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sarah1004
Nov 24, 2009, 09:04 PM
standardization of KMnO4
Mass of H2C2O4.2H2O(MW=126g/mol),g------->0.25
Initial buret reading, mL-------------------------->0
Final buret reading, mL--------------------------->43
Volume of KMnO4 solution used, mL------------>43
Moles ofo oxalic acid used------------------------>0.002
Moles of KMnO4 used(refer to the equation)---->??
Molarity of KMnO4 solution------------------------>??
2MnO4^- + 5C2O4^2- + 16H^+ ----------------> 2Mn^2+ + 10CO2 + 8H2O

Mass of sample, g---------------------------------->0.8
Initial buret reading, mL--------------------------->0
Final buret reading, mL---------------------------->23
Volume of KMnO4 used, mL----------------------->23
Moles of KMnO4 used------------------------------>3.0
Moles of iron in sample---------------------------->??
Mass of iron in the sample, g---------------------->??
Percent of iron in the sample---------------------->??
MnO4^- + 5Fe^2+ + 8H^+ -----------------------> Mn^2+ + 5Fe^3+ + 4H2O

I couldn't find that question marks answers.
Thank you!

Unknown008
Nov 25, 2009, 10:11 AM
1. Ok, you have the number of moles of oxalic acid used.

You know from your equation that 5 moles of oxalic acid react with 2 moles of MnO4^-.

Can you now guess the number of moles of MnO4^-?

2 C2O4^2- -> 5 MnO4^-
0.002 C2O4^2- -> ? MnO4^-

Then, you know the number of moles of MnO4^- in 43 cm^3. Find the number of moles in 1000 cm^3.

2.
Is the concentration of KMnO4 130 M!

Same thing here. You know from your equation that 5 moles of iron (II) react with one mole of MnO4^-.
1 MnO4^- -> 5 Fe^2+
3.0 MnO4^- -> ? Fe^2+
[provided the concentration of MnO4^- is 130 M]

Then, find the mass of that Fe^2+, with the AW of Fe.

The fraction of Fe^2+ in the sample is the weight due to Fe^2+ over the total weight. The percentage is that fraction, multiplied by 100%.