Types of Reactions Demo Day

10 teachers like this lesson
Print Lesson

Objective

TSWBAT identify five different types of chemical based on how reactants form products.

Big Idea

Students love demos and at the same time they can reinforce the concept of chemical reactions and conservation of mass .

NGSS Standard Alignment

Performance Expectation (PE)/Disciplinary Core Idea (DCI)

This lesson is aligned with HS-PS1-7, the uses of mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction; and DCI-PS1.B, the fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.  Student were introduced the previous day to the 5 different chemical reactions that show that conservation of mass can occur several of ways during a chemical reaction.

Science and Engineering Practices (SEP)

This lesson does not directly tie into any of the SEP.

Crosscutting Concepts (XC)

During this lesson students will recognize that patterns occur in science.  Students are expected to see that patterns exist in each of the 5 types of reactions they and be able to recognize each reaction based on these patterns.

Warm-up

5 minutes

The previous day students finished the lesson by categorizing 10 different reaction into the five different reactions types: synthesis, decomposition, single replacement, double replacement and combustion.  To start the class, I have each student write down on a single sheet of paper one example of each.  They are told to use their notes to aid them in this.  This activity will help them recall what was learned from the previous day.  After a five minutes I have them turn it, so that I can look at it after class. When they are done they take out their notebooks.

Explain

40 minutes

The two previous days consisted (day 1 and day 2 links) of students participating in the "Explore" stage of inquiry.  During this process they were building a personal understanding of reaction types that might not necessarily be 100% accurate, but can be used as a scaffold to create a deeper understanding through formal explanation (lecture).  This "Explain" portion of inquiry is critical because it helps students correct any misconceptions they may have attained during the Concept Attainment portion of the lesson.

Formal Notes Explanation

I find the best way to help student take notes is to make them as interactive as possible.  The Powerpoint I use was made by a coworker of mine and uses a relationship theme as analogy to represent each type of chemical reaction.  I start by showing each type of reaction using a letter representation, such as A + B -->AB, to show the process of reactants changing into products.  This is followed by the name of the reaction, an example of the reaction, finally followed with a relationship analogy.  For example, man + woman --> married couple.  The analogy provides another way for students to scaffold the information into a deeper understanding.  After explaining all the information on the slide, I perform a demo that illustrates the reaction type.  For example Mg + O2  --> MgO.  Each slide and demo takes about 7 minutes.

 Slide Explanation and Demo

All Demos should be done wearing goggles and an apron.

 Slide 1-Combination reaction demo

  • Provide generic representation of reaction, A + B --> AB
  • Provide example of reaction
  • Have them try and predict the products
  • Provide marriage analogy
  • Do demo:

Materials

For the synthesis reaction I fill 3 balloons with a small amount of different gas.  The first one contains helium, the second contains a small amount (cantaloupe size balloon) of hydrogen gas and the third is filled with a mixture of 75% hydrogen and 25% oxygen (a little smaller than the previous balloon). see video

Procedures

Behind a blast shield I first attach a helium balloon to a ring stand and ignite it using a wooden splint attached to a meter stick.  This makes a little pop.  Most kids are unimpressed.  Next I do the same with the hydrogen filled balloon.  Before igniting it, I tell them that when I throw parties I use special balloons and then ignite it.  This balloon makes a fairly loud boom and will startle some students.  I follow this up with the smallest of the balloons the hydrogen/oxygen filled balloon.  I than tell them we are going to try this again, but this time cover your ears.  This balloon make a significantly louder boom, so it’s important to warn the students.

After completing all three balloons I tell them what was in each one.  I follow this by writing the synthesis equation, H2 + O2  à H2O on the board and explain that when hydrogen and oxygen are combined they make water and release a lot of energy.  I ask them to image what the Hindenburg looked like as it was going down.

If these gasses are not present an alternative synthesis reaction that I use sometimes is the burning of Mg.  This is simple and an effective way to illustrate this type of reaction.

 Slide 2-decomposition reaction demo

  • Provide generic representation of reaction, AB à A + B
  • Provide example of reaction
  • have students predict the products
  • Provide marriage analogy
  • Do demo (see video)
  • For this reaction I do the decomposition of 30% hydrogen peroxide.

