1 / 11

Acid-Base Titrations

Acid-Base Titrations. End point and equivalence point Calculating the concentration of unknown acid or base Choosing an indicator dye Titration of a strong acid by a strong base Titration of a weak acid by a strong base

fallon
Download Presentation

Acid-Base Titrations

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Acid-Base Titrations End point and equivalence point Calculating the concentration of unknown acid or base Choosing an indicator dye Titration of a strong acid by a strong base Titration of a weak acid by a strong base Calculation of the titration curve - buffer region of a titration curve Dependence of titration curve on pKa Using the H-H equation to calculate pH

  2. Acid-Base Titrations pH At the equivalence point, mol H+ = mol OH- strong base titrated with strong acid strong acid titrated with strong base

  3. Titrations - Determination of the concentration of an unknown acid or base A burette is used to add a precise volume of acid (or base) to the unknown solution. At the end-point of the reaction, the indicator changes color. 1. The flask contains the unknown acid 2. Base is added drop by drop to the end-point. 3. The indicator (in this case phenolphthalein) turns pink at the end-point.

  4. Example: 0.231 M HCl titrates 50.00 mL unknown base. 45.27 mL HCl is added at the equivalence point. (Molarity * Volume)acid=(Molarity * Volume)base [base] = ( 0.321 M * 0.04527 L )/ .05000 L = 0.291 M Calculating the Concentration of an Unknown Acid or Base end point: indicator changes color equivalence point: moles [H+] = moles [OH-] When the indicator is properly chosen: - end point = equivalence point within experimental error.

  5. The Common Indicator Dyes

  6. pH = pKa + log10 [base] [acid] Titration of a Weak Acid with a Strong Base CH3COOH = CH3COO- + H+ pKa = 4.75 When pH = 4.75, [CH3COOH] = [CH3COO-] This is the center of the buffering region.

  7. pH = pKa + log10 [base] [acid] Exercises: Calculate the Titration Profile What is the pH when 90.0 mL of NaOH has been added? Ans: 5.70 What is the pH when 30.0 mL of NaOH has been added? Ans: 4.38

  8. Dependence of the Titration Curve on Acid Strength On this diagram, note that the pH = pKa at the midpoint of the buffering region for each weak acid.

  9. pH = pKa + log10 [base] [acid] Titration of a Weak Base by a Strong Acid NH4+ = NH3 + H+ pKa = 9.25 When pH = 9.25, [NH4+] = [NH3]

  10. Problem (a) Calculate the pH of a 500 mL solution prepared from: 0.050 mol of acetic acid and 0.020 mol sodium acetate. HAc = H+ + Ac- pKa= 4.75 0.020 / 0.50 [Ac-] pH = pKa + log10 [HAc] 4.75 0.050 / 0.50 pH = 4.35

  11. Problem 10.45 (2) Suppose that 0.010 mol NaOH is added to the buffer of part (a). What is the pH? (b) HAc + OH- = H2O + Ac- pKa = 4.75 (0.020 + 0.010) / 0.50 [Ac-] pH = pKa + log10 [HAc] (0.050 - 0.010) / 0.50 4.75 4.63 As long as the buffer capacity is not exceeded, the change of pH is small, in this case, 4.35 to 4.63

More Related