Titration of Vitamin C tablets
Prior to titration, Vitamin C samples were dissolved in dilute sulfuric acid, treated with a 60mL portion of 0.3 M KIO3 and excess KI.
Given equations:
(1) ascorbic acid + I2 + 2H2O <--> dehydroascorbic acid + 2I^- + 2H3O^+
(2) IO3^- + 5I^- + 6H3O^+ --> 3I2 + 9H2O
(3)I2 + 2S2O3^2- --> 2I^- + S4O6^2-
To find:
a) Thiosulfate consumed(mmol)
b) Excess I2 (mmol)
c) Ascorbic acid content (mmol)
d) Ascorbic acid conten (mg)
I am unsure how to go about finding these results -- i would think i would use a mol ratio from the given equations, but im confused with what equations to use ... any help would be GREATLY appreciated!
a. Thiosulfate consumed. Remember that molarity = moles/L OR mmoles/mL. So mmoles thiosulfate = M x mL. I assume you have the molarity and the mL of thiosulfate used.
b. The excess I2 is what was titrated with the thiosulfate in question a. So mmoles I2 = just 1/2 mmoles thiosulfate. You find that from the mole ratio in the I2/S2O3 equation.
c. How much I2 was present to react with vitamin C? That is 60 mL IO3^- x 0.3 M = 18 mmoles IO3^-. That produced 18 x 6 = 108 mmoles I or 54 mmoles of I2 (equation 2). Now subtract from that the excess I2 present from part b. That will give you the I2 that reacted with vitamin C. And since 1 mole vitamin C is equivalent to 1 mole I2 (equation 1), that will also be the mmoles of vitamin C.
d.You should be able to convert from mmols to mg.
Check my thinking.
thank you so much for your help!
To find the results for a) Thiosulfate consumed (mmol), b) Excess I2 (mmol), c) Ascorbic acid content (mmol), and d) Ascorbic acid content (mg), you will need to use the given equations and perform a series of calculations. Here's a step-by-step guide:
Step 1: Understand the titration and reactions involved. In this titration, vitamin C (ascorbic acid) is reacted with iodine (I2) in the presence of potassium iodide (KI) and potassium iodate (KIO3). Initially, the iodine reacts with thiosulfate (S2O3^2-) to form iodide ions (I^-) and tetrathionate ions (S4O6^2-).
Step 2: Calculate the number of moles of thiosulfate consumed (a). From equation (3), you know that 1 mole of I2 reacts with 2 moles of thiosulfate, so the number of moles of thiosulfate consumed is equal to half the number of moles of I2 added.
Step 3: Calculate the number of moles of excess I2 (b). From equation (1), you know that 1 mole of ascorbic acid reacts with 1 mole of I2. So, the number of moles of excess I2 is equal to the moles of I2 added.
Step 4: Calculate the number of moles of ascorbic acid (c). From equation (1), you know that 1 mole of ascorbic acid reacts with 1 mole of I2. So, the number of moles of ascorbic acid is equal to the moles of I2 added.
Step 5: Calculate the mass of ascorbic acid (d). To convert moles of ascorbic acid to mass, you need the molar mass of ascorbic acid. The molar mass of ascorbic acid is 176.12 g/mol. Multiply the number of moles of ascorbic acid (c) by the molar mass to get the mass in grams. To convert grams to milligrams, multiply by 1000.
Here's a summary of the calculations:
a) Thiosulfate consumed (mmol) = (moles I2 added) / 2
b) Excess I2 (mmol) = moles I2 added
c) Ascorbic acid content (mmol) = moles I2 added
d) Ascorbic acid content (mg) = (mass of ascorbic acid in grams) x 1000
By plugging in the appropriate values obtained from your experimental data into these equations, you will be able to calculate the desired results.
Note: Be sure to use appropriate units for the given quantities and follow the correct stoichiometry provided by the balanced equations.