How to Perform a Titration (5 Favorites)

DEMONSTRATION in Concentration, pH, Molarity, Titrations, Indicators. Last updated April 26, 2019.


Summary

In this demonstration, the teacher will show how a titration is set-up and performed. The teacher will utilize different indicators to show how they work and why they are necessary. At the end of the demonstration, the teacher will also explain how to calculate the molarity of the unknown substance.

Grade Level

High School

AP Chemistry Curriculum Framework

This demonstration supports the following learning objectives:

  • Big Idea 1: The chemical elements are fundamental building materials of all matter, and all matter can be understood in terms of arrangements of atoms. These atoms retain their identity in chemical reactions.
    • 1.20 The student can design, and/or interpret data from, an experiment that uses titration to determine the concentration of an analyte in a solution.
  • Big Idea 3: Changes in matter involve the rearrangement and/or reorganization of atoms and/or the transfer of electrons.
    • 3.1 Students can translate among macroscopic observations of change, chemical equations, and particle views.
    • 3.2 The student can translate an observed chemical change into a balanced chemical equation and justify the choice of equation type (molecular, ionic, or net ionic) in terms of utility for the given circumstances.
    • 3.3 The student is able to use stoichiometric calculations to predict the results of performing a reaction in the laboratory and/or to analyze deviations from the expected results.
    • 3.4 The student is able to relate quantities (measured mass of substances, volumes of solutions, or volumes and pressures of gases) to identify stoichiometric relationships for a reaction, including situations involving limiting reactants and situations in which the reaction has not gone to completion.
  • Big Idea 6: Any bond or intermolecular attraction that can be formed can be broken. These two processes are in a dynamic competition, sensitive to initial conditions and external perturbations.
    • 6.13 The student can interpret titration data for monoprotic or polyprotic acids involving titration of a weak or strong acid by a strong base (or a weak or strong base by a strong acid) to determine the concentration of the titrant and the pKa for a weak acid, or the pKb for a weak base.

Objectives

By the end of this demonstration, students should be able to

  • Understand how to set-up the equipment for a titration.
  • Accurately follow the procedural steps to perform a titration.
  • Identify different indicators and explain their purpose.
  • Calculate the molarity of an unknown substance.

Chemistry Topics

This lesson supports students’ understanding of

  • Acids and bases
  • Titrations
  • Indicators
  • pH
  • Molarity

Time

Teacher Preparation: 30- 45 minutes

Lesson: 45 minutes

Materials

  • 4 burets
  • 2 ring stands
  • 2 buret clamps
  • 4 flasks
  • 0.1- 0.25M Hydrochloric acid (~40mL per class)
  • 0.25M Sodium Hydroxide (~50mL per class)
  • Distilled water (~80mL per class)
  • Phenolphthalein
  • Bromothymol Blue
  • Universal Indicator
  • 3 pipets (for the indicator)
  • pH paper
  • Graduated cylinders

Safety

  • Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required
  • When working with acids, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.
  • When working with acids and bases, if any solution gets on your skin immediately rinse the area with water.
  • 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 diluting acids, always add acid to water.

Teacher Notes

  • Prior to doing this demonstration, students should be taught about titrations and indicators, so that they have the necessary background information, and can understand the purpose of the demonstration.
  • I demonstrate and explain the titrations with the indicators added to them first and then discuss the example that does not have an indicator added.
  • Most of the time I don’t need to demonstrate the titration with no indicator added, because they already understand and can predict, based on our discussion, that they won’t be able to see anything happen.
  • The demonstration procedures are included on the student document, so that the student can have the titration procedures for future reference.
  • Students should follow along with the procedures, as given to them on the student document and record the necessary data as each step is demonstrated for them.
  • It might help to label each flask with a number for each titration.
  • For each of these titration it should not take more than 7mL of the base to titrate the acid.
  • Possible answer to conclusion question: The shampoo must have some type of indicator in it, most likely Bromothymol blue. Bromothymol blue is blue when in the presence of a base, and sodium hydroxide is a base. So, as long as there is still relaxer in the woman’s hair the soap from the shampoo will be blue. Once the soap is colorless, that lets the stylist know that all of the relaxer has been washed out.

