User:Elizabeth Ghias/Notebook/Experimental Chemistry/2013/02/01
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To calculate the number of OH groups in polyvinyl alcohol (MW = 146000 - 186000) and to prepare PVOH films
OH Group Calculations
PVOH repeating unit structure = CH2-CH-OH → MW = 12·2+4+16 = 44
MW min: 146,000/44 = 3318.13 PVOH units per molecule → 3318.13 OH groups per molecule
MW max: 186,000/44 = 4227.27 units per molecule → 4227.27 OH groups per molecule
MW avg: 166,000/44 = 3772.73 units per molecule → 3772.73 OH groups per molecule
0.5g PVOH / 166,000 g/mol = 3.012E-6 moles PVOH
3.012E-6 moles PVOH × 3773.73 OH groups per molecule = 0.0114 OH groups in 0.5 g PVOH
0.0114 OH groups in 0.5 g PVOH · 6.022 x 1023 molecules/mol = 6.86508 x 1021 OH groups in 0.5 g PVOH
Next, we tested the concentrations of isopropanol that can bind to the OH groups in 0.5 g PVOH. We decided to start with 10% OH groups bound to isopropanol and decrease the concentration from there.
[6.86508 x 1021 OH groups x 1 molecule isopropanol/1 molecule OH] / 6.022 x 1023 molecules/mol = 0.00114 moles isopropanol
0.00114 moles isopropanol x 60.1 g/mol = 0.068514 g isopropanol
0.068514 g isopropanol / 0.786 g/mL = 0.0872 mL isopropanol
Isopropanol solutions were then prepared by taking 10 mL of isopropanol (see notes) and putting it in a tube. Serial dilutions with water were then carried out to create 10%, 1% and 0.1% solutions. To create these solutions, 1 mL of solution was added to 9 mL of water. 0.872 mL of each solution was added to its respective film.
All films were heated on a hot plate until the PVOH dissolved in the water. For films 5,6, and 7, additional water was added to the gel to assist in the dissolution. Once dissolved, the film was removed from heat and any additional reagents were added while the gel was stirred. When isopropyl and glutaraldehyde were added, the isopropyl would be added first and then would stir for roughly 2 to 3 minutes. Glutaraldehyde was added last. Once prepared, the films were poured into a large plastic dish and were allowed to evaporate over the weekend.