On the other hand, a higher pH denotes a stronger base. Thus a base with pH 8 is considered a weak base, whereas a base with pH above 12 is considered a strong base. Red cabbage contains a chemical called anthocyanin, which changes color when hydrogen ions are added or removed from it. In an acid, red cabbage turns red. In a base, red cabbage juice turns blue, green or yellow, depending of the strength and nature of the base.
Club soda is an interesting one to try.
Observe the color when red cabbage juice is added to club soda from a freshly opened can or bottle. Observe the color change. Initially, the club soda is slightly acidic because of the large amount of carbon dioxide dissolve in it. Boiling the club soda drives off the carbon dioxide and leaves the solution slightly basic because of the other chemicals remaining in it. Note the point when the color of the solution changes to purple and then to a color characteristic of a base.