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

From OpenWetWare

Jump to: navigation, search
Project name Main project page
Previous entry      Next entry

Contents

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 0.10.7
Final Volume (mL) 16.7 17.2 17.8
Volume titrated (mL) 16.6 17.117.1
Mass of KHP (g) 0.501 0.5180.519
Moles of KHP 0.002453 0.0025360.002541
  • 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.
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.
The titration curves were as follows:
Image:Isoleucine titration 020914.png
Image:Histidine titration 020914.png


Personal tools