Biological background

Anthocyans are a group of dyes occuring in colours from red to blue. They are water-soluble and therefore found in the vacuole of a plant-cell.
Their colour can be changed by shifting the pH-value.
In plants usually a mixture of various anthocyans are present. Some of these extracts can be used as indicators.


Experiments with Red Wine

Take 3 test-tubes and fill each one to 1/4 with Red wine.
At the teacher´s table 3 beakers with 3 clear liquids are given: Nr.1 contains an acid,
Nr. 2 a base and Nr. 3 an unknown liquid.
Add to t.t. 1 three pipettes of the liquid Nr.1 and do the same with t.t.2 / liquid 2 or
t.t. 3 / liquid 3
Finally add to t.t. 1 another 6 pipettes of the base

Observations ? – Conclusions ?


Extract from Red Cabbage

Cut a red cabbage into pieces and cover them for at least one hour (evtl. one day) with spirit. Filter into a plastic bottle and store in the fridge. The extract can be used for plenty of months.


Experiments with Red Cabbage Extract

1) Quality as indicator

Required: Solutions of various definite pH-value

Fill each test-tube to 1/4 with one given solution of definite pH.
Add the same amount of the red cabbage extract.
Draw a table pH-value / colour of extract


2) Production of indicator paper

Soak a filter paper with the rc-extract and allow to dry.
Cut the paper into small sheets.
Check with these paper sheets the pH-value of various household items.


3) The Red Cabbage Artist

Soak drawing paper with red cabbage extract and allow to dry.
Check in a drug store for household items of various pH-value equipped with a spraying head. - Be a spray artist!