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.
Benefits
- Modern spectrophotometer with display
- Spectrophotometer can be used for many other applications
- Detailed operating instructions
Tasks
- 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.
- 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
Necessary accessories
- Precision balance 620 g / 0,001 g
Scope of Supply
| Device Name | Item no. | Qty |
|---|
| Cell for spectrophotometer, optical glass | 35664-00 | 2,00 |
| Ethyl alcohol, absolute 500 | 30008-50 | 1,00 |
| Thermometer -10...+50 °C | 38034-00 | 1,00 |
| Volumetric pipette, 1 ml | 36575-00 | 1,00 |
| Microspoon, steel | 33393-00 | 1,00 |
| Hydrochloric acid,0.1M 1000 | 48452-70 | 1,00 |
| Pasteur pipettes, 250 pcs | 36590-00 | 1,00 |
| Beaker, DURAN®, tall form, 150 ml | 36003-00 | 3,00 |
| Buffer solution, pH 9 1000 | 30289-70 | 1,00 |
| Rubber caps, 10 pcs | 39275-03 | 1,00 |
| Volumetric pipette, 5 ml | 36577-00 | 1,00 |
| Wash bottle, plastic, 500 ml | 33931-00 | 1,00 |
| Shimadzu UV-1280 Spectrophotometer 190-1100 nm | 35655-99 | 1,00 |
| Pipettor | 36592-00 | 1,00 |
| Volumetric flask, Borosilicate, 50 ml, IGJ12/21 | 36547-00 | 3,00 |
| Weighing dishes, square shape, 84 x 84 x 24 mm, 25 pcs. | 45019-25 | 1,00 |
| Volumetric pipette, 10 ml | 36578-00 | 1,00 |
| Funnel, glass, top dia. 50 mm | 34457-00 | 1,00 |
| Graduated cylinder, Borosilicate, 250 ml | 36630-00 | 1,00 |
| Volumetric flask 1000ml, IGJ24/29 | 36552-00 | 3,00 |
| Thymol blue indicator | 31896-02 | 1,00 |
| Caustic soda sol.,0.1M 1000 | 48328-70 | 1,00 |
| Pipette dish | 36589-00 | 1,00 |
| Water, distilled 5 l | 31246-81 | 1,00 |
Downloads and Documents