Lesson 2. Lesson 2: What Happens to Mass During a Chemical Reaction?

Carole Namowicz
Chemistry
100 min
High School Honors Chemistry
v2

Overview

Students will perform two different experiments where they are asked to record the overall mass of the reactants and products before and after the reactions takes place. Both experiments will be "closed system" experiments where any gases produced will be trapped by either parafilm or a balloon. Students should observe that overall mass should remain the same before and after each experiment leading them to the law of conservation of mass. This proves that a carbonated beverage can be produced via a chemical reaction.

Standards

Next Generation Science Standards
  • Physical Science
  • NGSS Practice
    • Using Mathematics
  • NGSS Crosscutting Concept
    • Energy
Computational Thinking in STEM
  • Data Practices
    • Analyzing Data
  • Modeling and Simulation Practices
    • Assessing Computational Models
    • Using Computational Models to Understand a Concept
  • Systems Thinking Practices
    • Defining Systems and Managing Complexity
    • Thinking in Levels
    • Understanding the Relationships within a System

Credits

Unit designed by Carole Namowicz a teacher at Lindblom.

Activities

  • 1. Experiment 1
  • 2. Experiment 2
  • 3. Reflecting on the Experiments
  • 4. Reviewing the Data
  • 5. Analyzing Results
  • 6. The Law of Conservation of Matter (Mass)
  • 7. Evaluating the Law of Conservation of Matter
  • 8. Where did the bubbles come from?

Student Directions and Resources


You will perform two different experiments in order to determine what happens to matter (mass, because all matter has mass) during a chemical reaction.

1. Experiment 1


Mg (s) + HCl (aq)  ----->  MgCl2 (aq)   +   H2 (g) 
bracket   bracket
Reactants   Products

 

  1. Place a weighing boat on your balance and zero it out.
  2. Measure out 0.2 g of magnesium in the weighing boat.
  3. Record the mass of a 125 mL Erlenmeyer flask.
  4. Measure out 15 mL of 0.5 M HCl in a 25 mL graduated cylinder.
  5. Pour the 15 mL of 0.5 M HCl into the flask and record its mass.
  6. Subtract the mass of the flask itself to determine the mass of the HCl only.
  7. Add the mass of the Mg and the HCl, record this total mass below. (This is the total mass of your reactants.)
  8. Separate a small square of parafilm from its backing paper and record its mass.
  9. Pour the Mg from the weighing boat into the flask full of HCl (still on the balance), then immediately cover the flask with parafilm so no gas is allowed to escape.
  10. Place the flask (still covered with parafilm) back onto the balance.
  11. Subtract the mass of the flask + the parafilm from the mass on your balance, then record that mass. (This is the total mass of your products.)
  12. Record any observations of what occurred during the chemical reaction below. Observations include describing what happened during the reaction and noting differences between the reactants and products.
  13. Dump the contents of the flask down the appropriate drain, rinse it out, and place it on the drying rack.

Question 1.1

Record your data from Experiment 1: Mg (s) + HCl (aq) → MgCl2 (aq) + H2 (g)



Question 1.2

Record your observations from Experiment 1: Mg (s) + HCl (aq) → MgCl2 (aq) + H2 (g)

