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Analysis of Vinegar by Titration

Analysis of Vinegar by Titration . Lab 4. Outline. Purpose Potentiometric Titrations Proticity Equivalence pK a Vinegar Titration Safety Concerns Waste Next Lab Reminder. Purpose.

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Analysis of Vinegar by Titration

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  1. Analysis of Vinegar by Titration Lab 4

  2. Outline • Purpose • Potentiometric Titrations • Proticity • Equivalence • pKa • Vinegar Titration • Safety Concerns • Waste • Next Lab Reminder

  3. Purpose Students will use a pH probe to perform potentiometric titrations to determine the mass percent of acetic acid in vinegar and the pKa of acetic acid.

  4. Potentiometric Titrations • Potentiometric titrations can be used to determine: • proticity (how many acidic hydrogens are donated to solution) • the amount or concentration of acid or base present (using MaVa= MbVb) • pKa (the “– log” of the acid dissociation constant)

  5. Proticity Acetic acid is a monoprotic weak acid that reacts with NaOH or KOH in a 1:1 ratio and produces a single sigmoidal curve.

  6. Equivalence The equivalence point volume is determined by plotting a derivative curve of the titration curve. The steepest point on the derivative curve corresponds to the equivalence point volume. (Find the exact value on your spreadsheet!)

  7. Equivalence Point Volume • The concentration of acetic acid can be determined from: • the equivalence point volume of the base • the concentration of the base • the volume of the acid used in the titration • The equation to use is: • MaVa = MbVb

  8. pKa The pKa of acetic acid is the pH at the half-equivalence point volume of the titration, because: For a weak acid: HA H+ + A- and Ka = At the half-equivalence point, half the acid has been converted to its salt, so: [HA] = [A-] Ka = [H+] pKa = pH

  9. Vinegar Titration • Make the required dilution of vinegar. • Calibrate your pH probe. • Titrate the specified aliquots to obtain titration curves. • Determine the volume of base delivered at each time point, using the base delivery rate. • Graph the derivative of your titration curves following the instructions in the manual. • Make up a spreadsheet that will allow you to calculate the indicated values. • Perform statistical analysis on your data and complete your report form.

  10. Spreadsheet pKa Half-equivalence Point Volume Highest derivative Equivalence Point Volume

  11. Safety Concerns • Reagents: • Acetic Acid (1 N) • Sodium Hydroxide (0.1 N) / Potassium Hydroxide (0.1 N) • Eye Contact: • Irritation, tearing, redness, pain, impaired vision, severe burns and irreversible eye injury. • Skin Contact: • Severe skin irritation, soreness, redness, destruction of skin (penetrating ulcers) . May cause sensitization and / or allergic reaction. • Inhalation: • May cause coughing, serious burns, pneumonitis, pulmonary edema, and coma. • Ingestion: • Toxic. Corrosive to mucous membranes. May cause perforation of the esophagus and stomach, abdominal pain, nausea, vomiting, diarrhea, general gastro-intestinal upset.

  12. Waste • Dispose of waste in the appropriate waste receptacles. • Acidic and basic solutions / waste need to be disposed in the acid/base waste container in the fume hood. • Solutions with a pH between 6 and 8 can be disposed down the drain.

  13. Lab 5 Reminder • Read the required reading sections in your textbook and lab manual as you prepare for the next experiment. • Complete and submit the pre-lab questions. • Study for your quiz. • Submit your Lab 4 Report.

  14. After you are finished, did you… • Wash, dry and put away your glassware? • Put your buret clamp back in the drawer!? • Turn off your hotplate? • Turn off your computer (if your class is the last class for the day)? • Turn off your MicroLAB™ interface? • Turn off your monitor (if your class is the last class for the day)? • Wipe down your counter?

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