4 Reaction stoichiometry: How can we make chalk?

Students will develop a process for producing calcium carbonate (chalk) that is both cost-effective and efficient. They will evaluate a variety of possible reactants for both the raw material costs and the percent yield of the overall reaction. They will create a small-scale process in the chemistry lab and then evaluate what it would take to scale up the process.

Learning outcomes

Students will:

• determine percent yield for their selected reaction
• predict the products and write balanced equations for their reactions
• create a procedure that produces calcium carbonate with a minimum loss of product
• understand the cost of reactants
• recognize the difficulty of achieving 100% yield in a chemical reaction
• appreciate the challenges involved in producing chemicals on a manufacturing scale

Teacher planning

Time required

2.5 class periods (85 minutes each)

Materials needed

• lab equipment typical for a high school chemistry classroom, including:
  • filter paper
  • funnel
  • graduated cylinders
  • distilled water
  • bottles
  • test tubes
  • beakers or Erlenmeyer flasks
• possible reactants:
  • calcium acetate monohydrate
  • calcium chloride anhydrous
  • calcium nitrate tetrahydrate
  • ammonium carbonate anhydrous
  • sodium carbonate anhydrous
  • potassium carbonate anhydrous
• table one listing approximate costs of reactants (Table one also appears on the student sheet.)
• “How can we make chalk?” student activity sheet — one copy for each student
• class data table copied as an overhead transparency or reproduced on the board
• optional: copies of class data table for students
• optional: overhead projector — required if you will project the class data table

Pre-activities

• Students should have an understanding of types of reactions, mole conversions, molarity and stoichiometry.
• Students should understand how to filter a precipitate using a funnel and filter paper.
• Prior to the lesson, prepare for the lab by doing the following:
  1. Create lab groups with no more than four students per group. This lab assumes eight lab groups with four students per group.
  2. Prepare the 0.5 M solutions of each reactant. Table two provides data to prepare 200 ml of each solution. (Table two also appears on the student sheet.)
  3. Prepare three 50-ml bottles of each solutions and label these bottles.

Activities

Day one: Introduction

1. Hand out the “How Can We Make Chalk?” student activity sheet and have the students read it. The activity sheet presents the following scenario:
   

   As a new hire for a major chemical manufacturer, you are in charge of an efficiency analysis for the production of calcium carbonate (also known as chalk). Your group is to determine the best method for making chalk with the lowest cost. In order to do this, you will need to determine the possible reactions that will produce calcium carbonate from the list of possible reactants. You will need to determine the cost of these possible reactants and you will need to perform the reactions at least twice in order to determine the percent yield for each reaction. Prior to performing any experiments, your group will submit a short report to your boss.



A simple filtering set-up is shown here.

2. Demonstrate the filtering process for students. Show them how to fold the filter paper and prepare to set up the funnel as shown in the picture. Remind students that they will not be able to get the calcium carbonate off the filter paper. Prompt them to explain that they will need to know the mass of the filter paper prior to filtering so that they can subtract its mass from the mass of the chalk and filter paper in order to determine the mass of the chalk produced.
3. Have students work on the pre-lab proposal report during class. They will submit one copy of this report to the teacher prior to the end of class and retain a copy for their use on lab day. As described on the student data sheet, the pre-lab proposal should contain the following:
   • List of all possible reactions that can be performed in order to produce calcium carbonate from the available reactants listed in the materials list. These reactions must be written as balanced equations.
   • List of cost-per-gram of reactant for each of the possible reactants as well as the supplier. Students should assume they will purchase the solid and lab grade for each of the reactants.
   • The procedure the students will follow in order to perform these reactions. Students will be given only 50.0 ml of 0.5 M solutions of their 2 reactants to use. They will need to specify in their procedure the volume of each of these solutions that they will use. The student sheet reminds students to onsider that they may need to perform several trials from that 50 ml sample.
   • Report conclusion stating the reaction they would most like to perform and an explanation of their choice.
4. As students submit their pre-lab reports, review and approve each group’s selected reaction and record this in the class data table labeled “How can we make chalk? lab.”
5. After reviewing and approving proposals, you may ask some groups to perform a reaction other than the one they selected so that each group is performing a different reaction. This allows for data to be collected on eight different reactions so that the most efficient can be selected from the class data.

Day two: Lab

1. Remind students that they should plan to run at least three trials and they need to determine what volume of the reactant solutions they should use in order to ensure they require no more than the 50 ml they will be given.
2. Have students create a data table to hold all the data collected during the lab as well as any calculated results.
3. Require students to have their data tables checked and initialed by the teacher. Provide each group with 50 ml of each reactant as well as three sheets of filter paper. Have students perform their reactions. Be prepared to provide additional filter paper to students in case it is accidentally torn.
4. Allow the filter paper to dry overnight in the classroom prior to determining the final mass.

Day three

1. Have students record their final masses and perform their calculations of yield, percent yield, average percent yield, and cost per gram of calcium carbonate produced.
2. Have students enter their average percent yield data and cost per gram of chalk data onto the class data table.
3. Have students copy the class data. You may provide paper copies of the data table to aid in this process.
4. Conclude this activity with a class discussion to include the following points:
   • Are there any results that do not seem to fit with the rest of the data?
   • If so, what happened with that particular reaction? As a class, determine if this data can be considered valid data.
   • What new techniques, ideas, or concepts did you use or learn?
   • Should we consider the fact that we can sell the chalk in our cost analysis for this reaction?
   • Can you think of ways to improve this activity?

Assessment

Assess students on their pre-lab proposal reports using the proposal rubric. Assess students’ final lab reports using the “Let’s Make Chalk” lab rubric. Requirements and rubrics for both reports appear on the student sheet.

Modifications

This activity is written for honors chemistry students. In order to use it with academic chemistry students, some additional preparation before the lesson would be necessary:

• Review the idea that a double replacement reaction that produces a precipitate will occur between your reactants.
• Discuss how the reactants provided can be used to produce the desired solid calcium carbonate.
• Have students write the nine possible reactions with their lab groups.
• Once the reactions are written, bring the class together to brainstorm possible procedures for this lab. Keep a rough outline of this procedure on the board.

At this point students can proceed with the “day one” activities.

Academic students may also need to have the data table provided for them prior to the “day two” activities.

Critical vocabulary

• filtration
• filtrate
• precipitate
• theoretical yield
• actual yield
• percent yield

• Next: What is heat? — Heat vs. temperature

National Standards

In addition to meeting objectives of the North Carolina Standard Course of Study, this lesson plan addresses the following national standards.

National Science Content Standard A

All students should develop an understanding of:

• Abilities necessary to do scientific inquiry
• Understandings about scientific inquiry

National Science Content Standard B

All students should develop an understanding of:

• Structure of atoms
• Structure and properties of matter
• Chemical reactions

• Next: What is heat? — Heat vs. temperature
• Previous: What element would you be?

Author’s note

This activity is written for honors chemistry students. See “modifications” for ideas on adapting it for academic chemistry students.

Learn more

Related topics

• Search LEARN NC for more resources on chalk, chemistry, hands-on, higher-order thinking, inquiry, labs, science, and stoichiometry.