Sketch the titration curve from Problem 123 by calculating the pH at the beginning of the titration, at one-half of the equivalence point, at the equivalence point, and at 5.0 mL beyond the equivalence point. Pick a suitable indicator for this titration from Table 18.1.

Problem 123

A 0.552-g sample of ascorbic acid (vitamin C) was dissolved in water to a total volume of 20.0 mL and titrated with 0.1103 M KOH. The equivalence point occurred at 28.42 mL. The pH of the solution at 10.0 mL of added base was 3.72. From this data, determine the molar mass and K_a for vitamin C.

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TABLE 18.1 Ranges of Color Changes for Several Acid-Base Indicators pH 4 5 6 7 0 Crystal Violet Thymol Blue Erythrosin B 2,4-Dinitrophenol Bromphenol Blue Bromocresol Green Methyl Red Eriochrome* Black T Bromocresol Purple Alizarin Bromthymol Blue Phenol Red m-Nitrophenol o-Cresolphthalein Phenolphthalein Thymolphthalein Alizarin Yellow R 1 *Trademark of CIBA GEIGY CORP. 2 3 wwwww 8 9 10 11 12