User:Karlena L. Brown/Notebook/PVOH Research/2012/11/09

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OBJECTIVES

  • Prepare PVOH films for Acetylation Reactions
  • Titrate PVOH film solutions

General Formula for reactions

Polyvinyl alcohol + [HoAc]→Polyvinyl acetate

Acetylation Reaction Protocol & Film Preparation

  • In 10mL beaker, weigh out ~ 1.0 grams PVOH (MW 22K)
  • Then, using a graduated cylinder add ~ 3-4 mL H2O to the beaker
  • After adding and combining PVOH (MW 22K) in a small beaker with H2O, add a stir bar and prepare to stir solution
  • On hot plate, stir and heat beaker solutions at 70-80°C for ~ 12 min or until PVOH dissolves
  • Once PVOH solids thoroughly dissolve in solution, add a small portion of acetic acid (HoAc)
  • In addition, add ~2 drops of HCl to the solution and continue to stir for an hour
  • Allow the solution to cool and prepare for titration

REPEAT PROCEDURE ABOVE FOUR TIMES TO PREPARE FOUR FILMS

PVOH Mass (g) Acetic Acid (mL) Hydrochloric Acid (drops) Total Volume(mL) Total Volume(mL)
1.0062 1.30 2 3.70 7
1.0043 0.26 2 4.74 7
1.0052 0.52 2 4.48 7
1.0027 0.78 2 4.22 7

Acetylation Reaction Calculations

1:1 HoAc Reaction Ratio: 

  MW R-CH2CHOH-R: 44.00 g/mol
  MW Acetic Acid (HoAc): 60.00 g/mol
  1.0g PVOH × (1 mol PVOH/44.00g PVOH) × (1 mol HoAc/1 mol PVOH) × (60.00g HoAc/1 mol HoAc) = 1.36g HoAc
  1.36g HoAc × (1mL HoAc/1.05g HoAc)= 1.30mL HoAc

20% HoAc Reaction Ratio: 

  MW R-CH2CHOH-R: 44.00 g/mol
  MW Acetic Acid (HoAc): 60.00 g/mol
  1.0g PVOH × (1 mol PVOH/44.00g PVOH) × (0.2 mol HoAc/1 mol PVOH) × (60.00g HoAc/1 mol HoAc) = 0.27g HoAc
  0.27g HoAc × (1mL HoAc/1.05g HoAc)= 0.26mL HoAc

40% HoAc Reaction Ratio: 

  MW R-CH2CHOH-R: 44.00 g/mol
  MW Acetic Acid (HoAc): 60.00 g/mol
  1.0g PVOH × (1 mol PVOH/44.00g PVOH) × (0.4 mol HoAc/1 mol PVOH) × (60.00g HoAc/1 mol HoAc) = 0.55g HoAc
  0.55g HoAc × (1mL HoAc/1.05g HoAc)= 0.52mL HoAc

60% HoAc Reaction Ratio: 

  MW R-CH2CHOH-R: 44.00 g/mol
  MW Acetic Acid (HoAc): 60.00 g/mol
  1.0g PVOH × (1 mol PVOH/44.00g PVOH) × (0.6 mol HoAc/1 mol PVOH) × (60.00g HoAc/1 mol HoAc) = 0.82g HoAc
  0.82g HoAc × (1mL HoAc/1.05g HoAc)= 0.78mL HoAc

Titration Solution Preparation

0.2M Sodium Bicarbonate (NaHCO3)solution for titration preparation:

  • Weigh out ~16.802g NaHCO3
    (Actual NaHCO3 Mass= 16.8046g)
  • Add the NaHCO3 solids to a 250mL closed cap plastic bottle
  • Next, add ~2500mL of H2O to the bottle along with large magnetic stir bar
  • Place container on a stir plate and stir solution for ~10 minutes until all solids dissipate
  MW NaHCO3: 84.01 g/mol
  0.2M NaHCO3 × 1L H2O × (84.01g NaHCO3/1 mol NaHCO3)= 16.802g NaHCO3


1M Potassium Hydrogen Phthalate (KHP) solution for titration preparation:

  • Weigh out ~ 20g KHP and place the solids in a metal pan
    (Actual KHP Mass= 20.424g)
  • Place the metal pan with the solids in an oven at 120°C for 1 hour to dry
  • Once dried, add the KHP solids to a 100mL volumetric flask
  • Next, add a large magnetic stir bar to the flask and fill with distilled H2O to the calibrated line
  • Allow the mixture to stir for 72 hours
 MW NaHCO3: 204.24 g/mol
 1M KHP × 0.1L H2O × (204.24g KHP/1 mol KHP)= 20.424g KHP

Titration Procedures and Preparations

  1. In a clean burette, pour in the 0.2M NaHCO3 solution until it reaches the top
  2. Turn the stopcock at the bottom of the burette to allow the solution to pass through the tip
  3. Run the solution through the burrette until the 0.2M NaHCO3 solution volume reaches the 0.00mL calibration mark
  4. Record the initial starting point and then turn on the stir plate beneath the burette
  5. Next, place one of the acetylation PVOH solutions onto the stir plate
  6. While stirring the PVOH solution, add ~2 drops of bromothymol blue indicator
  7. Begin titrating by turning the stopcock on the burette allowing the 0.2M NaHCO3 solution to steadily stream out
  8. Slow the pace of the 0.2M NaHCO3 to drops when the PVOH solution begins to turn red in color
  9. Once the solution completely to turns red, stop titrating by turning the stopcock to off position
  10. Record the new 0.2M NaHCO3 volume within the burette

REPEAT THE ABOVE STEPS AGAIN FOR THE NEXT THREE PVOH SOLUTIONS

PVOH Solution (g) Acetic Acid (mL) Bromothymol Blue Indicator (drops) Initial Burette Volume(mL) Final Burette Volume(mL) Sodium Bicarbonate Used (mL)
1.0043 0.26 2 0.5 42.5 42
1.0052 0.52 2 0.0 43.2 43.2
1.0027 0.78 2 0.1 42.8 42.7

Notes

  • Only the repeating unit of PVOH (22K) was focused upon when calculating % weight of HoAc additions to each solution (titration preparation)
  • Molecular weight of repeating polyvinyl alcohol unit [C2H3OH] = 44.06g/mol
  1g PVOH(1 mol PVOH unit/44.06g PVOH) x (1 mol OH/1 mol PVOH)= 0.022696 mol PVOH
  • In addition, the 1:1 HoAc ratio solution overheated by boiling; therefore, this solution was not used for the titration analysis.
  • Also the actual amount of NaHCO3 used was 16.8046g; it is not necessary to prepare solution in a volumetric flask because the solution will be standardize to find the actual concentration.


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