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Lab Report: Try things out 3
Evaluation of commercial vitamin C tablets
Name: Cheung Chun Hin, Harry Class: 6L (12) Date: 14-10-2009
To determine the content material of vitamin C in commercial tablets (redox titration and back again titration)
Principle of method:
Nutritional C, which is ascorbic acidity, reacts with iodine swiftly in an acid medium.
C6H8O6 (aq) + I2 (aq) C6H6O6 (aq) & 2H+(aq) + 2I- (aq)
Since iodine dissolves a bit in drinking water, ascorbic acid cannot be titrated directly with a standard remedy of iodine. Therefore , back again titration technique is employed in this experiment. Within an acidic moderate, potassium iodate(V) reacts with potassium iodide to produce iodine in situ.
KIO3 (aq) + 5KI (aq) + 3H2SO4 (aq) 3I2 (aq) + 3H2O (l) + 3K2SO4 (aq)
The iodine produced reacts with ascorbic acid immediately. Then, the iodine remaining is titrated by a normal solution of sodium thiosulphate.
2Na2S2O3 (aq) + I2 (aq) Na2S4O6 (aq) + 2NaI (aq)
Because the concentration of standard salt thiosulphate option is unknown, sodium thiosulphate solution is first titrated against iodine.
Since the end-point of the titration is certainly not observable, starch solution is definitely added to behave as an indication since a complex of iodine and starch will form and lead to a dark blue shade. This creation of sophisticated is invertable so that the moment all the iodine is reacted,
The concentration of sodium thiosulphate.
Then we can know the mass of supplement C
= No . of moles of vitamin C Г— Molar mass of vitamin C
= Number of skin moles of I2 reacted with vitamin C Г—10 Г— Molar mass of nutritional C
= ( No . of moles of I2 produced - No . of skin moles of I2 reacted with Na2S2O3 ) Г—10 Г— Molar mass of supplement C
= ( No . of moles of KIO3 applied Г—3 - No . of moles Na2S2O3 Г·2) Г—10 Г— Large molar mass of vitamin C
Part A: Standardization of sodium thiosulphate solution
Mass of weighing bottle + solid potassium iodate(V) = 4. 48g
Mass of weighing bottle = 3. 96g...