Material

  • 50-100 ml of 30% hydrogen peroxide (H2O2) solution
  • saturated potassium iodide (KI) solution
  • liquid dishwashing detergent
  • 500 ml graduated cylinder
  • Wood splint
  • Tray or tub

Directions

  • Put on gloves and safety glasses.
  • Place cylinder in tub
  • Pour ~50 mL of 30% hydrogen peroxide solution into the graduated cylinder.
  • Squirt in a little dishwashing detergent in cylinder.
  • Add ~10 mL of potassium iodide solution. 
  • Do not lean over the cylinder when you do this, as the reaction is very exothermic and you may get splashed or possibly burned by steam.
  • Place burning splint to show the presence of oxygen
  • Write H2O2 --> H2 + O2 on the board as an example.

 Slide 3-single replacement

  • Provide generic representation of reaction, AB + C --> AC + B
  • Provide example of reaction
  • have students predict the products
  • Do demo (see video)
  • For this reaction I do a single replacement reaction of copper metal in silver nitrate.

Material

  • 100 ml beaker
  • 50 ml of 0.1M silver nitrate
  • Copper wire
  • Glass stirring rod

Directions

  • Add 50 ml of silver nitrate to beaker
  • Coil one end of copper wire around a pencil. Remove from pencil
  • Take uncoiled end and wrap it around glass stirring rod.  Make the wire short enough so that the wire is just off the bottom of the beaker when the stirring rod is balanced across the top
  • Show students what the set up looks like. At the end of the class show them again.
  • Enough silver should have replaced the copper that students should see the reaction.
  • Repeat for each class and save for the next day.
  • Write reaction on the board as a second example. Cu + 2AgNO3 --> 2Ag + Cu(NO3)2

Slide 4-Double Replacement

  • Provide generic representation of reaction, AB + CD --> AC + BD
  • Provide example of reaction
  • predict products
  • Do demo (see video):

Materials

  • Test tube and test tube rack
  • 2 ml of 1 M KI solution
  • 1 ml of 0.1 M Pb(NO3)2

Procedures

  • Put KI in test tube and add a few drops of Pb(NO3)2.
  • Yellow precipitate will form
  • Show students
  • Write chemical reaction, 2KI+Pb(NO3)2-->PbI2 + 2KNO3 on the board as an additional example

Do not dump the solid down the drain.  Use filter paper to separate the solid from the liquid. Let dry and dispose of in the garbage when dry.  You can use smaller amount of each to produce less waste.

Slide 5 and 6-Combustion reaction

  • Go over contents of both slides
  • Explain that a hydrocarbon is anything with carbon and hydrogen.  It is the fuel used in chemical reactions.
  • Provide methane example
  • have students predict products
  • Do Whoosh Bottle Demo (see video):

Materials

  • 5 gallon water bottle
  • 10 ml of ethyl alcohol (do not substitute with methanol)
  • Lighter
  • Blast shield

Procedures

  • Add ethyl alcohol to water bottle
  • Swirl alcohol by rotating bottle in your hand.  Do this till the alcohol has vaporized (several turns)
  • Place bottle behind blast shield, stand off to the side and light with a match.
  • Bottle will shoot out a bright blue flame so be sure to stand back.
  • After the bottle has cooled down (1 min) show students that the remaining liquid contains water and carbon dioxide went in the air

Generally the kids love this demo because it sounds like a jet engine.  If you have difficulty igniting it the first time, add a little more alcohol, swirl and try again.

The part that is most difficult for students is predicting products. This is not the main focus of the unit but it does need to be covered. Typically they forget that some elements form diatomic molecules and also don't correctly write the chemical formulas. The only product they have to predict for the unit test is CO2 in a combustion which is memorization.  The next day's lab activity will give them more practice in predicting products.

Elaborate/Homework

5 minutes

After everyone has written the notes and seen the last demo I hand the Types of Chemical Reaction Worksheet.doc homework out (answer key).  The purpose of the homework assignment is to provide students with a final chance to categorize a variety of chemical reactions, then balance them and predict some products.  This provides reinforcement for the lab the following period.

Most students had no difficulty completing the types of reaction and balancing portion of the worksheet.  Some students had some difficulty predicting the products because they have only had limited exposure to the concept.  The predicting portion of the lesson was not the main focus of the assignment; however, they will have to recognize the products present in a combustion reaction and single replacement reactions.  Two thirds of the students that completed the assignment were able to see patterns in the reactions and were able to predict the products in problems #9, 10, 14 & 17.