Dissociation constants

Product No: P3031101

Principle

The coloured indicator thymol blue is a weak acid that is partially dissociated in aqueous solution, whereby  non-ionized and ionized forms show absorption maximums at different wavelengths in the visible range. Photometric measurements in the visible spectral range can therefore be used to advantage to determine the position of the Ka and pKa values of the indicator which characterize dissociation equilibrium.

Tasks

  1. Experimentally determine the extinction (absorbance) of an aqueous solution of thymol blue (thymolsulphonephthalein) in dilute HCl, NaOH and a buffer of known pH value as a function of wavelength between 400 and 700 nm at constant concentration and constant temperature.
  2. Calculate the dissociation constant (indicator constant) Ka from the measurement results.

What you can learn about

  • True and potential electrolytes
  • Strong and weak acids
  • Law of mass action
  • Dissociation constants and pKa values
  • Henderson-Hasselbalch- Equation
  • UV-vis spectrometry
  • Lambert-Beer's Law
  • Photometry
Materiallist (Excerpt) Product Amount
Spectrophotometer 190-1100 nm 35655-93 1
Precision Balance, Sartorius QUINTIX513-1S, 510 g / 0,001 g 49282-99 1
Cells for spectrophotometer, optical glass, 2 pcs. 35664-02 1
Ethyl alcohol, absolute 500 ml 30008-50 1
Buffer solution, pH 9 1000 ml 30289-70 1
Thermometer -10...+50 °C 38034-00 1
Thymol blue indicator 5 g 31896-02 1
Caustic soda sol.,0.1M 1000 ml 48328-70 1
Volumetric flask 1000ml, IGJ24/29 36552-00 3
Pipette dish 36589-00 1
Hydrochloric acid,0.1M 1000 ml 48452-70 1
Pipettor 36592-00 1
Water, distilled 5 l 31246-81 1
Graduated cylinder 250 ml 36630-00 1
Pasteur pipettes, 250 pcs 36590-00 1
Weighing dishes, square shape, 84 x 84 x 24 mm, 25 pcs. 45019-25 1
Volumetric flask 50 ml, IGJ12/21 36547-00 3
Glass beaker DURANŽ,tall, 150 ml 36003-00 3
Rubber caps, 10 pcs 39275-03 1
Volumetric pipette, 10 ml 36578-00 1
Microspoon, steel 33393-00 1
Volumetric pipette, 5 ml 36577-00 1
Funnel, glass, top dia. 55 mm 34457-00 1
Volumetric pipette, 1 ml 36575-00 1
Wash bottle, plastic, 500 ml 33931-00 1

Title Product Language
TESS expert Handbook Laboratory Experiments Chemistry 16504-12 ENG


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