Question

The pigment cyanidin aglycone is one of the anthocyanin molecules that gives red cabbage (Brassica oleracea var. capitata f. rubra) its characteristic red coloration. Many young chemists have used this “red cabbage indicator” to study acid–base chemistry. Estimate the pH range at which cyanidin aglycone shows a color change. Anth-H Anth- + H+ Ka = 1.3 x10 -7

Answer 1

Hey there!

The pH range of a buffer is the pH window where in the uffer resists the changes in pH of the solution upon addition of small amounts of acid or base. Generally, the pH range of a buffer solution is equal to pKa ±1.

for this system :

ka= 1.3*10⁻⁷ , hence

pKa= - log (Ka)

pKa =  - log ( 1.3*10⁻⁷)

pKa = 6.88

Therefore, hence the buffer can be used in pH range of 5.88 to 7.88.

Hope that helps!