Instead of an alcoholic solution of phenolphthalein (F), a dispensed solution of blood orange juice is used as an indicator. Blood oranges contain a special plant pigment. This pigment serves as an indicator.
Erlenmeyer flask (250 ml), juicer, burette (50 ml), measuring cylinder (100 ml).
Chemicals and materials
Lemon (+red cabbage as an indicator), blood orange, sodium hydroxide solution (c = 1 mol/l)
The citrus juice is extracted and the volume of the juice is measured using a measuring cylinder (note down). You can dilute the extract with distilled water. Filtration is not necessary. The titrant is sodium hydroxide solution. Titrate to the color green.
Blood oranges are rich in organic indicators called “anthocyans”. The same experiment can also be conducted using lemons and red cabbage extract as an indicator.
Evaluation and results
For the evaluation it is sufficient to evaluate the amount of caustic soda that has to be added per 100 milliliters of juice until the indicator changes color.
The blood orange contains around 20-30% and the lemon around six times more acid (strictly speaking: titratable protons) than a sweet orange.
The solutions can be neutralized with household vinegar and poured down the drain.