The teacher will perform a demonstration that requires the students to use their knowledge of single-replacement and double-replacement reactions to distinguish between the two types of reactions. The students will also make predictions, observations, and explanations about the products that will form when a chemical reaction takes place.
Learning Objectives: What will students know and be able to do as a result of this lesson?
Use only reactants to distinguish between single-replacement and double-replacement reactions.
Prior Knowledge: What prior knowledge should students have for this lesson?
Classify both single-replacement and double-replacement reactions.
Predict the products of both single-replacement and double-replacement reactions.
Apply solubility rules to predict the states of matter of the products for double-replacement reactions.
Metallic single-replacement reactions depends on the reactivities of the single metal.
Use the activity series to predict whether or not a metallic single-replacement reaction will take place (H may act as a metal).
Guiding Questions: What are the guiding questions for this lesson?
Are you viewing a single-replacement reaction or a double-replacement reaction? Explain your reasoning.
Predict: What event, related to the focus topic, that may surprise students, will the students make a prediction about?
The students will be predicting if the following sets of reactants will produce a single-replacement or double-replacement reaction:
Set 1: BaCl2 (aq) + Na2CrO4 (aq) -->
Set 2: Fe (s) + CuCl2 (aq) -->
The teacher should have two separate demonstration tables set up: one for Set 1 and the other for Set 2.
You will need two small test tubes. Label one test tubes as BaCl2 and the other as Na2CrO4.
Place 4 drops of BaCl2 in the small test tube labeled BaCl2.
Place 4 drops of Na2CrO4 in the test tube labeled Na2CrO4.
Allow the students to observe each test tube.
The students should look for solids and the color of each solution.
The students should record their observations in the data table located on the attached Student Handout.
Pour the 4 drops of BaCl2 into the test tube containing the Na2CrO4.
Allow the test tube to sit for approximately 3 minutes.
Allow the students to observe the reaction that took place. The students should record their observations in the data table located on the Student Handout.
You will need one small test tube. Label the test tube as CuCl2.
Use a 10 mL graduated cylinder to measure 10 mL of CuCl2.
Pour the 10 mL of CuCl2 into the test tube labeled CuCl2.
Allow the students to observe the test tube containing the CuCl2 and the iron nail (before it is dropped into the CuCl2 solution).
The students should record their observations in the data table located on the Student Handout.
Drop the nail into the test tube containing the CuCl2.
After 10 minutes allow the students to observe the combination of the CuCl2 and iron nail.
The students should record their observations in the data located on the Student Handout.
The students will record their predictions and justifications in the data table located on the Student Handout.
Observe: What will the students observe and/or infer during this step of the lesson? How will students communicate their observations and inferences?
What will students be asked to observe and/or make inferences about the phenomenon/event?
The students will be making observations that will aid them in determining if their predictions about classifying the two sets of reactants as single or double replacement reactions are acceptable.
For Set 1, the students will notice:
Before mixing: BaCl2 is clear and Na2CrO4 is yellow
After mixing: A solid yellow precipitate (BaCrO4) is formed and an aqueous solution of NaCl is produced.
These observations will reveal to the students that they should have predicted set 1 as a double-replacement reaction.
For Set 2, the students will notice:
Before combining: CuCl2 is a blue solution and the iron nail has a silver color.
After combining: Copper, a bronze color, starts to form on the nail and iron began to go into the solution creating FeCl2. The solution becomes lighter in color (a lighter blue color).
These observations will reveal to the students that they should have predicted set 2 as a single-replacement reaction
How will students record their observations and inferences?
The students will record their observations in the data table located on the POEstudent.doc.
See the instructions for setting up the demonstration/lab under Predict for when the students should make observations.
How will you check for student understanding?
While the students are making their predictions and observations, the teacher takes on the role as facilitator and roams throughout the class listening to student conversations. During this facilitation phase the teacher will probe students that may have misconceptions.
Probing is when the teacher asks the student questions to guide them to the correct answer without giving them the actual answer.
Explain: How will students be encouraged to develop explanations using their observations and scientific or mathematical concepts or principles?
How will students share their observations and inferences?
The students will share their observations with their shoulder partners (partner they are sitting next to) and their face partner (partner they are sitting in front of).
While the students are sharing with their face and shoulder partner, the teacher is a facilitator, roaming throughout the class probing students as needed to ensure each student understands the demonstrations.
