User:Khyra A. Neal/Notebook/Chem 571/2014/09/02/2014/09/02

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September 2, 2014

Stock Solution Preparations and Titrant Standardization

Preparation of Stock Solution:

0.15 M NaOH was prepared from 3.00g of NaOH and then diluted to 500 mL with H2O.

  • This molarity was chosen because NaOH is hygroscopic and the final concentration will not be able to be measured accurately.
  • Because of this property NaOH cannot be used as a primary standard.

Tirant Standardization:

Potassium Hydrogen Phthalate (KHPhth) is used a standard for NaOH.

  • Approximately 0.501 g of KHPhth was mixed with approximately 17 mL of water and titrated with NaOH stock solution. Phenolphthalein was used as an indicator and only 5 drops was added. This process was repeated two additional times and approximately the same results were yielded.
  • The final concentration of NaOH was found by averaging the results from the three trials.
  • Final NaOH concentration is 0.1485 M.

NOTE The final concentration was averaged because the results were similar for all three trials. The amount of water that was added to KHPhth is an estimate because additional water was added to the weigh boat to ensure that all KHPhth measured was used.

Trial # KHPhth (g) NaOH (mL)
1 0.501 16.70
2 0.518 17.10
3 0.519 17.10

Isoleucine Titration: Hydrophobic

Using the final concentration of 0.1485 M NaOH stock solution, the amount of isoleucine was calculated to yield 20 mL.

  • 0.3896 g of Isoleucine was dissolved in 10 mL of H2O and 10 mL of 21 mM HCl
  • The initial pH of the isoleucine solution is 3.351.
  • NaOH was titrated against the isoleucine solution in 2 mL intervals and the pH tested until the pH reached around 10. The pH was recorded every 2 mL and a titration curve was created.

NOTE The pH meter that was used was calibrated using buffers solutions of pH 4,7,and 10.