Characterizations of pH Route and Absorption Spectrum of Purple Cabbage Extract (Brassicao Oleracea L.) as a Natural Indicator of the Acid-Base Titration

Purple cabbages can produce color. It has been known that the pigment in plants, in general, is an anthocyanin compound that changes the color at every pH change so that purple cabbages have potential as a natural indicator of the acid-base titration. This study aims at determining the route of pH, the absorption spectrum for any changes in pH, the precision and accuracy of the use of fresh purple cabbage extract as a natural indicator of the acid-base titration. The research was begun with the manufacture of the purple cabbage indicator by extracting fresh and dry purple cabbages by using hot water. The determination of pH route was done by dripping the purple cabbage indicator into each buffer solution. Observations on color changes were conducted visually. Furthermore, absorbance measurements were taken for each buffer solution that has been poured with purple cabbage indicator for estimating the maximum price of the wavelength. Tests of the precision and accuracy of the purple cabbage indicator were done by applying the acid-base titration. Titration tests were performed 5 times to determine the deviation degree and the percent recovery. The results showed that the pH route of the fresh purple cabbage extract was 10. 7 to 11.2 while the pH routes of the dry purple cabbage extract were 6.2 to 7.0 and from 10.0 to 10.7. The absorption spectrum of the fresh and dry purple cabbage extract showed almost similar characters. The most intense color for the fresh purple cabbage extract was shown at pH 10.2 while in the dry purple cabbage extract, it was at pH 10.7 and no shift of maximum wavelength (380 nm) at each change of pH. The use of the fresh purple cabbage extract was careful and accurate when used in the strong acid- strong base titration and the weak acid-weak base titration. Keywords : natural indicator, pH route, absorption spectru