In this lesson students will use solubility rules to predict whether the product of a double displacement or metathesis reaction will produce a precipitate. Students will then investigate a series of reactions to verify solubility rules. Finally students will determine the identity of unknown solutions based on experimental evidence.
- MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
- 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.
By the end of this lesson, students should be able to
- Write a net-ionic equation for a double displacement or metathesis reaction.
- Predict whether the product of a double displacement reaction will be soluble or insoluble.
- Use experimental evidence to identify an unknown solution.
This lesson supports students’ understanding of
- Solubility rules
- Net-ionic equations
- Double displacement reactions
- Precipitation reactions
Teacher Preparation: 60-90 minutes (first time), then 15-30 minutes for recurring use
- Engage: 15-45 minutes
- Explore:90-180 minutes
- Explain: 45-90 minutes
- Elaborate: 45-90 minutes
- Evaluate:45-90 minutes
- Pipets, one per solution (a small test-tube can be taped to the side of the reagent bottle to hold each pipet to prevent the pipets from being contaminated by other reagents).
- 24-well deep well microplates, 9 total if each chemical is used
- 100mL bottle of each of the reagents shown in the table below:
|Cation Source||Anion Source|
|*These chemicals are toxic, and even though they are being used in a small-scale laboratory activity, can be deleted from this activity at the instructor’s discretion without affecting the overall laboratory results.|
- 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.
- SDS and chemical information for the solutions used in this lab can be found here.
- Storage and disposal information can be found here.
- Preparation of Chemicals: Creating the 0.1M solutions could take some time. I suggest utilizing student volunteers if possible to not only give them experience making solutions, but also helping reduce instructor preparation time. Once the stock solutions are prepared, the laboratory investigation preparation times for the actual activity should be 15-30 minutes.
Time can vary depending on how long student groups are given to discuss amongst their group and the depth of the whole group discussion. Use the LINK strategy (List, Inquiry, Notes, Know) as outlined in the steps below.
- Each group will be assigned a color. Colors can be assigned in any way that the teacher thinks would work best for their class.
- Option 1: Have the students choose their favorite color and create groups of students who chose the same favorite color.
- Option 2: Create color cards and have students select their color randomly. Student small teams are formed for those who selected the same color card.
- Begin with the List steps of the LINK strategy. During List, students will surface their prior knowledge about any topic. The students will then share their list with their group and the whole group.
- Students will individually brainstorm everything that they can think of about their color.
- Once students make their brainstorm list, they will get together in their teams and each team member will share one item with their team members. When a student shares the item, if it is on another team member’s list, both students will circle it. If it is not on another team member’s list, the team members can add it.
- When each team member has shared the items on their list and added other team members’ ideas, the team can begin to prepare to share with the large group. Each team will have a spokesperson to share a few ideas with the large group.
- The large group will also have an opportunity to respond to the spokesperson by offering other suggested items not mentioned that the team could add to their list.
- Once their list has been exhausted, then the next team will present. This whole group sharing will continue until each group has had an opportunity to present.
- As the groups are sharing, the teacher could list the items shared on the board, and/or could comment on the items being shared and suggest some inquiry-type questions that could be used in the next section. By making these suggestions, the teacher would actually be modeling the thinking process that will be utilized in the Inquiry section of LINK which would help all levels of students. The amount or depth of questions could be modified depending on the class.
- Next complete the Inquiry steps of the LINK strategy. During Inquiry, students will have their own opportunity to ask an inquiry question—something that they want answered--about their color. When the students begin their research project, this research project will include an inquiry component where teams of students research something that they want answered about a particular color (for instance if your color is red, you could research why ketchup is red). This Inquiry activity will be used to generate the Inquiry question that the students want answered. The Inquiry question will be motivation for the students by providing a purpose for their learning.
- The students individually will list an inquiry question that they want answered about their color.
- The students will then share their inquiry question with their team.
- Once each team member has shared their inquiry question, then the team will prepare another spokesperson to share their Inquiry question with the large group.
- Again, the whole group will have the opportunity to comment offering additional ideas or information that the team may use as they proceed with their investigation.
- The teacher can provide suggestions for narrowing their topic, refining their question, or other suggestions to help the group during their investigation. The amount or depth of questions could be modified depending on the class.
I suggest managing the time for this process by allowing 45-90 minutes for research and another 45-90 minutes for preparing presentations. Students will research the following aspects of their color:
- The history of the color in regards to paint and pigment.
- The discoveries and scientific advancements that have happened throughout history for their color.
- Answers to their inquiry question.
- Students will summarize their research and prepare a presentation of their findings for the Evaluation portion of this lesson.
Using the Student Handout, review the Introduction and Background section with students. This information covers the following topics: Double Displacement reactions, Solubility Rules and Net Ionic Equations. Teachers may find this presentation helpful to use during instruction.
Students will complete a small-scale laboratory investigation. During this investigation, aqueous solutions of various ionic compounds will be mixed to determine which will produce a precipitate. Some precipitates will be colored and some will be white or black.
- Choose the Unknowns from the list of cation sources and anion sources, preferably one that produces lots of precipitates! Best choice for Unknown 1=AgNO3; Unknown 2=NaOH.
- Students should complete the laboratory activity according to the Student Laboratory Activity handout. Teachers may choose to have the students design their own procedure in order to make the laboratory activity more inquiry-based. Include a presentation of the chemical hazards for each of the chemicals to be used in this laboratory activity.
- Evaluate: Students will present the results of their research project on colors. Students will also determine the identity of an unknown and present experimental evidence to support their claim.
- Extend:Students could complete a quantitative analysis of the precipitate production by producing 1gram of precipitate. Students could use stoichiometry to determine how much of each reagent is needed to produce 1 gram of precipitate.