Summary

In this lesson students will complete a series of double replacement reactions to form precipitates. The precipitates will be used as a pigment to create paint.

Grade Level

High School

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-1: Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
• HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
• HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
• HS-PS1-4: Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.
• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data
  • Engaging in Argument from Evidence

Objectives

By the end of this lesson, students should be able to

• Write and perform double replacement reactions to form precipitates.
• Use solubility rules to identify precipitates.
• Identify the electron configuration for transition metals.
• Create paint using pigments and two different binders.

Chemistry Topics

This lesson supports students’ understanding of:

• Atomic Structure
• Electrons
• Orbitals
• Electron Configurations
• Ionic Bonding
• Transition Metals
• Chemical Reactions
• Double Replacement Reactions
• Precipitates

Time

Teacher Preparation:

Lesson:

• Engage: 10 minutes (note: chemicals for demonstration must be prepared 1 – 2 days in advance)
• Explore: 45 minutes
• Explain: 20 minutes
• Elaborate: 5 minutes
• Evaluate: 5 minutes

Materials

Demonstration:

• 2.0 g Fine (grade 0000) steel wool
• 600 mL White vinegar
• jar with loose fitting lid or holes in lid to make iron acetate
• 15 mL clear ammonia
• 15 mL 2% hydrogen peroxide
• Graduated Cylinder
• Clear Container (ex: test tube or flask)
  

Lab (per student group):

• 2 – 250 mL Erlenmeyer flasks
• Funnel, 9.5 cm across
• Ring Stand with ring
• 12.5 cm filter paper
• 50 mL Solutions (1M):
  • Copper (II) sulfate, CuSO₄
  • Sodium Carbonate, Na₂(CO₃)
  • Iron (III) chloride, FeCl₃
• 50 mL Solutions (0.1 M):
  • Copper (II) chloride, CuCl ₂
  • Ammonium hydroxide, NH₄OH
  • Potassium ferrocyanide, K₄[Fe(CN)₆]
  • Sodium hydroxide, NaOH
• Wash bottle with distilled water
• Paint brush
• 1 raw egg
• Wax coated paper plate
• Straight pin
• Scrap paper
• Linseed oil

Safety

• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required
• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• If Linseed oil is spilled, exercise caution when disposing of paper towels used for this spill; as Linseed oil dries, it is very exothermic.

Teacher Notes

• Engage: Show students the stop-and-go demonstration. Note that materials will need to be prepared 1-2 days in advance.
• This is a common oxidation-reduction demonstration, and it will allow students to view a transition metal forming different compounds and changing colors. While showing the demonstration, have students look at the color wheel on the student page. This would be a good opportunity to discuss with students how the chemicals in the demonstration are interacting with light. For example, the solution appears red because it is transmit red light and absorbing green light, and then it switches as the hydrogen peroxide is added.
• Materials for this demonstration can all be purchased at a discount store, such as Walmart.
  • Stop-and-Go Demonstration Procedures:

1. Make iron (II) acetate 1 -2 days prior to using the demonstration. Steps 2 and 3 describe how to make iron (II) acetate from white vinegar and steel wool. This solution will need at least 48 hours to form and is needed for the demonstration.
2. Use scissors to cut the 0000 grade steel wool from the bundle and then measure the mass to get 2.0 grams. You may have to cut additional pieces from the bundle or remove pieces to obtain 2.0 grams of the steel wool. Wear gloves when handling steel wool.
3. Mix 600 mL of white vinegar with 2.0 g extra fine (0000 grade) steel wool in a jar with lid loosely placed on the jar. During the 48 hours, while the iron acetate is forming, open the jar to allow the gases escape.
4. Measure 30.0 mL of finished iron (II) acetate and place in clear container for easy viewing by students.
5. Add 15.0 mL clear household ammonia to the clear container and solution will turn red. This could be done in a large test tube or flask.
6. Add 15 mL 2% hydrogen peroxide to solution and it will turn green.

• Inform students that this demonstration works because iron is a transition metal with an unfilled d-orbital. Iron is stable with two different electron configurations and can therefore form compounds with different ions. Have students locate iron on the Periodic Table and identify its electron configuration so they can see that it’s d-orbital is not full; this will also be covered in the pre-lab questions. Explain to students that transition metals with unfilled d-orbital can form various ions with different charges and therefore different compounds. Transition metals will form a compound to become most stable.

• Explore: In this lab, students will perform double replacement reactions to form stable solid precipitate. Each reaction will include a compound containing a transition metal. Students will use the precipitate to make paint. Students should be familiar with using solubility rules to predict solid precipitates.

• Answer Key for Pre-lab Questions:

1. What is the electron configuration of iron?
   1s ²2s²2p⁶3s²3p⁶4s²3d⁶ or [Ar] 4s²3d⁶
2. Complete the electron configuration diagram for iron using arrows to show the locations of electrons.
   
3. How many unfilled 3d subshells does iron have?
   4
4. When the solution in the demonstration appeared red, what color of light was it reflecting? What complementary color did the solution absorb?
   When the solution appeared red, it was transmitting red light, and was absorbing green.
5. Which other elements would you expect to form compounds with multiple colors? Explain.
   Students should be able to identify other transition metals such as cobalt, or copper due to their location on the Periodic Table and the fact that their d-orbitals are only partially filled.

• Following these pre-lab questions, describe how iron is stable giving away 2 electrons to become Fe²⁺ (the ferrous ion) or three electrons to become Fe³⁺ (the ferric ion).
• Teacher Note: Some of the transition metal complexes formed here are transition metal ions, while others are transition metal compounds. This idea is eliminated from the background information.

• Part 1 Data:

1. CuSO₄ (aq) + Na₂CO₃ (aq) → CuCO₃ (s) + Na₂SO₄ (aq)
2. CuCl₂ (aq) + 2 NH₄OH (aq) → Cu(OH)₂ (s) + 2NH₄Cl (aq)
3. 4FeCl₃ (aq) + 3K₄[Fe(CN)₆] (aq) → Fe₄[Fe(CN)₆]₃ (s) + 12KCl (aq)
4. FeCl₃ (aq) + NaOH (aq) → Fe(OH)₃ (s) + NaCl (aq)

• Explain: Students will use the reactants to complete the chemical equations for each double replacement reaction. You will need to provide students with solubility rules so they can determine the identity of the solid precipitate formed in each reaction. Students will observe the color of each precipitate, then use the color wheel to complete the data table.
  
  After creating paint with water and oil based binders, students will use their prepared paints and attempt to cover the 1 cm square on the data table with one brush stroke. Students should look carefully at the painted square and evaluate the color, coverage and line produced by each paint. After the paint dries, students will notice that the darker color paint is more easily rubbed off and that the linseed based paint adheres to the paper less than the egg/water based paint.

• Elaborate:Students will compare the two types of binders, water and oil based, utilized in this experiment. Encourage students to utilize their data to compare the two types of paint. Students could do additional research on types of paint if needed.

• Evaluate: As students complete their response about paint to be used for a backdrop, they should be able to explain the process used to make the paint from the precipitate formed by the double replacement reaction. Students will need to use evidence from their painted squares to determine their selection for a binder to make the paint.

• Use the rubric below as a guide to assist in evaluating student responses.