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LAB in Solubility, Chemical Change, Precipitate, Net Ionic Equation, Balancing Equations, Chemical Change, Solubility Rules. Last updated August 19, 2019.

Summary

In this lab, students will mix ionic solutions to determine what combinations form precipitates. By knowing the ions present, and by knowing solubility rules, they will be able to deduce which ions are responsible for the precipitate and write overall equations and net ionic equations.

Grade Level

High school

AP Chemistry Curriculum Framework

This laboratory experiment supports the following units, topics and learning objectives.

  • Unit 3: Intermolecular Forces and Solubility
    • Topic 3.10: Solubility
      • SPQ-3.C: Explain the relationship between the solubility of ionic and molecular compounds in aqueous and nonaqueous solvents, and the intermolecular interactions between particles.
  • Unit 4: Chemical Reactions
    • Topic 4.1: Introduction for Reactions
      • TRA-1.A: Identify evidence of chemical and physical changes in matter.
    • Topic 4.2: Net Ionic Equations
      • TRA-1.B: Represent changes in matter with a balanced chemical or net ionic equation: a. For physical changes. b. For given information about the identity of the reactants and/or product. c. For ions in a given chemical reaction.
    • Topic 4.7: Types of Reactions
      • TRA-2.A: Identify a reaction as acid-base, oxidation-reduction, or precipitation.

Objectives

  • Have students perform a microscale lab to identify chemical reactions.
  • Once a reaction is identified as occurring, students write overall ionic and net ionic equations.

Chemistry Topics

This lesson supports students’ understanding of

  • Net ionic equations
  • Solubility rules
  • Chemical changes

Time

Teacher Preparation: 1 hour

Lesson: 1 class period

Materials

For each group:

  • Poly film with grid markings
  • White paper
  • Pipets with the following solutions:
    • Co(NO3)2(aq)
    • NaNO3(aq)
    • KOH(aq)
    • NaOH(aq)
    • CoCl2(aq)
    • FeCl3(aq)
    • Cu(NO3)2(aq)
    • Pb(NO3)2(aq)

Safety

  • Always wear safety goggles when working with chemicals.
  • If any solution gets on students’ skin, they should alert you and thoroughly flush their skin with water immediately. Some of these compounds are considered skin irritants.
  • Co(NO3)2 is considered hazardous but has educational utility. If you don’t have access to it, you can omit it or substitute with Fe(NO3)3 (results will differ for these reactions from the answer key in the PowerPoint).
  • 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.

Teacher Notes

  • Chemical use is minimal and once mixed can be used for several years.
  • Great practice for writing and balancing chemical equations.
  • Answers to Prelab questions are in the PowerPoitn (slide #5)
  • There should be 12 reactions that result in a precipitate. In the PowerPoint, the 12 reactions with the net ionic equations are shown (slide #6 & slide #7).

For the Student

Lesson

Background

Many ionic solids dissolve in water to form clear, aqueous solutions that conduct electricity. It is the ions in solution that conduct an electric current. These solutions contain both positive ions (cations) and negative ions (anoins) in such a ratio that the net electric charge of the solution is zero.

KCl (s) dissolved in H2O ⇾ K+ (aq) + Cl- (aq)
CaCl2 (s) dissolved in H2O ⇾ Ca2+ (aq) + 2 Cl- (aq)

In this experiment, you will mix various ionic solutions, two at a time, and will determine which new combinations of ions will form precipitates (solids that do not dissolve). By knowing the ions present, and by understanding solubility rules, you will be able to deduce which ions are responsible for the precipitate. You will also write overall reaction equations and net ionic equations.

Example

Suppose you have two aqueous solutions. One was prepared with Pb(NO3)2 (s), and the other was prepared with NaCl (s). Both solids dissolve in water and the solutions contain no visible solids; they are clear. The ions in each solution are:

Pb(NO3)2 (s) dissolved in H2O ⇾ Pb2+ (aq) + 2 NO3- (aq)
NaCl (s) dissolved in H2O ⇾ Na+ (aq) + Cl- (aq)

When the solutions are mixed, a precipitate is observed. Two of the four ions have combined to form a precipitate. The original combinations, that is Pb2+ (aq) + 2 NO3- (aq) AND Na+ (aq) + Cl- (aq), are NOT responsible for the precipitate because before the reaction there was no solid. The new possible combinations of ions are:

Pb2+(aq) + Cl-(aq) and Na+(aq) + NO3-(aq)

Of these, you can see from the solubility rules that the combination Pb2+(aq) + Cl-(aq) will form a precipitate, while Na+(aq) + NO3-(aq) will remain as ions in the solution.

It is necessary now to write an overall reaction equation to show what happens in this reaction. Remember, both atoms and charges must be conserved when writing a chemical reaction. The overall reaction equation is:

Pb2+(aq) + 2 Cl-(aq) + 2 Na+(aq) + 2 NO3-(aq) ⇾ PbCl2(s) + 2 Na+(aq) + 2 NO3-(aq)

After writing this overall reaction equation, it is easy to see that the Na+(aq) and NO3-(aq) ions did not react, but merely stayed in solution. Such ions are called spectator ions. In a net ionic equation, the spectator ions are omitted.

