Chemistry Lab Report for Vitamin C Estimation by Back(Idiometric) Titration

Vitamin c Estimation by back(idiometric) titration Mahindra (UWC of India) Chemistry lab report for back titration Name: Ashenafi Asfaw Beyene

Back (Indirect) Titration
Vitamin C estimation by Back Titration

Table1: The amount of volume (in cm3) and concentration (in M) of KI, KIO3, and H2SO4 which were used in the experiment of Vit C estimation by back titration.
VKI added to the solution/cm3 Concentration of KI added to the solution/M Volume of KIO3 added to the flasks ±0.08/cm3 Volume of H2SO4 added to the solution±0.08/ cm3 Concentration of H2SO4 added to the solution/M
15.0 0.2 10.00 5.00 1.0

Qualitative data
Colour of iodine is yellow brown
Colour of KIO3=colourless liquid
Colour remain the same after adding H2SO4 to the solution (colourless)
Colour of KIO3 and H2SO=colourless
Colour of the solution after adding 0.2MKI on KIO3 and H2SO is dark yellow brown (dark red colour appeared)
After titrating standardized 0.1M sodium thiosulphate colour of iodine changed from yellow brown to pale yellow
Colour change after adding indicator (starch) to the solution is blue (dark brown colour appears
On adding Na2S@O3 colour changes to pale yellow
Reactions: KIO3 (aq) + 5KI (aq) + 3H2SO4(aq) → 3H2O(l) + 3I2(aq) + 3K2SO4(aq) I2 (aq) + I-(aq) = I3-(aq)
2Na2S2O3 (aq) + I2(aq) → Na2S4O6(aq) + 2NaI(aq)

Table2: Burette reading for volume of Na2S2O3 (for standardization of Na2S2O3) used for the reaction of 10cm3 of 0.01 KIO3 and 5cm3 of 1,0M H2SO4 with 15cm3 of 0.2M excess KI for the formation of iodine
Initial readingcm3±0.1/cm3 Final readingcm3±0.1/cm3 Difference in readingcm3±0.2/cm3
5.9 11.4 5.5
11.4 16.7 5.3
16.7 22.0 5.3 QUALITATIVE DATA:
Average volume of burette reading=(5.5+5.3+5.3) cm3/3 = 5.37cm3
Average volume of Na2S2O3 (for standardization of

References: 1)www.educationscotland.gov.uk 2)http://www.scribd.com/doc/8303174/59-Titration-Calculations 3) ï Harris chapter 16, especially section 16-7.