Summary

In this activity, students will use a simulation to collect titration data to determine the concentration of a strong acid or a strong base. Multiple practice opportunities exist, as each time the simulation is reset, a new value is generated for the unknown concentration. The simulation is not designed to be used in place of the lab technique, but rather as a way of strengthening the skills already learned in the lab.

Grade Level

High School

NGSS Alignment

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

• HS-PS1-7: Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data
  • Planning and Carrying Out Investigations

Objectives

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

• Use titration data to determine the concentration of an acid or a base.

Chemistry Topics

This simulation supports students’ understanding of:

• Acid base reactions
• Titrations
• pH
• Equivalence Point

Time

Teacher Preparation: 5 minutes (photocopy student handout)

Lesson: 30-50 minutes

Materials

• Student Handout
• Device connected to the internet
• Computer access to https://teachchemistry.org/classroom-resources/acid-base-titration

Safety

• There are no particular safety hazards in this activity.

Teacher Notes

• This simulation can be found at the following link (note that students can access the simulation without an AACT login): https://teachchemistry.org/classroom-resources/acid-base-titration
• Teachers can use the simulation to best meet their needs. For example, it can be integrated into a lecture or review, without using the available student handout, or alternatively, teachers can adapt the student handout, or create their own, to be used in any phase of learning, or for formative assessment.
• This version of the activity is intended for first-year chemistry courses. An AP version of this activity is also available.
  • This activity uses only strong acids and strong bases within the simulation. As pH curves are primarily an AP-level topic, this handout defines “equivalence point” and includes an example graph, along with some leading questions that show how to find the volume at this point.
  • As with a titration performed in the lab, the data points may not perfectly line up with the ideal points on the graph. The simulation allows for some tolerance and students should choose the data point that is closest to the ideal value. In the image below, the red arrow shows the equivalence point. The graph trace, shown with a label, identifies 15.88 mL as the volume of the closest data point to the equivalence point. The next closest traceable volume is 15.87 mL. Students using either of these volumes correctly in their calculation will get a correct concentration value.

• The handout is scaffolded such that Titration #1 guides students to find all required data, while Titration #4 directs them to create their own data tables to decide what data is needed.
  
• Student pre-requisite skills and knowledge:
  • Writing and balancing equations for reactions of acids with bases:
    • What are Acids and Bases? is a video with student questions.
  • Use of the mole ratio and stoichiometry:
    • Acid/Base Stoichiometry allows students to explore stoichiometry by collecting carbon dioxide generated from an acid-base reaction.
  • Lab experience with any form of a titration process, even without the standard equipment (such as microscale processes and dropwise analysis):
    • Titration Curves uses drops from a plastic pipet to teach the titration curve without using a buret.
• This simulation should be used to reinforce titration skills, rather than to replace the lab experiment.
  • For first-year chemistry students, the simulated lab provides a way to practice data analysis and stoichiometry calculations with greater frequency than can be done using only the laboratory method.
• The simulation can be used as many times as needed for additional practice.
  • Each time the simulation is reset, new values are generated for the analyte solution concentration (to be calculated by student and checked for correctness by inputting into the simulation).
  • All 6 substances can be used for determining the concentration of analyte:
    • When the selected analyte is HCl or NaOH, the student chooses the titrant concentration from a pull-down menu. The titrant will automatically be assigned as either NaOH or HCl, accordingly.
    • For the other four analytes (weak acids, HC₂H₃O₂ and unknown HX, and weak bases NH₃ and unknown B), the program will generate a titrant concentration (with either NaOH or HCl) and display it on the screen. For these analytes, equilibrium effects come into play. However, a first-year student can ignore the equilibrium calculations and still use any substance for practicing the concentration calculations. The only difference is that the equivalence points for these analytes will not be at pH=7. The equivalence point can always be determined by finding the point that is closest to the middle of the large pH change.
    • The program permits the student to check answers, even if only the concentration is entered, and will simply display a message that the equilibrium calculation is incorrect when that answer is left blank.

• Students should check answers by entering their values in the answer boxes.
  • If submitted answers are incorrect, hints will be displayed. The students should check their work and re-calculate to see if they can correct their mistakes. To enter a new value, students must push Dismiss after reading the hints. After the second answer, the correct values are displayed. (Student will not be told whether they entered the correct answer at this point, as they can check their answers based on the display.) 
  • There is a Reset button under the titration set-up image at the left of the screen and underneath the answer boxes where students check their answers. Pushing this button will bring the user back to the beginning screen to choose a new substance. With each reset, the random value generation begins anew.