Colorimetric Pipetting Exercise

Submitted by kdorfman on Wed, 06/21/2023 - 18:16

Mix 200 mM mono- (acid) and di-basic sodium phosphate (base) with bromothymol blue to get a range of colors from yellow to blue.

Put a 5 uL drop of bromothymol blue in each square, then add the given amounts of sodium phosphate

pH 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8
Na2HPO4 2.5 3.7 5.3 7.5 9.8 12.2 14.4 16.2 17.4 18.3
NaH2PO4 17.5 16.3 14.7 12.5 10.2 7.8 5.6 3.8 2.6 1.7

Per exercise, need:

  • 107.3 uL Na2HPO4
  • 92.7 uL NaH2PO4
  • 50 uL bromothymol blue (0.04% aqueous) (e.g., Fisher LC120501, $25 for 500 mL))
  • printed buffer table (see linked file)
  • parafilm

So aliquot

reagent actual vol aliquot
Na2HPO4 107.3 250
NaH2PO4 92.7 250
bromothymol blue 50 125
pipet buffer table