A series of titrations of lactic acid, CH₃CH(OH)COOH (pK_a = 3.86) is planned. About 1.00 mmol of the acid will be titrated with NaOH(aq) to a final volume of about 100 mL at the equivalence point. 

(a) Which acid–base indicator from Figure 17-7 would you select for the titration? To assist in locating the equivalence point in the titration, a buffer solution is to be prepared having the same pH as that at the equivalence point. A few drops of the indicator in this buffer will produce the color to be matched in the titrations. 

(b) Which of the following combinations would be suitable for the buffer solutions: CH₃COOH–CH₃COO^-, H₂PO₄^-–HPO₄^2-or NH₄⁺–NH₃? 

(c) What ratio of conjugate base to acid is required in the buffer?

Figure 17-7

Transcribed Image Text:

Indicator Alizarin yellow-R Thymolphthalein Phenolphthalein Thymol blue (base range) Phenol red pH- Bromthymol blue Chlorphenol red Methyl red Bromcresol green Methyl orange Bromphenol blue Thymol blue (acid range) Methyl violet 1 0 Yellow Red (b) 2 8 3 Violet Yellow Red Yellow Yellow 4 Red Git 5 (a) 10 Yellow 6 Yellow Yellow Blue 7 Yellow-orange Blue-violet Yellow Colorless Yellow 1 8 Red Blue 0 Red I 9 Colorless 10 Yellow Red Blue 11 Blue 12 Violet