Adapted from Funscience
We start with red cabbage: Boiled for half an hour in water. Recovering the extract formed: This is the color indicator.
With a drop of vinegar (solution of $CH_3COOH$) is observed a turn at red. This turn is characteristic of acids. So $CH_3COOH$ (ethanoic acid) is also called acetic acid (acetum = vinegar)
A light bulb is used to study the conductivity of solutions. The result in the case of acetic acid: ..and in the case of chlorhydric acid (completely dissociated):
The dissociation of acetic acid is incomplete or weak:
$CH_3COOH$ $+$ $H_2O$ $\rightleftarrows $ $CH_3COO^-$ $+$ $H_3O^+$ In a simplified form: $CH_3COOH$ $ \rightleftarrows $ $ CH_3COO^-$ $+$ $H^+$