User:Douglas M. Fox/Notebook/AU CHEM-571 F2011 Lab Support/2017/09/06

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Titrant Standardization

NaOH is hydroscopic and cannot be measured accurately enough to use as a primary standard. The primary standard most often used for NaOH is potassium hydrogen phthalate (KHPhth). Standardization is performed by simple titration

  • Obtain a clean buret
  • Rinse the buret with about 10 mL of your NaOH solution. Be sure to drain some through the tip. You may use a funnel to fill.
  • Empty completely and repeat 1 - 2 times.
  • Fill completely with NaOH and drain some through the tip. Tap to remove all air bubbles. Remove the funnel.
  • Record the initial volume. It does not have to equal one, but you need at least 25 mL of titrant. Remember, top line reads 0 mL.
  • Transfer about 0.001 g of KHPhth to an Erlenmeyer flask and add 15 - 30 mL of water. (How did I get these values?)
  • Or, transfer 20 mL of 0.2 mM KHPhth that you have prepared (or 1 mL of 4 mM if you needed higher mass for accuracy)
  • Add a few drops of phenolphthalein solution
  • Titrate until the solution turns pink. If it is dark red, you overshot. You can periodically rinse sides with wash bottle.
  • Repeat at least twice

Amino Acid Titration

  • Transfer 10 mL of your 250 μM amino acid solution to a clean and dry 100 mL beaker (Why does it need to be dry?)
  • Add 10 mL of 200 μM HCl and 10 mL water
  • Insert your pH probe and record the initial value
  • Add titrant in 2 - 4 mL intervals. Swirl gently, being careful not to splash. Record the pH.
  • Continue until the pH reaches at least 10 or 11.
  • For the first trial, you will likely skip past the inflection points. On 2nd & 3rd trials, slow addition to 0.2 or 0.1 mL near inflections.
  • Repeat for all 3 amino acids