Chemistry ! Need Help Please :"(

[Sweet_03]

Hello ,
i have this Chemistry thing that i cant do 
We've done an experiment to determine the Vitamin C Concentration in Fruit Juice.

* We added 30cm³ of Potassium iodid and 10cm³ of sulphuric acid to a conical flask
* Then we added 25cm³ of Potassium iodate(V) and 25cm³ of Apple Juice
* Then we Titrate against Sodium thiosulphate , using starch as the indicator
= the result was 5.15 cm³

Concentration Of :
* iodate = 0.005
* Sodium Thiosulphate = 0.01

OK So the Qs were :
Q1 Calculate The number of moles Of iodate (V) ions Present in 25cm³ of Potassium iodate(V)
n of Moles = Mc / 1000
= 0.001 * 25 / 1000 = 2.5 * 10^-5 Mol

Q2 Using the Equation
IO₃^- + 5I^- + 6H⁺ --> 3I₂ 3H₂O
Calculate the # of Moles Of iodine Produced
So  2.5 * 10^-5 Multiply By 3
=  7.5 * 10^-5 Mol

Q3 Using Your titre calculate the # of moles of thiosulphate that have reacted
n=cV
n= 0.01 * 5.15 = 0.0515 mol

Q4 Using This equation
I₂ = S₂O₃^2- --> S₄O₆^2- + 2I^-
Calculate the # Of moles of iodine that have reacted with the thiosulphate
It will be 0.0515 mol

Q5 Use Your ans. from part 2 & 4 to calculate the # of moles of iodine used to oxidise the Vitamin C

Q6 Calculate the # of moles of Vitamin C in 25cm³ of Apple Juice

Q7 Given that the molar mass of Vitamin C is 178 then Calculate the concentration of Vitamin C in the apple Juice in g dm^-3

How Can i do the last Three Q

[Sweet_03]

Plz Help Me 
i wud reallly appreciate it

[nid404]

it'll take some time....i'll answer it tom....cuz i have to study ffor mechanics...it'll be up tom for sure

[nid404]

can you tell me which paper it is from....

I'm kinda not sure abt the reaction...

if i know the 5th one, i can do the rest of them.....for that i think there needs to be another reaction

[Light]

the first ques was wrong at the first place.
no of moles=0.005 * 25/1000=1.25*10^-4.

Q2:ans in Q1 *3 =3.75*10^-4

Q3:0.01*5.15/1000=5.15*10^-5
Q4 answer as Q3.
actually very easy for Q5.for u just subtract answer in Q2 with Q4.cause the remaining not reacted with thiosulphate will oxidise vitamin c. Ans=3.235*10^-4.

Ans in Q6 same as Q5.

Q7:In 25 cm3 u have 3.235*10^-4 mol.In 1000 cm3 u have 0.01294 mol dm-3.*RMM(178)
Ans=2.30 gdm-3.



practical is easy if u get the flow.Light's Copyright.

[Sweet_03]

Thank You Very Much Light
i think i neeed more practice with these Qs