Beets change from red to
purplish in very basic solution.
Blackberries, black currants, and black raspberries
change from red in acids to dark blue or violet in basic solution.
Blue and red grapes contain
several different pH-sensitive anthocyanins. For example, blue grapes are
colored by a monoglucoside of malvinidin that changes from deep red in acidic
solutions to violet in basic solution.
Red wines naturally contain
these same pigments.
Blueberries change from blue
(around pH 2.8-3.2) to red in a strongly acidic solution.
Cherries and cherry juice is
bright red in acidic solution but purple to blue in basic solution.
Curry powder and tumeric are
spices that contain a bright yellow pigment called curcumin (which is not
an anthocyanin). It turns from yellow at pH 7.4 to red at pH 8.6.
Delphinium petals contain an
anthocyanin called delphinin, which changes from bluish red in acid to blue to
violet in basic solution.
Geranium petals contain
pelargonin, an anthocyanin which changes from orange-red in acid solution to
bluish in basic solution.
Horsechestnut leaves can be
ground with alcohol to extract esculin, a fluorescent dye. Esculin changes from
colorless at pH 1.5 to fluorescent blue at pH 2. Shine a black (ultraviolet)
light on the indicator to get the full effect.
Morning glories contain an
anthocyanin called "heavenly blue anthocyanin" which changes from
purplish red at pH 6.6 to blue at pH 7.7.
Onion is an olfactory
indicator. The onion odor isn't detectable in strongly basic solutions. Red
onion can act as a visual indicator at the same time. It changes from pale red
in acid solution to green in basic solution.
Petunia petals contain
petunin, an anthocyanin that changes from reddish purple in acid to violet in
basic solution.
Purple peonies contain
peonin, which changes from reddish purple or magenta in acid solution to deep
purple in basic solution.
Red cabbage contains a
mixture of anthocyanins and other pigments that indicate a wide range of pH. The
photograph at right shows how red cabbage juice changes from deep red at pH 1 to
purple at pH 7 to to green at pH 12. At higher pH (13-14) it turns yellow.
Rose petals contain the
oxonium salt of cyanin, and they turn blue in basic solution. (The potassium or
calcium salt of the same pigment makes cornflowers blue!)
Vanilla extract,
like onion, is an olfactory indicator. The vanilla odor isn't detectable in
strongly basic solution because vanillin exists in ionic form at high pH.
