CT-STEM

Overview

In this lesson, students will observe a double displacement reaction where varying amounts of each reactant are used. They will be asked to focus on the amount of one product in the reaction and how the amount of that product changes relative to the amounts of each reactant used. The goal of the lesson is for students to understand the molar relationships in a reaction and why adding coefficients to a reaction is sometimes necessary.

Standards

Next Generation Science Standards

Physical Science

[HS-PS1] Matter and its Interactions

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. Amounts in Chemical Reactions
2. Exploring the Simulation
3. Varying the Amounts
4. Varying the Amounts Further

Student Directions and Resources

In this lesson, you will be asked to focus on the amount of one product in a reaction and how the amount of that product changes relative to the amounts of each reactant used. The goal of the lesson is to understand the best possible combination of reactants to use in a reaction so none of the reactants go to waste.

1. Amounts in Chemical Reactions

Observe as your instructor demonstrates the reaction of magnesium metal and hydrochloric acid to produce hydrogen gas (magnesium chloride is also produced in solution). Your instructor will use varying amounts of magnesium metal and hydrochloric acid in each flask. These amounts have been measured in moles and are represented in the table below.

Question 1.1

Record your observations about the relative amounts of hydrogen gas produced in each reaction in the table below.

Question 1.2

Did any of the reaction combinations appear to produce roughly the same quantity of hydrogen gas? If so detail which combinations of magnesium metal and hydrochloric gas below.

Question 1.3

Did any of the reaction combinations leave unreacted excess magnesium? If so detail which combinations of magnesium metal and hydrochloric gas below.

2. Exploring the Simulation

Experiment with the simulation by varying amounts of the two reactants. Be sure to hit "setup" after adjusting amounts or the change will not be reflected in the simulation. After you feel you have learned all the features of the simulation move on to answer the questions below:

Question 2.1

What is represented by the grey circles in the simulation? Explain how you know this.

Question 2.2

The box "hide-molecules" was checked when you opened the simulation. Describe what happens when you uncheck this box.

Question 2.3

What is represented by the green circles? Explain how you know this.

Question 2.4

Is the simulation more like the real world reaction with the "hide-molecules" box checked or unchecked? Explain why.

Question 2.5

What is the purpose of including features in a simulation that do not mimic the real world?

3. Varying the Amounts

The simulation below models the same reaction your instructor demonstrated, but now you have control over the amounts of both reactants being used.

Directions:

Adjust the slider bars to vary the amounts of each reactant (Mg and HCl) as instructed in the table below.
Then press "setup". The values you've selected for each reactant will now appear in the box at right. Moles of magnesium are represented by the grey circles and moles of hydrochloric acid (HCl) are represented by the green circles in the blue rectangle.
Now press "go" and observe how much H₂ gas is produced with each combination of reactants. All amounts are again measured in moles.

Question 3.1

Record the amount of hydrogen gas produced in each reaction in the table below.

Question 3.2

Did any of the reaction combinations produce the same quantity of hydrogen gas (within 0.2 moles)? If so detail which combinations of magnesium metal and hydrochloric gas below.

Question 3.3

Did any of the reaction combinations leave unreacted excess magnesium? Unreacted excess magnesium is grey circles leftover on the bottom of the container when all green circles of hydrochloric acid have disappeared because they reacted. If so detail which combinations of magnesium metal and hydrochloric gas below.

4. Varying the Amounts Further

Now you will use the same simulation, but this time you have control over the amounts of each reactant you will use.