User:Alicia Rasines Mazo/Notebook/CHEM-571 Experimental Biological Chemistry/2014/09/02

From OpenWetWare
Jump to: navigation, search
Owwnotebook icon.png Project name Report.pngMain project page
Resultset previous.pngPrevious entry      Next entryResultset next.png

Task for September 2 2014

  • Prepare Stock Solutions
  • Standardize titrant
  • Titrate Amino Acids

For full method refer to Dr. Douglas' notebook

Preparation of Stock Solutions

  • A stock solution of NaOH was prepared using 3.0953 g of the hydroscopic material. Distilled water was added to make up a 500 mL solution.
  • 200 μM stock solutions were made for isoleucine, aspartic acid, histidine, tyrosine and alanine. 100 mL solutions were prepared.
    • 20 μmol × 131.17 g/mol = 0.00262 g of isoleucine
    • 20 μmol × 133.10 g/mol = 0.00266 g of aspartic acid
    • 20 μmol × 155.16 g/mol = 0.00310 g of histidine
    • 20 μmol × 181.19 g/mol = 0.00362 g of tyrosine
    • 20 μmol × 89.09 g/mol = 0.00178 g of alanine

Standardization of NaOH solution

  • NaOH is a very hydroscopic material and quickly absorbs water from the environment, which makes it a secondary standard solution. Potassium hydrogen phthalate (KHP) was used to titrate NaOH.
  • 5 drops of phenolphthalein were added
Standardization of NaOH solution
Trial 1 Trial 2 Trial 3
Initial Volume (mL) 0.1 0.1 0.7
Final Volume (mL) 16.7 17.2 17.8
Volume titrated (mL) 16.6 17.1 17.1
Mass of KHP (g) 0.501 0.518 0.519
Moles of KHP 0.002453 0.002536 0.002541
  • Average moles of KHP titrated by NaOH = 0.002538
  • Considering concordant results (and given that the first trial was the rough estimate), it took 17.1 mL of NaOH to titrate 0.002538 moles of KHP
  • Concentration of NaOH = 0.1485 M

Amino Acid Titrations

It was suggested that amino acid solutions be made that would require 20 mL of NaOH to be titrated. <br.> Given that 0.1485 M NaOH was used, 0.00297 moles of each amino acid were required.

  • 0.00297 mol × 131.17 g/mol = 0.3895 g isoleucine
  • 0.00297 mol × 155.10 g/mol = 0.4608 g histidine

10 mL of 21 mM HCl were added, in addition to 10 mL water. <br.> The titration curves were as follows: <br.> Isoleucine titration 020914.png <br.> Histidine titration 020914.png