Question

Vitamin C tablets contain ascorbic acid (C6H8O6= 176.1232 g/mol) and a starch "filler" which holds them together. Your goal today is to determine how much vitamin C or ascorbic acid, HC6H7O6 is present in the tablet. This can be determined by titrating ascorbic acid, HC6H7O6 with calcium hydroxide solution, Ca(OH)2(aq) (74.0918 g/mol) according to the following equation: 2HC6H7O6(aq) + Ca(OH)2(aq) ---> Ca(C6H7O6)2(aq) + 2H2O(l)

First you must make 500 mL of a 0.1012 M standard solution of Ca(OH)2 from a 10.45% mass solution of Ca(OH)2 (density 1.0634 g/mL). How many mL of the 10.45% mass solution of Ca(OH)2 would you use to prepared this solution? Describe how to prepare this solution.

1 tablet (0.5702g) of vitamin C/ascorbic acid and filler is dissolved in 100.00mL of water and placed in an Erlenmeyer flask. The ascorbic acid is titrated with the 0.102 M Ca(OH)2 solution. The intital reading on the buret was 10.35 mL and final reading on the buret was 28.15 mL. Determine the number of moles oc Ca(OH)2 added to the solution.

Answer 1

a) molarity of ca(OH)2 solution available = (m/m)%*d*10/M

           = 10.45*1.0634*10/74.0918

           = 1.5 M

from dilution formula

   M1V1 = M2V2

(1.5*V1) = (0.1012*500)

V1 = Vol of 10.45% ca(OH)2 required = 33.73 ml

take 33.73 ml of 10.45%mass Ca(OH)2 solution and add water up to 500 ml solution.

b)
    volume of Ca(OH)2 added = 28.15-10.35 = 17.8 ml

   No of mol of Ca(OH)2 added = v*M = 17.8*0.1012

               = 1.8 mmol

               = 1.8*10^-3 mol