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titration with potassium manganate and iron practical watch

1. Okay so first I need to make a standard solution with 5 iron tablets and sulphuric acid. This needs to go in the volumetric flask I think. I am using potassium manganate and this will go in the burette. From my dilution calculation,w which I will show you below, I have worked out that I need to put 25cm3 in the burette for every titration I think. Because of this, I can conduct 10 titrations from one standard solution.

These are my calculations but I don't know how to put them into a practical:

So first I worked out the volume of potassium manganate when one iron tablet was used, and found that the volume of potassium manganate that would be put in burette was too small. My teacher told me to increase the number of iron tablets used or decrease the concentration of MnO4- to increase volume of MnO4-

Mr of C4H2FeO4 (the iron tablet is ferrous fumurate (iron)): 169.8
I am given that the mass of one iron tablet is: 210g but I convert this to mg as told by my teacher so 210*10-3 mg
Moles of Fe2+: 1.236749*10-3 (this would be in 250cm3 because that is how much can fit in the volumetric flask, which I have in my notes)
Moles of Fe2+ in 25cm3 (i think this is done for the standard solution so this should be in the pipette): so i divided the moles of fe2+ by 10: 1.2367494*10-4
Moles of MnO4- (this is the molar ratio which is *5 ): 2.47398*10-5
Volume of MnO4- (I am given that the concentration of MnO4- is 0.02): 1.23674*10-3 so this would be 1.23674 dm3

so then i increased the number of tablets (the maximum number of tablets per titration i can use is 5):
moles of fe2+: (0.21*5)/169.8=6.183745583*10-3
moles of fe2+ in 25cm3: 6.183745583*10-4
moles of MnO4-:1.236749117*10-4 cm3
volume of MnO4-:6.183745585*10-3=6.18374558 dm3 so this is still too small.

then I did the dilution calculation:
Dilution of MnO4-: 1/2 * 1/2 * 0.02 (the concentration given this is)= 2.5 *10-3 mol dm3
=24.734 cm3

then my teacher gave me the ratio
1:4
?:250
25:100
my teacher said 25 (i suppose cm3) in the pipette and 100(cm3) in the flask
and then add of the solution to the burette.

Have I even done the dilution calculation correctly and what exactly does the ratios mean. please help
actually now that i have done the dilution calculation i think have multiplied the concentration of 0.02 by 1/8 so 1/2*1/2*1/2*0.02 which gives me 2.5*10-3
does this mean the ratio is 1:8 and what does this mean for the volumes. i haven't replaced this with my original calculation because I don't even know if this is even correct. this is so much harder!!
2. Those are big iron tablets.

Why are you saying you are using potassium manganate when you give the formula for permanganate?
3. (Original post by Maker)
Those are big iron tablets.

Why are you saying you are using potassium manganate when you give the formula for permanganate?
no i am using potassium manganate (KMnO4) but obviously the MnO4- ions are the ones I am interested in.
do you understand how i would dilute the potassium manganate ?
4. (Original post by esmeralda123)
no i am using potassium manganate (KMnO4) but obviously the MnO4- ions are the ones I am interested in.
do you understand how i would dilute the potassium manganate ?
Potassium manganate has the formula K2MnO4, potassium permanganate has the formula KMn04, they are different chemicals.

Yes, I think I understand what you are doing, you are trying to find how much ferric II is in the iron tablets by titrating it with KMnO4. The MnO4- ion which is purple oxidises the ferric II to ferric III and the MnO4- is reduced to Mn2+, which is a very pale pink.

I find what you have written rather confusing and you only need two significant decimal places in your calculations.

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Updated: October 29, 2017
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