b) Calculate the purity in vitamin C of the table (in percent). 1. The amount of

Question

b) Calculate the purity in vitamin C of the table (in percent). 1. The amount of ascorbic acid in tablets (vitamin C, molar mass = 176.12 g) is determined by reaction with bromine, followed by the titration of hydrobromic acid with a standard base. The necessary equations are (balanced): C6H8O6 + Br2 right arrow C6H6O6 + 2 HBr HBr + NaOH right arrow NaBr + H2O For this analysis, a 500. mg tablet of vitamin C is dissolved in water and reacted with excess bromine. The resulting solution was titrated with 43.20 mL of 0.125 M NaOH. a) Calculate the quantity of hydrobromic acid (HBr) produced, in moles.

Explanation / Answer

a) 43.20 mL of 0.125 M NaOH is consumed.

Number of moles of NaOH = Molarity x Volume (in L) = 5.4 x 10-3 mol

The chemical reaction, NaOH + HBr ---------> NaBr + H2O indicates that NaOH and HBr react in eqimolar ratio.

So, 5.4 x 10-3 moles of NaOH react with 5.4 x 10-3 of HBr.

So, the number of moles of HBr =5.4 x 10-3 mol

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The amount of HBr in moles = 5.4 x 10-3 mol.

From the chemical reaction, C6H8O6 + Br2 -------> C6H6O6 + 2HBr

So, 2 moles of HBr are produced from 1 mole of Vit. C

5.4 x 10-3 mol of HBr are produced by 5.4 x 10-3 / 2 = 2.7 x 10^-3 mol of Vit. C (Practical value)

500 mg of Vit. C is taken.

So, moles of vit. C = 0.5 g / 176.12 = 2.84 x 10-3 mol (Theoretical value)

Purity = Practical / Theoretical x 100 = (2.7 x 10^-3 mol x 2.84 x 10-3 mol) x 100

= 95.10%

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