[AleggsMac]

Hey there!

I hope this is the right forum, but it's due to massive desperation because I'm completely confused. I would go to a Chem tutor in uni, but I can't until my tutorial session, which is also the deadline for my work . My Chemistry lecturer has also been away in the week I've had to do this, so we've not had any lectures after which I could ask for help.

I've recently done a redox titration that went as such:

1. Dissolve Vitamin C tablet in 0.04L Sulphuric Acid (0.5mol/L)
2. Add 0.5g Sodium Hydrogen Carbonate
3. Add 25mL KIO3 solution (0.03mol/L) and 1.5g KI
4. Add another 5ml of Sulphuric Acid and another 0.5g Sodium Hydrogen Carbonate
5. Fill burette with Sodium Thiosulphate and titrate the above mixture

Okay, so did all that, and got 3 readings that averaged at 20ml of Sodium Thiosulphate being added.

I was also given 3 equations

a) IO3^- + 5I^- + 6H+ -------> 3I2 +3H2O
b) I2 + C6H8O6 + H2O -----> C6H8O7 + 2I^- + 2H^+
c) I2 + 2S2O3^2- -------> 2I^- + S4O6^2-

Now I've got some questions, which I would like someone to help me with, possibly take me through step by step.

1) Calculate the number of mol in mmol of Iodine initially
2) Calculate mmol of Iodine remaining
3) Calculate Total mmol of Ascorbic Acid
4) Total Ascorbic Acid in mg

So far for 1) I've got 0.75mmol. I did this by taking the concentration and volume of IO3 and getting the mol from that, then multiplying that by 1,000 to get mmol. (0.03 X 0.025 = 7.5 X 10^-3 X 1000 = 0.75mmol)

Can someone tell me if I'm right or wrong? I think it's wrong, and even if I'm correct, I have no idea how to figure out the rest of the questions. I would just like some step by step guidance, so that I can understand it for future, not just get given the answers and then copy them down.

I really hope someone can help, I'm so useless with Chemistry. I'm not looking for answers outright, I'd like a step by step guide on how to figure out the questions above.

Thanks!

[Borek]

Every step here is a simple and basic stoichiometry - so you have to follow stoichiometric coefficients.

So far you have calculated number of milimoles of iodate, not iodine.

How many moles of iodine are produced per mole of iodate present?

[AleggsMac]

3 moles of Iodine from one mole of Iodate?