2. Experiment 2


NaHCO3 (s)  +  CH3COOH (aq)  ----->  NaC2H3O2  (aq)  +   H2O (l)  +  CO2 (g)
bracket    bracket
Reactants   Products
  1. Record the mass of a 125 mL Erlenmeyer flask and record the mass of your balloon.
  2. Measure 20 mL of 1.0 M acetic acid (CH3COOH) in a 25 mL graduated cylinder. Pour this into the empty 125 mL Erlenmeyer flask.
  3. Place a weighing boat on your balance and zero it out.
  4. Measure out 0.6 g of baking soda (NaHCO3) in the weighing boat, then pour it carefully into your balloon.
  5. Place the baking soda balloon and the acetic acid flask on the balance. Subtract the mass of the flask and the balloon from the mass on your balance and record that mass. (This is the total mass of your reactants.)
  6. Carefully attach the balloon to the flask making sure not to empty any of the baking soda into the flask in the process!
  7. Once the balloon is secure on the flask, shake the baking soda into the flask so it reacts with the acetic acid. Wait until all of the material seems done reacting.
  8. Record any observations of what occurred during the chemical reaction below. Observations include describing what happened during the reaction and noting differences between the reactants and products.
  9. Record the total mass after the reaction by again subtracting the mass of the flask and the balloon from the mass on your balance. (This is the total mass of your products.)
  10. Dump the contents of the flask down the appropriate drain, rinse it out, and place it on the drying rack. Return the balloon to your instructor.

Question 2.1

Record your data from Experiment 2: NaHCO3 (s) + CH3COOH (aq) → NaC2H3O2 (aq) + H2O (l) + CO2 (g)



Question 2.2

Record your observations from Experiment 2: NaHCO3 (s) + CH3COOH (aq) → NaC2H3O2 (aq) + H2O (l) + CO2 (g)

3. Reflecting on the Experiments


The overall reaction for experiment 1 was expressed as: Mg (s) + HCl (aq) → MgCl2 (aq) + H2 (g)

The overall reaction for experiment 2 was expressed as: NaHCO3 (s) + CH3COOH (aq) → NaC2H3O2 (aq) + H2O (l) + CO2 (g)

Look carefully at how both of these chemical reactions are written and then think back to the actual experiments you completed in order to answer the questions below.

 


Question 3.1

Each chemical formula was followed by an abbreviation of one or two letters in parentheses. Identify each of the following abbreviations to the best of your ability



Question 3.2

Explain why adding these abbreviations to a chemical reaction can help your understanding of what is occurring when you perform the experiment.

4. Reviewing the Data


Grab a large whiteboard and make a table of your results from both experiments. Set up your table as shown below.

  Mass of Reactants Mass of Products
Experiment 1    
Experiment 2    

 


Question 4.1

Compare the mass of the reactants and products for experiment 1. What observation(s) do you make when comparing these two masses?



Question 4.2

Now compare the mass of the reactants and products for experiment 2. What observation(s) do you make when comparing these two masses?

5. Analyzing Results


What happens to mass during a chemical reaction? Review your class data from the two experiments and explain what happens to the overall mass of the reactants and products.


Question 5.1

1. What claim can you make about the change in mass from your total reactants to your total products?



Question 5.2

2. What evidence from your experiments do you have that matter (mass) is conserved in a chemical reaction? Be sure to explain what it means to be "conserved" in your answer.

6. The Law of Conservation of Matter (Mass)


The law of conservation of mass states that matter (mass) cannot be created or destroyed. Therefore the total mass of the reactants in a chemical reaction must be equal to the total mass of the products. How then is it possible to"lose" weight?


Question 6.1

1. If someone loses weight, is that a violation of the law of conservation of mass? Explain why or why not.



Question 6.2

2. Where do you think the matter (mass) goes when a person loses weight?

7. Evaluating the Law of Conservation of Matter


Watch the video below and answer the question that follows.

 


Question 7.1

1. Now that you have watched the video, do you agree with your original explanation of where the matter (mass) goes when a person loses weight? Explain why or why not.



Question 7.2

2. According to the video, does carbon dioxide gas have mass? 

8. Where did the bubbles come from?


In the last lesson, you watched while your instructor carbonated a beverage in front of you without a SodaStream.


Question 8.1

1. If the total mass of the reactants (citric acid + sodium bicarbonate) in the weighing boats before the reaction took place was approximately 2.5 grams, estimate the mass of the total products in the beaker of water after the reaction took place.



Question 8.2

2. Did your instructor cover the top of the products (the carbonated beverage) with a balloon or parafilm after mixing the reactants together? Think about how this may affect your answer to the previous question.