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In this lab, students will identify 3 unknown acids by using the solubility rules. They will be given a list of materials and will design their own procedures for identifying the unknowns. For each combination of reactants, they will predict whether a product forms and, if it does, write complete and net ionic equations for those reactions.

Grade Level

High School

NGSS Alignment

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

  • 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.
  • Scientific and Engineering Practices:
    • Analyzing and Interpreting Data
    • Planning and Carrying Out Investigations
    • Constructing Explanations and Designing Solutions


By the end of this lab, students should be able to:

  • Identify 3 unknown acids as either hydrochloric acid, acetic acid, or sulfuric acid.
  • Use solubility rules to determine if a precipitate is expected.
  • Write complete and net ionic equations.

Chemistry Topics

This lab supports students’ understanding of:

  • Experimental design
  • Chemical reactions
  • Solubility Rules
  • Double Replacement reactions
  • Complete and net ionic equations


Teacher Preparation: 20 minutes
Lesson: 40 minutes

Materials (per lab group)


  • 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
  • When working with acids, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.
  • When diluting acids, always add acid to water.

Teacher Notes

  • This lab is designed to be performed after instruction on chemical reactions, double replacement reactions, solubility rules, complete ionic equations, and net ionic equations.
  • The SDS information for all of the substances used in this lab are linked in the materials list, above. Of particular note are the sulfuric and hydrochloric acids, which are both strong acids, so even though they are not particularly concentrated at 1 M, they have very low pH values and students should be instructed to be extremely cautious when handling their acid samples. (Flinn even notes “Treat all sulfuric acid solutions with the same caution you would have for concentrated sulfuric acid. For example, the pH of 0.05 M sulfuric acid solution is 1.2.”)
  • Additionally, depending on your state/local waste disposal requirements, you may need to dispose of the lead- and barium-containing products as hazardous waste using a licensed hazardous waste disposal firm. See Flinn’s Disposal Methods #26c, #27f, and #27h, and always consult your local authorities before disposing of lead or barium compounds in the trash or down the sink. To minimize hazardous waste products, use the smallest amounts of reagents possible.
  • Students can be in groups of 2 or 3.
  • Students can use a large classroom solubility table or individual ones. Solubility rules can be found in most chemistry textbooks in the form of a table or chart, such as this one.
  • If multiple classes will be reusing the well plates, be sure students thoroughly rinse them with lots of water when they are done. If there are still some leftover ions in the wells from the previous group, it could cause contamination for the next lab group which would result in more precipitates than expected.
  • This lab requires students to design their own procedures for determining the identities of the unknown acids, which, even for a fairly simple experiment like this one, can be very challenging for students if they are used to being told exactly what to do. It may take longer than you expect, but it is a very valuable scientific skill to develop! If you have lower-level classes or wish to focus more on the data analysis aspect of this lab, students can be given the following instructions and data table if they struggle to develop their own procedures:
    • Place 5 drops of each unknown acid in 2 wells on the well plate.
    • Place 5 drops of lead (II) nitrate solution with each unknown acid.
    • Place 5 drops of barium nitrate solution with each unknown acid.
    • Record which reactions form a precipitate and which ones do not form a precipitate.

Precipitate formed
(yes or no)
Unknown Acid A + lead (II) nitrate
Unknown Acid A + barium nitrate
Unknown Acid B + lead (II) nitrate
Unknown Acid B + barium nitrate
Unknown Acid C + lead (II) nitrate
Unknown Acid C + barium nitrate

For the Student



I need your help! I was organizing the acids in the chemical storage room and relabeling the acids because the old labels were getting hard to read. I took the old labels off 3 different acids and got them mixed up before I put on the new labels. I know this was a big mistake and should have never happened! Luckily, I know the 3 acids were hydrochloric acid, sulfuric acid, and acetic acid. With your knowledge of double replacement reactions and the solubility rules, I think you can figure out which acid is which.

In this lab, you will have small samples of all three acids. The acids are labeled Unknown A, Unknown B, and Unknown C. Each is the same concentration. Your goal is to identify which one is hydrochloric acid, which is sulfuric acid, and which is acetic acid using lead (II) nitrate and barium nitrate.

Prelab Questions

  1. What evidence is proof of a double replacement reaction?
  2. What is a complete ionic equation?
  3. What are spectator ions?
  4. What is a net ionic equation?


Identify the 3 unknown acids using lead (II) nitrate and barium nitrate


  • 10 mL of Unknown Acid A, Unknown Acid B, and Unknown Acid C
  • 10 mL of 0.20 M lead (II) nitrate
  • 10 mL of 0.50 M barium nitrate
  • Well plate
  • Disposable pipettes
  • Periodic table and solubility rules table


  • Always wear safety goggles when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.
  • When working with acids and bases, if any solution gets on your skin immediately rinse the area with water.
  • When diluting acids, always add acid to water.


  • Using the materials supplied, create steps to accomplish the goal of identifying the unknown acids.
  • Write out the steps to your procedure in the space below and get approval from the instructor before performing any reactions. (Be sure your steps are clear and could be easily followed by someone unfamiliar with the experiment!)
  • Create a data table to show your results.



  1. Write out all possible reactions between the 3 acids and the testing solutions of lead (II) nitrate and barium nitrate. Write the products expected along with the state of matter of the products and reactants. Write “No reaction” if you don’t expect to see a reaction between those two solutions.
  2. Identify the unknown acids A, B, and C. Provide reasoning by using your data and the equations as evidence.
  3. Write the complete and net ionic equations for each reaction that produced a precipitate.
  4. A precipitation reaction used in industry for a medical application is the formation of barium sulfate from barium chloride and sodium sulfate. Soluble barium salts are toxic, but barium sulfate is so insoluble that it can be used to diagnose stomach and intestinal problems without being absorbed into tissues. The barium sulfate will show on an X-ray of a patient that has been given a “barium milkshake” – a suspension of very fine barium sulfate particles in water. Write out the reaction between barium chloride and sodium sulfate to produce barium sulfate. Write the complete and net ionic equation.