Question

Vitamin C or ascorbic acid, C6H8O6, is present in many fruit juices and vitamin tablets. In testing a commercial vitamin tablet the ascorbic acid is reacted with excess iodine and the amount of 1₂ remaining is determined with sodium thiosulfate (Na2S2O3). In one analysis a 1500 mg vitamin tablet was dissolved in water and treated with 53.20 mL of 0.1030 mol/L 1₂ according to the equation C6H8O6 (s) + 1₂ (aq) -> C6H6O6 (aq) + 2HI (aq) (Equation 1) After all the ascorbic acid had reacted, the excess I2 was reacted with 27.54 mL of 0.1153 M Na2S₂O3 according to 12 (aq) + 2Na2S₂O3(aq) (a) How many grams of ascorbic acid are in the vitamin tablet? (b) What is the percentage of vitamin C in the vitamin tablet? 2Nal (aq) + Na2S406 (aq) (Equation 2)​

Answer 1

To determine the amount of ascorbic acid (vitamin C) in the vitamin tablet, we can use the information provided in the chemical reactions and the data given. Here are the steps to calculate the grams of ascorbic acid and the percentage of vitamin C in the tablet:

(a) Calculate the moles of iodine (I2) reacted with ascorbic acid:

From Equation 1, we can see that one mole of ascorbic acid reacts with one mole of iodine (I2). Therefore, the moles of I2 reacting with ascorbic acid are equal to the moles of I2 added initially.

Moles of I2 = (0.1030 mol/L) * (0.05320 L) = 0.0054796 mol I2

(b) Calculate the moles of sodium thiosulfate (Na2S2O3) reacting with excess iodine:

From Equation 2, we can see that one mole of iodine (I2) reacts with two moles of sodium thiosulfate (Na2S2O3). Therefore, the moles of Na2S2O3 reacting with I2 are half of the moles of I2.

Moles of Na2S2O3 = (0.0054796 mol I2) / 2 = 0.0027398 mol Na2S2O3

(c) Calculate the moles of excess I2:

The moles of excess I2 are the initial moles of I2 minus the moles reacted with ascorbic acid.

Moles of excess I2 = (0.1030 mol/L) * (0.02754 L) = 0.00283762 mol I2

(d) Calculate the moles of ascorbic acid reacted:

The moles of ascorbic acid reacted are equal to the moles of excess I2 (since the reaction is 1:1 between I2 and ascorbic acid).

Moles of ascorbic acid = 0.00283762 mol

(e) Calculate the mass of ascorbic acid in the tablet:

Now, we can use the molar mass of ascorbic acid (C6H8O6) to find the mass:

Molar mass of ascorbic acid (C6H8O6) = (612.01 g/mol) + (81.01 g/mol) + (6*16.00 g/mol) = 176.08 g/mol

Mass of ascorbic acid = (0.00283762 mol) * (176.08 g/mol) = 0.4997 g

(a) The amount of ascorbic acid in the vitamin tablet is approximately 0.4997 grams.

(b) To calculate the percentage of vitamin C in the tablet, divide the mass of ascorbic acid by the total mass of the tablet and multiply by 100:

Percentage of vitamin C = (0.4997 g / 1500 mg) * 100% = 33.31%

The percentage of vitamin C in the vitamin tablet is approximately 33.31%.