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LAB in Titrations, Indicators, Strong vs Weak, pH, Equivalence Point, Unlocked Resources. Last updated October 08, 2019.

Summary

In this lab, students will use their background with titrations to see how different indicators change colors at different pHs.

Grade Level

High school

Objectives

By the end of this lesson, students will know

  • How certain indicators are better choices for different partnerships of strong/weak acid/bases in a titration.

Chemistry Topics

This lesson supports students’ understanding of

  • Titrations
  • Indicators
  • Strong vs. weak acids/bases

Time

Teacher Preparation: 30 minutes

Lesson: 1.5 hours

Materials

For each group:

  • HCl (some 1.0 M, some 0.1 M—dilute 1.0 M)
  • NaOH (approx 0.1 M)
  • HC2H3O2 (various concentrations)
  • NH3 (2 M—MUST dilute to 0.1 M if you need it)
  • A couple other weak acids and maybe a base
  • Titration equipment
  • Possible indicators:
    1. thymol blue
    2. thymolphthalein
    3. bromthymol blue
    4. bromphenol blue
    5. congo red
    6. phenol red
    7. phenophthalein
    8. bromcresol green
    9. alizarin yellow
    10. cresol purple
    11. methyl orange
    12. methyl red
    13. fluorescein
    14. universal
    15. bromcresol green
    16. fuchsin, basic
    17. thymol blue

Safety

  • Always wear safety goggles when working with chemicals in a lab setting.
  • 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.
  • 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

This activity is engaging, and a challenging topic in additional aspects of equilibrium. Brought back to "real life" with technology and some nice colors.

For the Student

Lesson

Background

Watch how to do a titration. Don’t just watch, pay attention. Take notes and rewatch parts of the video. You do not have a photographic memory.

Listen.

They’ll tell you how to mess it all up and/or fix it. Take your iPad with the video into the lab as you setup. Rewatch if you don’t remember parts.

Materials

  • HCl (some 1.0 M, some 0.1 M—dilute 1.0 M)
  • NaOH (approx 0.1 M)
  • HC2H3O2 (various concentrations)
  • NH3 (2 M—MUST dilute to 0.1 M if you need it)
  • A couple other weak acids and maybe a base
  • Titration equipment
  • Possible indicators:
    1. thymol blue
    2. thymolphthalein
    3. bromthymol blue
    4. bromphenol blue
    5. congo red
    6. phenol red
    7. phenophthalein
    8. bromcresol green
    9. alizarin yellow
    10. cresol purple
    11. methyl orange
    12. methyl red
    13. fluorescein
    14. universal
    15. bromcresol green
    16. fuchsin, basic
    17. thymol blue

Method

You will be assigned an indicator. You can choose from the materials to carry out a titration with your assigned indicator. Research what you want: use Google, your book, notes. You must perform a titration and collect titration curve data and use your indicator to attempt to “indicate” the equivalence point of the titration curve. Your indicator may not work perfectly to “indicate” the equivalence point, and that is alright, as long as you note and report this. You must take picture(s) of you performing this activity and prepare a 1.0 minute verbal presentation.

Data

At the end of the experiment you should have:

  1. a titration curve you create. Provide a picture of this in full color.
  2. handwritten notes and a sketch of the titration curve
  3. other supporting evidence ­ pictures, screenshots, websites, etc.
  4. a presentation. You can:
    • use Google presentation
    • use a video tool
    • use iShowU
    • use Screen­Chomp
    • use some other tech tool

but if you don’t know how to use any of these technology tools, just take pictures with your iPad and show them and show your handwritten pages on the document camera.

Conclusion

You will share your findings with the class in a 1-minute presentation.

  1. Introduce your new friend (the indicator) by name and chemical formula.
  2. When does your indicator friend change (pH) and what colors does s/he produce ­ pictures are nice, but not required.
  3. What type of titration is your indicator good for (e.g., strong acid/ strong base, weak acid/strong base, etc.). Justify your selection. Use chemistry words. Justify your selection. Explain, in 30­seconds of immense detail.
  4. At least five pictures of you and your real­life friend with the titration curve you created. An iPad picture is fine, but make sure you visually SHOW where the indicator “indicates” the equivalence point on a computer­collected titration curve. POINT (literally or digitally) to this point in the picture and on the titration curve.
  5. 10–15 seconds on “what makes up my new indicator friend” (e.g., chemical structure, a Lewis dot picture of s/he, what makes them “indicate,” maybe some of the indicator’s chemical relatives, etc.).