Chemical Reactions Un-Notes

Ask students, "What are you going to learn today?".  Students should respond by saying that they will be answering the Essential Question, "How do particles combine into new substances? And, what evidence can show how the physical and chemical properties of the substances change?"  This EQ is posted on my board and on the student's Chemistry Unit Plan. 

Explain to students that this lesson represents the first lesson that students work with Skill 5 of the Chemistry Unit Plan, "I can provide evidence to show if a reaction is a chemical or physical change."  Have the students turn to their unit plans and silently read the skill.  After reading the skill have the students rank their current level of mastery on a scale of 1 to 4 (4 being mastery).  

In my classroom, students frequently self-assess their level of understanding on each skill in the unit as we go.  As you can see from the image below, this student ranks herself as a "2" to start this lesson.  As we work more on this skill in the upcoming lessons, the student will re-assess and update this score.

Explain to the students that scientists not only use evidence to support their claims, but they also search for patterns in their evidence in order to predict phenomena. Scientists analyze and interpret data to explain phenomena they see in the world. Let students know that in today's lesson they will need to use their observation skills as they watch multiple reactions to collect data that they can use to predict if reactions are chemical or physical changes.   

For a look at all the lessons that have led my students to this point and where we go from here check out the lessons in these units:

Physical Properties:  Molecular Arrangement and Phase Changes:  Focuses on Skills 1 - 4 of the Chemistry Unit Plan

This unit is designed to answer the Essential Question, "How do particles combine into new substances? What evidence can show how the physical and chemical properties of the substances change?".

It particularly focuses on types of matter, physical properties, phase changes, and factors that affect physical properties. This unit's purpose is so much more than just the content, however. It's focus is scientific literacy. It stresses group discussion, discourse and utilizing text references when engaging in argument. Students utilize reading, writing, and speaking strategies in order to develop scientific literacy. It's scientific literacy immersion!

Chemical Properties and Reactions:  Focuses on Skills 4 - 6 of the Chemistry Unit Plan.

This unit is also designed to answer the Essential Question, "How do particles combine into new substances?  What evidence can show how the physical and chemical properties of the substances change?".  This unit focuses on chemical properties and chemical reactions.  Students analyze evidence and property changes that allow them to distinguish between chemical and physical reactions.  In addition, students investigate the Law of Conservation of Mass as they look at how bonds are broken and formed in chemical reactions.  This unit is full of hands on labs and station rotations that will engage any middle school student in chemistry!

Provide students with the Chemical Reactions Un-Notes Sheet.  Explain that during each reaction, they need to write down as many observations that they can see during the reactions.  As we are trying to determine evidence that will determine if a reaction is chemical or physical, it is important for students to especially note any changes to the properties of the substances involved that they see occurring.  

It is also important for students to be aware that the chemical being used in these reactions have safety and health hazards.  Students must wear goggles and may not touch any of the products formed during the reactions.  It is important for you as a teacher to read all of the safety and health hazards for each chemical used in the demonstrations to ensure that you and the students are safe during these reactions.

In my classroom, on the first day of a new unit or skill, I have students participate in demonstrations or labs in which the students develop their own understanding instead of taking traditional notes.  Instead of me telling students the signs of a chemical change, they can discover this for themselves.  Students call these "un-notes" because that are so different than the typical notes they are used to taking.

Demonstration #1:  The Iodine Clock Reaction

Materials:

¼ and ½ tsp measuring spoons

3 beakers – 500 ml 

Stirring rods or spoons

Mixture of ¼ tsp sodium sulfite and ¼ tsp citric acid

Procedure:

1.  Pour ¾ cup water into 1st beaker.

2.  Stir in 1 starch pellet until it (sort of) dissolves (it won’t entirely).

3.  Stir in ½ tsp sodium sulfite/citric acid mixture until dissolves.

4.  In 2nd beaker, pour in ¾ cup water.

5.  In 2nd beaker, stir in ¼ tsp sodium iodate until dissolves.

6.  Pour beaker 1 into beaker 2.

7.  Pour mixture back into beaker 1.

8.  Pour mixture into beaker 3.

This one happens "all of a sudden".  Let students know that even if it looks like nothing is happening, that they shouldn't take their eyes off it or they will miss it!  After the reaction has finished, provide students time to write down their observations.

Demonstration #1:  Rocket Engine

Materials:

Test tube

Ring Stand

Bunsen burner

Long eye dropper

Matches

Potassium Chlorate

Manganese Dioxide

Glycerine

Procedure:

1.  Attach a test tube at an angle on a ring stand over a Bunsen burner.  Make sure that the opening of the test tube is not pointed at students.

2.  Place a small amount of Potassium Chlorate (about the tip of a scapula) in the bottom of the test tube.

3.  Place a small amount of Manganese Dioxide (about the tip of a scapula) on top of the Potassium Chlorate.

4. Using a long eye dropper, place a few drops of glycerin on top of the powders.

5.  Light the Bunsen burner.  (The burner is only supplying heat, lower the flame so that it is not "engulfing" the bottom of the test tube.)

This one takes a minute to develop.  When the smoke starts, it's almost ready to react!  After the reaction has finished, provide students time to write down their observations.

Demonstration #3:  Elephant's Toothpaste

Materials:

2 100 mL beakers

30% Hydrogen Peroxide

Saturated solution of Potassium Iodide

Gloves

Dawn dish detergent

Food coloring

Wooden Skewers

Matches

Procedure:

1.  Wearing gloves, pour 80 mL of the 30% Hydrogen Peroxide into a large graduated cylinder (you can use a 2 Liter bottle as well).

2.  Squeeze about 30 mL of Dawn dish detergent (the amount does not need to be exact).

3.  Swirl the two around in the bottom of the container.

4.  Drip two different colors of food coloring in the "corners" of the cylinder.  This is what will make it look like toothpaste.

5.  Pour in 40 mL of the saturated Potassium Iodide solution.

6.  Step back!

7.  Once the reaction is complete, light the end of a wooden skewer and then blow it out so that there are red embers left at the end.  Slowly lower the hot tip into the bubbles.  The skewer will reignite!  

After the reaction has finished, provide students time to write down their observations. 

Provide students with time to complete the Chemical Reactions Un-Notes Page.  This page can be challenging.  Encourage group dialogue when completing it.  Analyzing data to identify patterns is a skill that most middle school students have not yet mastered.  Group discussion will be important to help students recognize the patterns in the data.