Demonstration and Practical - Decomposition Reactions.
Aim: To observe and describe decomposition reactions.
Introduction
Decomposition is the creaking down on chemicals into its components. Describe the
demonstration from the teacher using the Hoffman Voltameter
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How do you know which side is Oxygen and which is Hydrogen?
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The general word equation for a decomposition reaction is
Compound → Element 1 + Element 2
Record the specific word equation for the demonstration
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Equipment:
Side arm test tube
Matches
Teaspoon of copper carbonate (CuCO3)
Test tube holder
Boiling tube
Retort stand
Method:
1. Place a 1/2 teaspoon of copper carbonate into a test tube
2. Stopper the test tube
3. Use the retort stand to clamp the test tube
4. Direct the tubing into a boiling tube with 2-3cm of lime water
5. Using the test tube peg to hold the boiling tube in place
6. Light the Bunsen burner and heat the test tube with copper carbonate
7. Remove the tubing from the boiling tube before (or as soon as) the heating is stopped
8. Record your observations
Results:
Observations _______________________________________________________________________________
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1. Write a specific word equation for the decomposition reaction.
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2. Write a balanced symbol equation for the reaction.
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Conclusion:
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Decomposition reactions practice
Hydrogen peroxide (H2O2) is a widely used
disinfectant for minor cuts and scrapes. You may
have a bottle of hydrogen peroxide like the one
pictured here in your medicine cabinet at home. Did
you ever notice that hydrogen peroxide is always
kept in a dark brown bottle like this one? Do you
know why? The reason is that hydrogen peroxide
needs to be protected from light. If it isn’t, it will
gradually break down to water and oxygen. This is a
decomposition reaction.
Write a word equation for the above reaction:
What Is a Decomposition Reaction?
A _________________ reaction occurs when ______ _____________ breaks down into ______
or _____________ products. It can be represented by the ______________ equation:
____ → __ + __
In this equation, AB represents the ____________ that ___________ the reaction, and A and B
represent the ____________ of the reaction. The ___________ shows the _____________ in
which the reaction occurs.
AB
reactant
one
arrow
begins
products
B
more
reactant
decomposition
two
direction
A
general
Q: What is the chemical equation for the decomposition of hydrogen peroxide (H2O2) to water
(H2O) and oxygen (O2)?
A:
Other Examples of Decomposition Reactions
Two more examples of decomposition reactions are described below.
You can see additional examples at this URL: http://www.youtube.com/watch?v=dxlWtsFinTM
• Carbonic acid (H2CO3) is an ingredient in soft drinks. A decomposition reaction takes place
when carbonic acid breaks down to produce water (H2O) and carbon dioxide (CO2). This occurs
when you open a can of soft drink and some of the carbon dioxide fizzes out. The equation for
this reaction is:
Another decomposition reaction occurs when water (H2O) breaks down to produce hydrogen
(H2) and oxygen (O2) gases (see Figure 1.1). This happens when an electric current passes
through the water, as illustrated below. The equation for this reaction is:
Summary
• A decomposition reaction occurs when one reactant breaks down into two or more products.
This can be represented by the general equation: AB → A + B.
• Examples of decomposition reactions include the breakdown of hydrogen peroxide to water
and oxygen, and the breakdown of water to hydrogen and oxygen.
FIGURE 1.1 Decomposition of water.
Part 2
A synthesis reaction occurs when two or more reactants combine to form a single product. This
type of reaction is represented by the general equation: A + B → AB. An example of a synthesis
reaction is the combination of sodium (Na) and chlorine (Cl) to produce sodium chloride (NaCl).
1. Why are decomposition reactions the opposite of synthesis reactions?
2. What are the expected products of the decomposition of hydrogen chloride (HCl)?
1. What is a decomposition reaction?
2. What is the general equation for a decomposition reaction?
3. Describe the decomposition of hydrogen peroxide and write a
balanced chemical equation for this reaction.
4. Which of the following chemical equations represents a
decomposition reaction?
a. H2SO3 → H2O + SO2
b. 2Na + Cl2 → 2NaCl
c. 2K + 2H2O → 2KOH + H2
d. NaCl + AgF → NaF + AgCl
Part 3: Decomposition Reactions
In decomposition reactions, one compound will break down into two or more parts. Ensure
both word and balanced symbol equations are completed for each of the following. The first
one has been completed for you.
1. barium carbonate → barium oxide + carbon dioxide
BaCO3 → BaO + CO2
2. magnesium carbonate →
3. potassium carbonate →
4. zinc hydroxide → zinc oxide + water
5. Iron(II) hydroxide →
Fe(OH)2 →
6. nickel(II) chlorate → nickel(II) chloride + oxygen
Ni(ClO3)2 →
7. sodium chlorate →
2NaClO3 →
8. potassium chlorate →
2KClO3→
9. sulfuric acid → water + sulfur trioxide
H2SO4→
10. carbonic acid → water + carbon dioxide
H2CO3 →
11. aluminium oxide → aluminium + oxygen
2Al2O3→
12. silver oxide →
2Ag2O→