Lesson 10- Reactants & Products

Lesson 10- Reactants & Products

Objective 2	Describe some chemical reactions.
Objective 2.2	Recognize that a chemical reaction involves reactants and products.
Objective 2.3	Recognize those characteristics which indicate that a chemical reaction has taken place.
Objective 2.4	Investigate the effect of temperature on the rate of a chemical reaction.

Instructional Strategies

Structured overview, problem solving, experiment, research, assigned questions

Students read the notes on Reactants and Products.

Students work through the word equations sheet identifying reactants and products. The teacher copy is available as an answer key.

A video demonstration of this lab is available on the student page. But, if at all possible, demonstrate this lab to your students or have them complete it. It is fun and definitely will get their attention!

LAB 10: WHAT DO ELEPHANTS BRUSH THEIR TEETH WITH? ELEPHANT TOOTHPASTE!
(Write out the lab).

PROBLEM: What do you think will occur when soap is added to the hydrogen peroxide and the sodium iodide is added to the solution?

HYPOTHESIS: How do you think it is going to turn out? Use the facts you already know to come up with a guess that might really make sense.

MATERIALS:

50 mL to 100 mL 30% hydrogen peroxide
10 mL saturated potassium iodide solution
10 mL liquid soap or dishwashing liquid
food coloring
2 plastic garbage bags (large size)
a graduated cylinder (500 mL or larger, glass is preferable to plastic)
a pair of scissors
a pair of safety goggles
a pair of rubber gloves

PROCEDURE:

Put on the safety goggles and gloves.
Use the scissors to cut one of the garbage bags down one side and across the bottom. Open the bag and spread it over the demonstration area. Save the remaining bag for cleanup.
Place the graduated cylinder on the open bag.
Fill the cylinder to about ¼ full with 30% hydrogen peroxide.
Add from 5 mL to 10 mL liquid soap or dishwashing liquid.
Sprinkle some food coloring on the inside wall of the cylinder.
Add 10 mL saturated potassium iodide solution.
STAND BACK! In a few seconds a column of foam will rise out of the cylinder and overflow onto the open bag.

ANALYSIS:

Describe what you observed.
Did your observations match you predictions? How are they similar? different?

CONCLUSION: What actually occurred during this experiment?

This activity demonstrates the decomposition of hydrogen peroxide catalyzed by potassium iodide. The rapid production of oxygen causes the mixture to foam, rise, and overflow the cylinder. The iodide is a catalyst because it speeds up the reaction of the hydrogen peroxide decomposing. This is an exothermic reaction, and the energy released is in the form of heat. You will notice steam rising from the cylinder, as well, it is warm to the touch.

You can reveal the presence of oxygen in the foam by performing a glowing splint test. Place a glowing splint in the foam and it will relight, indicating that oxygen is present. Do not drop the splint into the cylinder. The brown color of the foam indicates that iodine is present. Iodine can stain clothing and skin, so avoid contact with the foam.

EXTENSION:

Explain the difference between endothermic and exothermic reactions.

Do research on a chemical change. In your research, try to determine the reactants and products of that change. Include in your write-up other interesting information you may find. You will share your research with your classmates to see whether they can write a word equation for your chemical change.

Here are some possibilities:

What is the chemical change involved in obtaining iron from iron ore? Do an internet search for steel mill mines and see if you can find information to help you with this question.
Plaster of Paris is made from gypsum. What chemical change is involved?
What can you learn about the reactants and products in making cement?
Your flashlight dry cell uses a chemical change to produce electricity. What are some reactants and products in this change?
Talk to a photographer to learn about the chemical changes involved in taking and developing photographs.
The formation of limestone (calcium carbonate) caves. What is the chemical reaction that causes the caves to form?
Identify the chemical reaction that occurs in photosynthesis.

Remind students to use the proper safety procedures and lab format while completing the lab.

LAB 11: HOT OR COLD?
(Write out the lab).

PROBLEM: How does temperature affect reaction rate?

HYPOTHESIS: How do you think it is going to turn out? Use the facts you already know to come up with a guess that might really make sense.

MATERIALS:

4 Al ka-Seltzer tablets
4 large glasses or beakers (250 mL each or larger)
ice
hot water (from a kettle)
thermometer
watch or timer

PROCEDURE:

Prepare a table where you can record your results for each of the four beakers. The two columns should be labeled"Temperature" and "Time."
Fill one glass with ice and water, and the others with cool, hot and very hot water.
Use the thermometer and record the temperature of the water in each of the four glasses.
Before the water has a chance to cool, drop one tablet into each of the four glasses at the same time. Record the time taken to complete the reaction in each glass.

ANALYSIS:

What happened to the Al ka-Seltzer tablets in water?
What evidence do you have that a chemical reaction occurred?
How did temperature affect the rate of the reaction?
Make a graph of time vs. temperature. Plot your four points on the graph and join them with a smooth curve. (Excel could be used to create this graph). Make sure you title your graph.
Use the graph you created to predict the amount of time that would be necessary for a similar reaction at 40 degrees C and at 60 degrees C.
Think about the following theory, "Particles in matter are constantly moving and they move more quickly at higher temperatures." Use this theory to explain your results.

CONCLUSION: What actually occurred during this experiment?

Lab Report Evaluation Form