Instructions for leading the closing discussion:
The teacher should divide the board in the classroom into half. Write set 1 reactants on one side and set 2 reactants on the other side. If the teacher does not have a board they may use a large sheet of paper instead.
Set 1: The teacher should point out that the two reactants are ionic (cation and anion present) aqueous solutions; therefore, this reaction would be a double-replacement reaction.
Set 2: The teacher should point out that one of the reactants is a single-element and the other is an ionic aqueous solution; therefore, it is a single-replacement reaction.
Key talking points about the phenomenon:
Set 1: Concerning the demonstration, a solid (precipitate) and an aqueous solution were formed, which are indicators of a double-replacement reaction.
Set 2: Concerning the demonstration, Copper, a bronze color, starts to form on the nail and iron began to go into the solution creating FeCl2. The solution becomes lighter in color (a lighter blue color). The single element is displacing the metal in the solution, which is what occurs during a single replacement reaction.
Common errors/misconceptions to anticipate and how to respond:
Students often struggle with distinguishing between single- and double-replacement reactions when both the reactants and products are not provided. Therefore, the teacher should point out that when the two reactants are ionic (cation and anion present) aqueous solutions the reaction will be a double-replacement reaction, and when one of the reactants is a single-element and the other is an ionic aqueous solution the reaction will be a single-replacement reaction.
How will the students show that they met the learning objectives?
The students will show they have met the learning objectives by completing the summative assessment located on the Student Handout.
The teacher will grade the summative assessment and use the student data to determine how well the students understood the learning objectives.
Specific suggestions for conducting Formative Assessment can be found in the Observe phase of the lesson where it says, "How will you check for student understanding?"
Once the teacher completes the closing discussion, key talking points, and common errors/misconceptions he or she will have the students to complete the student evaluation located at the end of the attached Student Handout.
While the students are completing the evaluation, the teacher will roam throughout the class taking note of each student’s response. By reading the students responses the teacher will be able to determine how well the students comprehend the learning objectives for the day.
After visiting each student the teacher will reiterate the closing discussion, key talking points, and common errors/misconceptions, if necessary. Then move on to completing the summative assessment.
Feedback to Students
Specific suggestions for providing Feedback to Students can be found in the Explain phase of the lesson where it says, "Common errors/misconceptions to anticipate and how to respond."
Accommodations & Recommendations
Provide the students with a peer tutor to constantly provide reminders that when the two reactants are ionic (cation and anion present) aqueous solutions the reaction will be a double-replacement reaction, and when one of the reactants is a single element and the other is an ionic aqueous solution the reaction will be a single-replacement reaction.
Have the students that have shown mastery of the learning objectives to predict the products with the correct states of matter and balance the chemical equations.
Concerning the extension, you may want to review when the students should use solubility rules and the activity series. The students should use the solubility rules to determine the states of matter for double-replacement reactions and the activity series to determine if single-replacement reactions will take place.
To create the 1 M Copper (II) chloride solution, CuCl2, dissolve 170.5 g of CuCl2 in 1 liter of distilled water, then stir.
To create the 0.1 M Barium chloride solution, BaCl2, dissolve 2.4 g of BaCl2 in 100 mL of distilled water, then stir.
To create the 0.2 M Sodium chromate solution, Na2CrO4, dissolve 3 g of Na2CrO4 in 100 mL of distilled water, the stir.
Set 2: The reaction between Fe (s) and CuCl2 (aq)
The iron nail and the solid copper that precipitates onto the nail may be thrown into the trash, and the reaction solution produced can go down the drain with excess water (Pearson Chemistry Laboratory Manual, 2012).
Set 1: The reaction between BaCl2 (aq) and Na2CrO4 (aq)
Because only drops of these solutions were used these materials can realistically go down the drain (Pearson Chemistry Laboratory Manual, 2012).
0.2 M Sodium chromate, Na2CrO4, is toxic and corrosive and may cause skin and eye injury. Wash hands thoroughly if any comes in contact with your skin.
Compounds containing barium are poisonous. Wash hands thoroughly if any comes in contact with your skin.
1 M copper (II) chloride, CuCl2, is toxic and an irritant. Wash hands thoroughly if any comes in contact with your skin.
Wear safety goggles and gloves while performing the demonstration.
Source and Access Information
Name of Author/Source: Lenora Henderson
District/Organization of Contributor(s): Washington