Answer:
[tex]\frac{[magenta\ phenolphthalein]}{[colorless\ phenolphthalein]}=31.62[/tex]
Explanation:
Considering the Henderson- Hasselbalch equation for the calculation of the pH of the buffer solution as:
[tex]pH=pKa+\log\frac{[base]}{[acid]}[/tex]
Where Ka is the dissociation constant of the acid.
pKa of phenolphthalein = 9.40
pH = 10.9
So,
[tex]10.9=9.40+\log\frac{[magenta\ phenolphthalein]}{[colorless\ phenolphthalein]}[/tex]
[tex]\frac{[magenta\ phenolphthalein]}{[colorless\ phenolphthalein]}=31.62[/tex]
