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Acid-Base Titration Simulation

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    282807

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    Learning Objectives:

    • List and describe the factors/parameters that affect the shape of acid-base titration curves
    • Predict and explain why the change occurs when each of these factors/parameters is adjusted
    • Calculate the pH of solution and articulate its correlation to any point on the titration curve
    • Identify the different features on a diprotic acid titration curve

    A. Titration Curve Sketch

    1. Sketch the following two titration curves
      1. pH vs. volume of base added: weak acid (HA) being titrated by a strong base (NaOH)

         

         

         

         

         

         

      2. pH vs. volume of base added: strong acid (HCl) being titrated by a strong base (NaOH)

     

     

     

     

     

     

    1. What species are present at the half-equivalence point for acid HA being titrated with NaOH? At equivalence point?

     

     

     

     

     

    B. Titration curve simulation for Monoprotic Weak Acid/Base:

    Go to the following website:

    https://community.asdlib.org/activelearningmaterials/designing-an-acid-base-titration/

    Click on Investigation #2:  Titration of Monoprotic Weak Acid or Weak Base

    1. Explore the effects of changing 1 variable as you hold the other 3 constant. Start with the following conditions:
      • Choose “weak acid” as analyte
      • Uncheck the box labeled [titrant]=initial [analyte]
      • pKa = 2, initial [analyte]=0.1 M, initial volume = 50 mL, [titrant] = 0.1 M

      As you investigate each variable, keep the following question(s) in mind: What impact does each change have on the shape of the titration curve, the location of the equivalence point, and the change in pH at the equivalence point? And why?

      1. pKa: Increase from 2 to 8.5. Remember to relate the pKa change to the strength of acid here.

         

         

         

      2. initial [analyte]: Change the pKa back to original setting and increase concentration from 0.1  M to 0.15 M.

         

         

         

      3. Initial volume of analyte: Change the initial [analyte] back to original setting and decrease initial volume of analyte from 50 mL to 25 mL.

         

         

         

      4. [titrant]: Change the initial volume of analyte back to original setting, and increase [titrant] from 0.1 to 0.2 M.

     

     

    1. Switch from “weak acid” to “weak base” on the simulation. Note any changes in the titration curve.

     

     

     

     

     

     
    1. One gram of weak base, B (MW = 100 g/mol, pKb = 5.42) is dissolved in 50 mL water. The resulting solution is titrated with 0.2 M HCl.

      Step#1: total of 15 mL of HCl was added

      Step#2: total of 25 mL of HCl was added

      Step#3: total of 50 mL of HCl was added

      1. What are the numerical values that you would input as your 4 variables in the simulation (e.g., analyte concentration)? Update the conditions in your simulation

         

         

         

         

      2. Approximate the pH for each step using the simulated titration curve

         

        Step #1: ______

         

         

        Step #2: ______

         

         

        Step #3: ______

         

         

      3. Identify the major species at each step (B= weak base, BH+=conjugate acid) and explain how you identified them

         

        Step #1:

         

         

        Step #2:

         

         

         

        Step #3:

         

         

         

         
      4. Calculate the pH for each step using an ICE table or the Henderson-Hasselbach equation and confirm your calculated value with the estimated values from part (b)

         

        Step #1:

         

         

         

         

         

        Step #2:

         

         

         

         

        Step #3:

     

     

     

     

     

     

    C. Titration curve simulation for Diprotic Weak Acid/Base:

    Click on Investigation #3: Titration of Diprotic Weak Acid or Weak Base

    In next week’s titration lab of an unknown diprotic acid, you will use 0.15 M NaOH to titrate the unknown acids. You will prepare approximately 25 mL of 0.10 M of the unknown acid. There are 4 possibilities of acids and their assigned Ka1 and Ka2 values according to the table below.

    1. Using the conditions given to input the numerical values into the simulation of Investigation #3, sketch the titration curves of each potential unknown acid, mark “x” where end points are, and circle the buffering regions. Note any differences in features between each curve.

      Table 1. List of Potential Unknown Diprotic Acids

      Potential Acid

      Ka1

      Ka2

      Ascorbic acid

      7.9 x 10-5

      1.6 x 10-12

      Glycine HCl

      4.5 x 10-3

      1.7 x 10-10

      Maleic acid

      1.5 x 10-2

      8.5 x 10-7

      Oxalic acid

      5.9 x 10-2

      6.5 x 10-5

       

      1. Ascorbic Acid

         

         

         

         

         

         

         

         

         

         

      2. Glycine HCl

         

         

         

         

         

         

         

         
      3. Maleic Acid

         

         

         

         

         

         

         

      4. Oxalic Acid

     

     

     

     

     

     

     

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