Pb2+(aq) + 2 Cl-(aq) ⇾ PbCl2(s)

Prelab Questions

  1. What ions are present in the following solutions?

NaCl (aq) ⇾ ____________________
AgNO3 (aq) ⇾ ____________________

  1. When these solutions are mixed together, a precipitate is observed. What are the new combinations of ions that could form the precipitate?
    ____________________ and ____________________
  2. Using solubility rules, which new combination will form a precipitate?
  3. Which new combination will remain in solution?
  4. Write the overall reaction equation for this reaction. Be sure to indicate the correct state for each reactant and each product.
  5. Write the net ionic equation for this reaction. Again, include the states.
  6. Explain why you would expect no reaction between solutions of KOH(aq) and NaOH(aq).

Purpose

You will mix ionic solutions and determine what combination of ions form a precipitate. You will write overall reaction equations and net ionic equations to explain these reactions.

Safety

Observe normal lab precautions. Wear goggles. Do NOT touch your mouth, eyes, or face with your hands, and be sure to wash your hands when you have cleaned up your lab area.

Materials

  • One piece of poly film with grid markings
  • One set of eight different solutions in droppers

Procedure

  1. Place a white sheet of paper under the poly film to better see the reactions.
  2. Place one drop of the each of the solutions in the proper boxes on your clean piece of poly film as demonstrated by your teacher. DO NOT touch the tip of the dropper to the film or to any chemical. Keep each cap with its appropriate dropper.
  3. Continue in this fashion until all combinations have been tested.
  4. When done, examine your film. On your data table, write PPT for any reactions that resulted in a precipitate. In the boxes in which no precipitate is visible, write NR, meaning “no reaction.”
  5. Rinse the poly film with water and put the film between two paper towels. Do not wipe the poly film, as this will tend to make the Data Table come off the film. Put all lab materials back in their proper places.

Analysis

For each of the PPT reactions:

  1. In the blanks on the right, write the new combinations of ions that could form.
  2. Balance the equations.
  3. Indicate states for each product. [See PowerPoint for the 12 reactions that result with PPT]

1. ___ Co(NO3)2(aq) + ___ NaNO3(aq) ⇾ ____________ + ____________

2. ___ Co(NO3)2(aq) + ___ KOH(aq) ⇾ ____________ + ____________

3. ___ Co(NO3)2(aq) + ___ NaOH(aq) ⇾ ____________ + ____________

4. ___ Co(NO3)2(aq) + ___ CoCl2(aq) ⇾ ____________ + ____________

5. ___ Co(NO3)2(aq) + ___ FeCl3(aq) ⇾ ____________ + ____________

6. ___ Co(NO3)2(aq) + ___ Cu(NO3)2(aq) ⇾ __________ + ____________

7. ___ Co(NO3)2(aq) + ___ Pb(NO3)2(aq) ⇾ ____________ + _____________

8. ___ Pb(NO3)2(aq) + ___ NaNO3(aq) ⇾ ____________ + ____________

9. ___ Pb(NO3)2(aq) + ___ KOH(aq) ⇾ ____________ + ____________

10. ___ Pb(NO3)2(aq) + ___ NaOH(aq) ⇾ ____________ + ____________

11. ___ Pb(NO3)2(aq) + ___ CoCl2(aq) ⇾ ____________ + ____________

12. ___ Pb(NO3)2(aq) + ___ FeCl3(aq) ⇾ ____________ + ____________

13. ___ Pb(NO3)2(aq) + ___ Cu(NO3)2(aq) ⇾ __________ + ____________

14. ___ Cu(NO3)2(aq) + ___ NaNO3(aq) ⇾ ____________ + ____________

15. ___ Cu(NO3)2(aq) + ___ KOH(aq) ⇾ ____________ + ____________

16. ___ Cu(NO3)2(aq) + ___ NaOH(aq) ⇾ ____________ + ____________

17. ___ Cu(NO3)2(aq) + ___ CoCl2(aq) ⇾ ____________ + ____________

18. ___ Cu(NO3)2(aq) + ___ FeCl3(aq) ⇾ ____________ + ____________

19. ___ FeCl3(aq) + ___ NaNO3(aq) ⇾ ____________ + ____________

20. ___ FeCl3(aq) + ___ KOH(aq) ⇾ ____________ + ____________

21. ___ FeCl3(aq) + ___ NaOH(aq) ⇾ ____________ + ____________

22. ___ FeCl3(aq) + ___ CoCl2(aq) ⇾ ____________ + ____________

23. ___ CoCl2(aq) + ___ NaNO3(aq) ⇾ ____________ + ____________

24. ___ CoCl2(aq) + ___ KOH(aq) ⇾ ____________ + ____________

25. ___ CoCl2(aq) + ___ NaOH(aq) ⇾ ____________ + ____________

26. ___ NaOH(aq) + ___ NaNO3(aq) ⇾ ____________ + ____________

27. ___ NaOH(aq) + ___ KOH(aq) ⇾ ____________ + ____________

28. ___ KOH(aq) + ___ NaNO3(aq) ⇾ ____________ + ____________

For each reaction with a PPT, write the overall equation and the net ionic equation. Include the state for each component in both reactions.

Reaction
No. Overall Reaction Equation:
_______
Net Ionic Equation:

Reaction
No. Overall Reaction Equation:
_______
Net Ionic Equation:

Reaction
No. Overall Reaction Equation:
_______
Net Ionic Equation:

Reaction
No. Overall Reaction Equation:
_______
Net Ionic Equation:

Reaction
No. Overall Reaction Equation:
_______
Net Ionic Equation:

Reaction
No. Overall Reaction Equation:
_______
Net Ionic Equation:

Reaction
No. Overall Reaction Equation:
_______
Net Ionic Equation:

Reaction
No. Overall Reaction Equation:
_______
Net Ionic Equation: