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Titration Lab with Kinetics (4 Favorites)

LAB in Significant Figures, Titrations, Strong vs Weak. Last updated April 26, 2019.


Summary

In this lab, students calculate the molarity of an unknown using a titration and also by solving for a dilution.

Grade Level

High school

AP Chemistry Curriculum Framework

Choose the Big Idea associated with this Lesson Plan:

  • Big Idea 1: The chemical elements are fundamental building materials of 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.
    • 3.2 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.
    • 3.4 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.
    • 6.15 The student can identify a given solution as containing a mixture of strong acids and/or bases and calculate or estimate the pH (and concentrations of all chemical species) in the resulting solution.
    • 6.16 The student can identify a given solution as being the solution of a monoprotic weak acid or base (including salts in which one ion is a weak acid or base), calculate the pH and concentration of all species in the solution, and/ or infer the relative strengths of the weak acids or bases from given equilibrium concentrations.

Objectives

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

  • Calculate the molarity of an unknown solution using a titration.
  • Calculate reaction rates.
  • Calculate the amount of a substance required to produce a particular concentration of solution.

Chemistry Topics

This lesson supports students’ understanding of

  • Titration
  • Significant figures
  • Molarity
  • Solutions
  • Reaction rate
  • Kinetics

Time

Teacher Preparation: 30 minutes
Lesson
: 1 hour

Materials

  • Safety glasses
  • Lab apron
  • Unknown [HCl]
  • Known [NaOH]
  • Phenolphthalein
  • Burette
  • 500-mL volumetric flask
  • 250-mL beaker
  • Funnel

Safety

  • Always wear safety goggles and a lab apron to protect your eyes and clothing.
  • When diluting acid, always add acid to water.
  • When working with acids and bases, if any solution gets on your skin immediately rinse the area with water.
  • Students should carefully read the labels and follow the precautions on all containers of chemicals that they use.
  • Students should not taste any chemicals or items used in the laboratory.
  • Students shouldn’t return leftovers to their original container; they should take small amounts to avoid wasting supplies.
  • 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
  • Demonstrate proper use of the burette prior to having students complete the lab.
  • Reinforce the importance of titrating slowly.
  • Students should also have background knowledge of reaction rates prior to the lab.

Teacher Notes

  • Dilute 76 mL of 12-M HCl to 1 L (0.912-M HCl solution)
  • Demonstrate proper use of the buret prior to having students complete the lab.
  • Reinforce the importance of titrating slowly.
  • Students should also have background knowledge of reaction rates prior to the lab.

For the Student

Lesson

Background

Titration is the name given to the process for determining the volume of solution needed to react with a given volume (or mass) of a sample. You will use this process to study quantitatively the reaction between an acid and a base. A common neutralization reaction is the one between the hydrogen ion of an acid and the hydroxide ion of a base to form water:

Acid + Base ⇾ Salt + Water

An indicator solution is used to determine when an acid has exactly neutralized a base. A suitable indicator changes color when equivalent moles of hydrogen ions and hydroxide ions have reacted, this is termed the equivalence point of the titration. That is, [H+] = [OH-] at the equivalence point.

Purpose

Your job in this lab is to correctly determine the molarity (concentration) of HCl by titrating it with sodium hydroxide (NaOH) of known concentration. Then, you will calculate the reaction rate

Materials

  • Safety glasses
  • Lab apron
  • Unknown [HCl]
  • Known [NaOH]
  • Phenolphthalein
  • Burette
  • 500-mL volumetric flask
  • 250-mL beaker
  • Funnel

Safety

  • Always wear safety goggles and a lab apron to protect your eyes and clothing.
  • If you get a chemical in your eyes, immediately flush the chemical out at the eyewash station while alerting the teacher.
  • Do not touch any chemicals with your bare hands.If you get a chemical on your skin or clothing, wash the chemical off at the sink while alerting the teacher. Make sure you carefully read the labels and follow the precautions on all containers of chemicals that you use.
  • Do not taste any chemicals or items used in the laboratory.
  • Never return leftovers to their original container; take only small amounts to avoid wasting supplies.

