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
Sample #
|
Original KHP Amount Dried (g)
|
1 |
6.8079
|
2 |
6.8075
|
3 |
6.8076
|
Titration Procedures and Preparations
- In a clean burette, pour in the 0.2M NaHCO3 solution until it reaches the top
- Turn the stopcock at the bottom of the burette to allow the solution to pass through the tip
- In a clean beaker, run the solution from the burrette until 0.2M NaHCO3 solution volume reaches the 0.00mL calibration mark
- Record the initial starting point and then turn on the stir plate beneath the burette
- Next, place one of the acetylation PVOH solutions onto the stir plate
- While stirring the PVOH solution, add ~2 drops of bromothymol blue indicator
- Begin titrating by turning the stopcock on the burette allowing the 0.2M NaHCO3 solution to steadily stream out
- Slow the pace of the 0.2M NaHCO3 solution to drops when the PVOH solution begins to turn red in color
- Once the solution completely to turns red, stop titrating by turning the stopcock to OFF position
- Record the new 0.2M NaHCO3 volume within the burette
REPEAT THE ABOVE STEPS AGAIN FOR THE NEXT THREE PVOH SOLUTIONS
Titration Trial #
|
PVOH Solution (g)
|
Acetic Acid (mL)
|
Bromothymol Blue Indicator (drops)
|
Initial Burette Volume(mL)
|
Final Burette Volume(mL)
|
Sodium Bicarbonate Used (mL)
|
1 |
1.0043 |
0.26 |
2 |
0.5 |
42.5 |
42
|
2 |
1.0052 |
0.52 |
2 |
0.0 |
43.2 |
43.2
|
3 |
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.
- For titration, each PVOH solution after the indicator was added blue; however, when titration with the 0.2M NaHCO3 solution, at equilibrium each solution turned red.
- After several hours and days, it was decided that the KHP solution necessary for standardization would not form a homogeneous mixture -- KHP precipate falling out of solution -- therefore, only solid samples would be used. The KHP was not placed into solution for standardization.
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