Balancing Chemical Equations Using a Tactual Model

By Laura Hospitál on Nov 06, 2015

Many thanks to Sasha Hospitál for developing the idea for this activity.

This activity came out of a conversation with my daughter, Sasha.  I explained that I had begun teaching my 8th grade class how to balance chemical equations and I sensed that my students were a bit frustrated.  I told Sasha that they needed a more tactual model of the atoms (making up the molecules) involved in a chemical equation in order to understand this concept better.

The equation for which she developed this activity is used as the basis for the description, but any simple equation could be used. The size of the pom-poms should be (approximately) modified accordingly.  The equation is:  H2 + O2 yields H20

My daughter thought about this and envisioned using pom-pom craft balls of various sizes to represent the atoms of hydrogen and oxygen in the equation.  After a quick trip to Wal-Mart for supplies, the following activity is what resulted from her efforts. 

This activity should be introduced after the students have learned the Law of Conservation of Mass and the most basic information about chemical reactions and balancing equations.

Preparation:

  1. Cut out small pieces of Velcro Tape (hook) for each pom-pom craft ball to represent each atom in the equation.  Use smaller pom-pom craft balls for smaller atoms and larger pom-pom craft balls for larger atoms.  Prepare one extra pom-pom craft ball for each element for the key. It is possible to buy rounds of velcro but I think that they would be too big for some of the pom-pom craft balls.   
  2. Afix the tape to each pom-pom craft ball.
  3. Count out enough atoms of each element for each student and store in ziplock bags.  For the equation mentioned, this would be 8 small craft pom-pom balls (Hydrogen) and 4 large craft pom-pom balls (Oxygen)
  4. Prepare braille and LP keys as follows: (I only thought of this after the activity but it would help the students.)

Braille

       a. Braille   "Key for Tactile chemical equation - H+ O2 yields H20 (or your equations) " on the top of the page.
       b. Space down 4 or 5 times
       c. Braille the chemical symbol and name of one element, e.g. Hydrogen (H) 
       d. Space down 3 spaces and braille the next element, e.g. Oxygen (O)
       e.  Afix a pom-pom craft ball of the appropriate size next to each element.

Large Print

       a. Using card stock print the heading "Key for Tactile chemical equation - H+ O2 yields H20 (or your equation) in 24 pt. bold or appropriate format on the type of the page
       b.  Space down 6 times
       c.  As per the braille instructions, type the name and chemical symbol of the smallest element, e.g.  Hydrogen (H) 
       d. Space down 3 spaces and type the next element, e.g. Oxygen (O)
       e.  Afix a pom-pom craft ball of the appropriate size next to each element.

Materials

  • Pom-Pom Craft balls of various sizes - I would recommend purchasing them at a craft store and asking for some that will not shed, as the craft balls we used shed. You will need enough craft balls to have one for each atom of each element in the equation and one extra of each element for the key.  See Preparation section. 
  • Velcro tape (hook side) 
  • Felt board for each student - APH has a nice model that was large enough.  Please see the following review: https://www.perkinselearning.org/accessible-science/aph-felt-board  The large board that comes with the AZER Periodic Table set was large enough for 2 students to share it. 
  • Perkins Braillewriter
  • braille paper
  • printer
  • computer
  • Yields signs (arrows) from the AZER set.  If not available, this can be easily built.
  • Coefficient numbers from the AZER set as necessary.  Braille or print numbers can substitute with velcro tape afixed to the back.

Procedure

  1. Pass out the Ziplock bags with the "atoms" inside and a key for each student. 
  2. Explain to the students that today's lesson will be balancing an equation, but that they will not use pencil and paper or a braillewriter.
  3. Give students a moment to look at the key and the materials. 
  4. Assist students as they set up the equation.  For the sample equation, read the equation several times to students. Assist only after several minutes, if necessary.  Most of my students were able to do this.   (See picture.)
  5. Have students count the number of hydrogen atoms (H) on the left side of the equation (reactants) and the right side (products). Remind the students of these terms as they work.  They will find that they are the same. 
  6. Have students count the oxygen (O) atoms on either side.  They will find that there are more oxygen atoms on the reactant side. Ask them what they should do.  If some students try to add O to H2O, remind them that we can't change the composition of any of the reactants or products, but only increase the number of molecules as necessary.  I told the students the difference between H2O and H2O2.  Next year, I will bring some hydrogen peroxide to demonstrate the difference one atom can make. Students should eventally think about adding another H2O molecule. Let them figure this out themselves, though.  
  7. After adding a second H2O molecule, (see photo), ask students to recount the Hydrogen (H) atoms.  They will find that now there are 2 on the reactant side and 4 on the product side.  Ask: What should we do?  Students should determine that adding another H2 will solve the problem.  
  8. Have students count both Hydrogen (H) atoms on the reactant and product side of the arrow and the Oxygen atoms.
  9. Once they have determined that the equation is balanced, students will be asked to remove the 2nd molecule of each (those added) and to replace them with the number 2.  Students will read the equation aloud.

 

Variations

As per the instructions above, any simple chemical equation can be modeled. 

NGSS Standards:

Middle School:  PS1.B: Chemical Reactions:
Substances react chemically in characteristic ways.  In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants.
(MS-PS1-2), (MS-PS1-5) 
The total number of each type of atoms is conserved, and thus the mass does not change.  (MS-PS1-5)
 
 
High School:  PS1B:  Chemical Reactions:
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. (HS-PS1-2),(HS-PS1-7)
 
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