What the Teacher Will Do

What the Students Will Do

Formative Assessment

Question: What have we learned about the properties and characteristics of atoms?

 Answer: The atoms of any element are alike but are different from atoms of other elements.

1. Review properties of atoms

Question: What have we learned about molecules?

Answer: Molecules are made up of atoms. Different molecules have different properties. For example, greenhouse gases are able to absorb heat.

Question: How can molecules change?

Answer: Molecules can change by combining with other molecules, exchanging atoms with other molecules or by breaking up into separate atoms. This is called a chemical reaction.

 Question: How else can molecules change?

Answer: Molecules can change by combining with other molecules, exchanging atoms with other molecules or by breaking up into separate atoms. This is called a chemical reaction.

Question: In a chemical reaction, is matter created or destroyed?

Answer: No. When molecules react, atoms may become a part of new molecules, but there is always the same number of atoms. No new atoms are created or destroyed. This is called conservation of mass.

Question: How many of you have ever mixed vinegar and baking soda? What happened?

Answers may include: It bubbled up and spilled over the top of the container...

2. Draw on studentsÕ prior knowledge of reactive substances.

Question: Does baking soda bubble up by itself?

Answer: No.

Question: Does vinegar bubble up by itself?

Answer: No.

Question: So what do you think is happening?

 Answer: (Allow students to discuss their ideas about this.)

Say: Today weÕre going to look at oxygen and how it acts during combustion reactions

What the Teacher Will Do

What the Students Will Do

Formative Assessment

Tell students that today we will be conducting a combustion experiment.

Students listen.

What do we need for a combustion reaction to take place?

Oxygen, fuel (hydrocarbon) and an initial source of heat.

See if students remember the basic components of a combustion reaction.

What are some examples of a combustion reaction?

Burning Wood

Explosions

Car Engine

What is happening in this reaction?

When organic molecules combust the reaction products are carbon dioxide and water (as well as heat). The reaction causes more energy to be released, which initiates the next reaction. The reactions keep going through the chain of hydrocarbons.

CO₂ and water are created in combustions.

Do students remember the products of a combustion reaction?

If students do not remember, help them by drawing a reaction of a hydrocarbon and oxygen.  Ask them to consider which atoms the oxygen would react with in the hydrocarbon.

Describe the experimental procedures.  State the caution that students must take when dealing with fire.

Students listen.  Prepare for the lab by wearing goggles, tying hair back, gloves, and covered shoes.

Separate students into lab groups.

Students will get into groups.

Pass out instructions to each group.

Teacher watches students.

Begin Experiment 1

Students will first weigh the crackers and the pie pan together, and then record their masses.

Ask the students what they observed during the burning.  Do they think it will affect the weight of the cracker?

Using the matches, students will burn the cracker.

One person should hold a paper plate (with tongs) over the cracker to catch the water vapor.

Students should recognize that the vapors that they see coming from the burning cracker contributed the crackerÕs original weight.

Students weigh the cracker and pie pan.?

Begin Experiment 2

Weigh the empty pie pan and record the mass.

Place a pad of the steel wool (approximately 3 in x 3 in) in the pan and record the weight of the pan and pad.

Light the burner and adjust it to obtain a blue (hot) flame

Ask the students what they observed during the burning of the steel wool?

Students should definitely be wearing lab aprons, gloves, and goggles during this portion of the lab.

Hold the steel wool with the tongs and place it in the flame for several minutes. Rotate the pad so that all parts are exposed to the flame. After all of the pad has a dull gray appearance, turn off the burner. Place the steel wool in the pie pan, sweeping any "popped" pieces of the steel wool into the pie pan as well.

Weigh the pan and steel wool and record the mass.