Electrode Potential: Manganate(VII) vs Dichromate(VI) for Fe(II) Titration

In summary, manganate(VII) is preferred over dichromate(VI) for titration with Fe(II) in volumetric analysis due to its sharper color change and higher emf of reaction. Additionally, using dichromate may result in interference from the slightly soluble iron chromates. The use of HCl with dichromate would result in a green solution, while using H2SO4 with manganate would result in a mostly colorless solution.
  • #1
Kushal
438
1

Homework Statement



Suggest why manganate(VII), rather than dichromate(VI) is used to titrate with Fe(II) in volumetric analysis.

The Attempt at a Solution



i have figured out 2 possible answers but both may not be correct...

1. the colour change is sharper with manganate (purple to mostly colourless) while for dichromate it is orange to green... I'm not quite sure about it though...

2. The emf of the reaction with manganate(+0.75V) is higher than that for dichromate(+0.56V). But that shouldn't mean that the rate of reaction is faster, right?


i would have preferred dichromate because then i could use HCl as acid?! which i guess is more available than H2SO4... i don't know :-S
 
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  • #2
What about solubility of chromates/dichromates?
 
  • #3
If you use dichromate and HCl, what color would all of the products be?
 
  • #4
i think dichromates/chromates are quite soluble. i remember a practical we did at school to find its Ksp and the solubility in water was high if I'm not wrong.

the solution will become green!
 
  • #5
Ag2CrO4 is soluble weakly enough to be used for endpoint detection in Mohr method. I don't have exact tables here, but intuition tels me that iron chromates will be weakly soluble and their precipitation may to some extent interfere with the redox reaction.

Cr3+ is green, that's correct. Fe3+ is sligthly yellow. Will you be able to see added excess of dichromate? Compare it with the situation in the permanganate case.
 
  • #6
yeah that makes sense for the colour when chromate is added in excess!
 

1. What is electrode potential?

Electrode potential is a measure of the tendency of an electrode to gain or lose electrons when in contact with a solution containing ions of the same metal.

2. How is manganate(VII) different from dichromate(VI)?

Manganate(VII) and dichromate(VI) are both transition metal ions that can be used as oxidizing agents in a titration. However, manganate(VII) has a higher electrode potential and is a more powerful oxidizing agent than dichromate(VI).

3. Why is Fe(II) used in this titration?

Fe(II) is a commonly used reducing agent in titrations because it can easily be oxidized to Fe(III), which can then be titrated with an oxidizing agent like manganate(VII) or dichromate(VI).

4. How does the electrode potential of manganate(VII) and dichromate(VI) affect the titration of Fe(II)?

The higher electrode potential of manganate(VII) means that it can readily oxidize Fe(II) to Fe(III), making it a more efficient and accurate titrant than dichromate(VI) in this particular titration.

5. What factors can affect the accuracy of this titration?

The accuracy of this titration can be affected by factors such as the concentration and purity of the manganate(VII) or dichromate(VI) solution, the concentration and purity of the Fe(II) solution, and any interfering substances that may be present in the solution being titrated.

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