________ (_)
6. Write a balanced chemical equation for the reaction.
__________ (_) + ________ (_)  ________ (_)
Name: ___________________________________
Date: ____________________
Chemical Reactions Lab – What type of reaction is it?
REACTION 1: ANSWERS
1. What do you observe during the reaction when yeast is added to hydrogen peroxide?
When yeast is added to the hydrogen peroxide, it starts to foam up and bubble. The beaker
begins to fill with a gas and the walls of the beaker look as if someone has blown hot air on
them.
2. Is this a physical or chemical reaction? How do you know?
Chemical reaction  a gas has been formed (oxygen gas O2).
3. What type of reaction is this (synthesis or decomposition)? How do you know?
Decomposition reaction because the hydrogen peroxide is breaking down into water and oxygen
gas.
4. Write a chemical word equation for the reaction.
yeast
Hydrogen peroxide  water + oxygen gas
5. Write the skeletal equations for the reaction.
H2O2 (l)  H2O (l) + O2 (g)
6. Write a balanced chemical equation for the reaction.
2H2O2 (l)  2H2O (l) + O2 (g)
Name: ___________________________________
Date: ____________________
Chemical Reactions Lab – What type of reaction is it?
REACTION 2: ANSWERS
1. What do you observe during the reaction when the steel wool is placed inside the
beaker? What does the remaining material look like?
When the steel wool is placed inside the beaker, sparks will fly and the steel wool will burn. The
remaining material will be a blue-black crumbly material, which is the new substance.
2. Is this a physical or chemical reaction? How do you know?
Chemical reaction  oxidization is occurring and a new substance is formed, which cannot be
converted back into its component parts.
3. What type of reaction is this (synthesis or decomposition)? How do you know?
Synthesis reaction because the iron is reacting with the oxygen to form iron oxide, which is a
new compound.
4. Write a chemical word equation for the reaction.
heat
Iron (steel wool) + Oxygen  Iron oxide
5. Write the skeletal equations for the reaction.
Fe (s) + O2 (g)  Fe3O4 (s)
6. Write a balanced chemical equation for the reaction.
3Fe (s) + 2O2 (g)  Fe3O4 (s)