Prelab Questions

  1. What type of reaction will be taking place in this titration lab?
  2. What is meant by the term “equivalence point”?
  3. Write the balanced equation for the reaction in this titration. Identify the acid, base and salt.
  4. You will be adding the indicator phenolphthalein to the HCl in your flask.
    a. What color will the solution in your flask be before you start adding base?
    b. What color will the solution turn when you have added enough base?
  5. Record the volume of each of the burettes below to the correct number of significant figures.

Procedure

  1. Obtain about 100-mL NaOH solution. Check the label to see what concentration the NaOH solution is. Record this concentration in your Data Table.
  2. Obtain a burette and prepare it for use. This involves the following procedures:
    1. Close the stopcock (valve at the bottom of burette).
    2. Rinse the burette with the NaOH solution.
    3. Fill the burette with the NaOH solution you prepared.
    4. Fill the tip of the burette by allowing several milliliters of solution to run from the burette into a waste beaker. This removes air bubbles.
    5. Read the starting volume graduation (record this starting volume of your Data Table) on the side of the burette. Notice that the burette volumes increase as you progress DOWN the burette.
  3. Using a clean, dry graduated cylinder, measure 40 mL of your HCl solution (of unknown concentration) and pour into a clean, dry 250-mL Erlenmeyer flask.
  4. Add two-three drops of phenolphthalein indicator to your acid solution.
  5. Deliver about one mL of the base solution from your burette into the flask containing the acid and indicator.
  6. Swirl the container and add another one mL of base.
  7. As you continue the adding and swirling, you will notice that a pink color appears in the solution and then disappears after swirling. Finally after several repetitions of this process the pink color will remain. Read and record in your Data Table the burette volume at this equivalence point.
  8. Subtract your "reading before titration" from your "reading after titration" to obtain the approximate volume of base used. You have now completed your "practice or approximation" trial.
  9. Empty the contents of your flask into the sink. Rinse the container with water.
  10. Repeat your titration. Since you have the volume required in your "practice" trial, you can quickly titrate to within about three-four mL of that volume. Now add the base more slowly - a drop per second is a desirable rate - with constant swirling. As the color begins to persist, slow the rate to a drop every 10-15 seconds. Finally as you are very close to the equivalence point, add the base one drop at a time, opening and closing the valve for each drop. An exact equivalence point (your goal) occurs when the solution is still colorless, and 1 additional drop causes the solution to turn a FAINT pink when swirled and then remain pink for at least 30 seconds.
  11. Do at least three trials where you stop at the exact equivalence point. With good technique and careful work, you can obtain 3 trials in which the variation in volume of base used is 0.5 mL or less.
  12. Cleanup Procedure: To clean the burette, drain all remaining NaOH solution from the burette. Complete two water rinses by closing the stop cock and filling the burette with tap water, and then draining this water. Complete a water rinse with about 20 mL of distilled water and the stop cock open.

Results/Observations

Concentration of NaOH (MB)

M

Volume of HCl

(VA)

mL

Trial

Initial Volume Reading

Final Volume Reading

Volume Change (VB)
(Final – Initial)

Practice/Approximation

1

2

3

Calculations

1. Calculate the volume change of base in each trial. (This should be done in the right-most column in your data table above.
2. Given that you know the acid volume, the base concentration, and the volume change of the base for each trial, calculate the molarity of the acid using the titration equation MAVA= MBVB. Show all work.

Trial 1

Trial 2

Trial 3

3. Average each of the molarities you calculated for in problem 2. This is your experimental value.
4. Figure out the accepted value for the concentration of acid by calculating a dilution. The HCl label says 76 mL of 12-M HCl was diluted to 1 L.
5. Calculate your percent error. ((accepted value – experimental value) / accepted value ) x 100 %
6. What volume of 6.0-M HCl is needed to neutralize 2.0 L of 0.10-M NaOH? Show all work.
7. Describe why you wanted the solution to be a pale pink color when the titration was over rather than a dark pink. Hint: When does phenolphthalein turn pink? How does that range relate to the equivalence point?
8. When a substance is considered to be neutral, what is its pH? ______________
9. Now that you know the concentrations of your reactants in the neutralization equation, calculate the reaction rate. First, write the rate law for the reaction if both reactants are first order. Then, calculate the rate using your experimental HCl concentration and the given NaOH concentration. (Let’s say k=1.2 x 10-5 s-1)
10. What is the overall reaction order in this rate law? ______________