Chemistry - Volumetric Analysis I can't do this

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Discussion Overview

The discussion revolves around the calculation of the number of water molecules (x) in the hydrated salt FeC2O4.xH2O, based on a volumetric analysis involving titration with KMnO4. Participants explore the stoichiometric relationships and calculations necessary to determine x from given mass and concentration data.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant presents a problem involving the determination of x in FeC2O4.xH2O, providing specific mass and titration data.
  • Another participant questions how the concentration of the C2O4 anion was known and suggests using the stoichiometric equation for the reaction to deduce further information.
  • A third participant confirms the calculation of moles in the 25 mL sample and suggests calculating the total moles in the 250 mL solution to find the molar mass of the hydrate, which is necessary to determine x.
  • A link to an external resource is provided, presumably for additional reference or information.

Areas of Agreement / Disagreement

Participants generally agree on the approach to calculate the number of moles and the need for stoichiometric relationships, but there is no consensus on the method to find the concentration of the C2O4 anion or the subsequent steps to determine x.

Contextual Notes

There are unresolved assumptions regarding the stoichiometric coefficients in the reaction and the specific method to calculate the molar mass of the hydrate, which could affect the determination of x.

rhuthwaite
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How do I find x in FeC2O4.xH2O. I am told that this is a hydrated salt of 1.75g and was dissolved in acid and made up to 250ml. A 25mL sample of this solution required 29.15mL of standardised 0.0200mol/L KMnO4 solution for complete oxidation.

I worked out n(MnO4-) = cv = 5.83 x 10^-4 moles
and n(C2O4^2-) = 1.4575 x 10^-3 moles
and c(C2O4^2-) = n/v = 0.0583 molL-1
I just don't know how to find x
 
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How would you know of the concentration of the C2O4 anion already? You need to employ the stoichiometric equation for the pertinent reaction and then deduce things from there with the mole value you have for the titrant KMnO4.
 
You know number of moles in 25 mL (you have calculated it correctly, BTW), calculate number of moles in 250 mL. Now, number of moles is mass/molar mass - you know mass, you know number of moles, you can calculate molar mass of hydrate. Molar mass is all you need to find x.
 

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