Unit Four: Chemical Reactions and Stoichiometry

Lesson 3: Types of Chemical Reactions

• Comptencies
• Starter Activities
• Main Activites

Competencies

• List the four types of chemical reactions
• Conduct experimental activities on the types of chemical reactions
• Identify the type of a chemical reaction
• Write chemical equations for each type chemical reaction.

Materials:

Test-tubes, Burners, Tongs, Test-tube holders, Medicine droppers

Note for the teacher

Here are some selected chemical reactions for demonstration; it is hoped that these simple reactions are used to stabilize students understanding of chemical reaction and the association of theoretical knowledge to practical activities. As usual, you can provide materials for groups if they are available or demonstrate yourself by participating students in the process. The lesson can be provided at the end of the types of chemical reaction to sum up the contents.

Starter activity (5minutes)

As a starter activity, types of chemical reactions can be revised. They may be asked: how many types of reactions are there, their names, examples and special features of each type of reactions.
Here students are expected to list combination (synthesis), decomposition, single displacement and double displacement reactions, write their general equations and give specific examples of each type of reaction.

Evaluation

Let the students write examples of types of reactions on the chalk board.

Main activity (26minutes)

 Demonstrate the following types of chemical reactions. Follow the directions for each reaction carefully. After conducting each experiment, record your observations. Identify the types of reactions, the reactants and products and then write the balanced chemical equation for the reactions.

YOU MUST WEAR SAFETY GOGGLES DURING THIS LAB ACTIVITY!
Activity1.

• Using a pipet, place about 1 mL (one pipet-full) of ethanol (C2H6O) on a watch glass.
• Using a safety lighter or matches ignite the ethanol and allow it to burn completely.
•  Do not touch the hot watch glass!

Activity 2:

• Obtain a small piece of copper wire or a few strands of copper wool.
• Using tongs, hold the copper in the hottest part of a Bunsen burner flame and heat for approximately 1 minute. (Have someone tilt the burner as you heat so that copper doesn’t enter the burner).
• Allow the product to cool and then dispose of it in the trash.

Activity 3:

• Pour approximately 25 mL of hydrogen peroxide (H2O2) into a 250 mL beaker.
• Add one of the following  A small chunk of potato or  A spoonful of potato slurry or A very small spoonful of active dry yeast
• Observe the reaction for approximately one minute. When finished, pour the solution down the drain with plenty of water.

The potato and yeast are not directly involved in this chemical reaction. What is their purpose?
Activity 4:

• Obtain a small piece of iron wire. If the wire is rusty, clean it thoroughly with a piece of sandpaper until it is shiny. Then, coil the end of the wire around a pen or pencil.
• Pour approximately 20 mL of copper (II) sulfate solution into a small beaker.
• Dip the coiled end of the wire into the copper solution for about 10-20 seconds and then remove.

Activity 5:

• Combine one pipet-full of 0.5 M calcium chloride and one pipet-full of 0.5 M sodium carbonate to a test tube.
• When finished, dispose of the contents of the test tube down the drain and rinse thoroughly.

Activity 6:

• Add approximately 150 mL of tap water to a 250 mL beaker.
• Add 10-15 drops of the acid-base indicator of your choice (record this in your observations).
• Add 5-10 drops of sulfuric acid to the water. Note the color of the indicator.
• Continue to add drops of sodium hydroxide until you get a permanent color change. Again, note the color of the indicator.
• When finished, pour the contents of the beaker down the drain.
• If time permits, you may repeat this experiment with another indicator.

Let the students report their observations and conclusions as follows. One example is given for each type of task.

Generalization

Let the students discuss and write down the general features of the chemical reactions based on their observations. They may be asked a question as: ‘How do you describe each type of chemical reaction?
After students discuss and give their own description of the reactions, make sure that they included the following information in their statements.

Combustion reaction is rapid chemical reaction of two or more substances with a characteristic liberation of heat and light; it is commonly called burning. The burning of a fuel (e.g., wood, coal, oil, or natural gas) in air is a familiar example of combustion

Decomposition reaction is separation of a substance into two or more substances that may differ from each other and from the original substance. The separation may be caused by heat, light, catalyst or electric energy.

A combination reaction or a synthesis reaction is a reaction in which two or more reactants are chemically bonded together to produce a single product. When two or more substances combine to form a single product, it is known as a combination reaction. Many elements react with one another in this fashion to form compounds.

A single-displacement reaction, also called single-replacement reaction, is a type of oxidation-reduction chemical reaction when an element or ion moves out of one compound and is replaced by another.
Double displacement reaction is the reaction in which two compounds react by an exchange of ions to form two new compounds. A double displacement reaction usually occurs in solution and one of the products being insoluble or precipitates.

Evaluation  

Students may be asked to define each type of chemical reaction and give example using chemical equation.

Concluding activity

You may different types of activities to assist students conclude their lesson on types of chemical reactions. Some examples are given below.

Activity 1

Match the types of reactions under column A with their descriptions under column B

Activity 2

Identify the type of reaction shown in each of the following chemical equations:

a. KClO3(s) → 2KCl(s) + 3O2(g)
b. AgNO3(aq) + KCl(aq) →  AgCl(s) + KNO3(aq)
c. 2 H2(g) + O2(g) → 2 H2O(g)
d. HBr(g) + Cl2(g) →  HCl(g) + Br2(g)