“Enchanting fluorescein” experiment
Why fluorescein radiates light under UV
This colorful experiment demonstrates the ability of some substances to radiate light under the impact of an external energy source (usually an ultraviolet one). From this experiment, you will find out why fluorescent (ultraviolet) paints glow which are used in banknotes, and decorating rooms and night clubs. Fluorescein is also used to turn rivers green on St. Patrick’s Day.
Care must be taken when working with an alkali and its solutions.
Reagents and equipment:
- fluorescein 2 g;
- sodium hydroxide 2 g;
- distilled water;
- beaker 5 l.
We prepare the alkaline solution: we sprinkle 2 g of NaOH into the beaker, and add 50 ml of distilled water and stir. Then we add 2 g of fluorescein to the solution. We get a saturated solution of fluorescein salt. We pour water into the beaker, turn off the light and turn on the UV lamp. With a pipette we drip the solution of fluorescein salt into the water. Enchanting green rings and “clouds” form.
Fluorescence is the radiation of light by a substance, the atoms of which have received an abundant amount of energy (for example under the impact of ultraviolet light). Without an energy source, fluorescence stops. Many substances have this property, for example: fluorescein, quinine, the chlorophyll of plants and many others When fluorescein is dissolved in an alkaline solution of NaOH, a water-soluble salt forms. Depending on the lighting and concentration of the solution, the fluorescein changes color. When several drops of a saturated solution of fluorescein are added to water, it glows green in ultraviolet light.