For the Student

Background

The process of titration will be used to determine the concentration of a solution. At the equivalence point there will be an equal number of moles of H3O+ and OH- ions. We will use various indicators to detect the equivalence point through the observation of a color change. This can easily be determined because the solution will change color at the equivalence point by the addition of a single drop of base. At the equivalence point, or neutralization, the number of moles of acid equals the number of moles of base, if the mole ratio of the balanced equation is one.

Objective

In this demonstration, you will observe how a titration is set-up and performed. Also, you will be able to calculate the molarity of the unknown substance.

Materials

  • Burets
  • Ring Stands
  • Buret Clamps
  • Flasks
  • Hydrochloric acid
  • 0.25M Sodium Hydroxide
  • Distilled water
  • Phenolphthalein
  • Bromothymol Blue
  • Universal Indicator
  • Pipets
  • pH paper

Safety

  • Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required
  • When working with acids, if any solution gets on your skin, immediately alert your teacher and thoroughly flush their skin with water.
  • Wash your hands thoroughly before leaving the lab.
  • When diluting acids, always add acid to water.

Procedure

  1. The burette contains 0.25M NaOH solution.
  2. Record the initial reading of the burette in the data table . This is the NaOH initial.
  3. Measure 20 ml of distilled water to increase the volume for each of the 4 flasks and then measure and add 10 ml of HCl solution to each.
  4. Add 2-3 drops of the phenolphthalein indicator to the flask 1. Use a swirling motion to mix the solutions.
  5. Add 2-3 Drops of Universal Indicator into flask 2. Use a swirling motion to mix the solutions.
  6. Add 2-3 Drops of Brothymol Blue into flask 3. Use a swirling motion to mix the solutions.
  7. No indicator is added to flask 4.
  8. HCl initial is recorded as 0ml and HCl final is recorded as 10ml resulting in a 10ml volume of HCl used.
  9. Obtain a small piece of pH paper and determine the pH of the solution in the flask. Record the pH based on the color change of the paper by checking its color with scale on the container. Record the pH value in the data table as “pH initial.”
  10. Place the flask under the NaOH burette and add the base slowly, drop by drop while swirling the solution.
  11. Watch the solution carefully, when the last drop added causes the solution to change color the titration is close to completion. If the solution changes color, and remains this color after swirling, stop the titration.
  12. Using pH paper, again determine the pH of the solution and record the value in the data table as “pH final.”
  13. Record the final reading from the burette in the data table as “NaOH final.”
  14. Repeat these procedures for each of the examples.

*Note: DO NOT ADD MORE THAN 7 ML of NaOH to ANY of the flasks.

Data

Trial HCl Initial HCl Final Volume HCl NaOH Initial NaOH Final Volume NaOH
(final-initial)
pH Initial pH Final
Phenolphthalein
Indicator
0mL 10mL 10mL
Universal Indicator 0mL 10mL 10mL
Brothymol Blue
Indicator
0mL 10mL 10mL
No Indicator Added (Control) 0mL 10mL 10mL

Calculations

Use the information from the data table and the following equation to calculate the Molarity of the acid.

[Molarity (acid) × Volume (acid) × #of Hydrogens = Molarity (base) × Volume (base) × # of Hydroxides]

Analysis

  1. Are the molarity values that you calculated in a reasonable range? Why or why not?
  2. Which indicator do you think worked the best? Explain why.

Conclusion

A woman went to a salon to get a relaxer put on her hair. Relaxers are made with sodium hydroxide. After washing the relaxer out the stylist needs to shampoo the woman’s hair again. The soap from the shampoo is blue. The stylist shampoos the woman’s hair again, but this time the soap is a little less blue. The stylist shampoos the woman’s hair a third time and this time the soap is colorless. What caused the shampoo to change colors?