Hello,
I am working on vanadium flow batteries, and I am planning to make 250mL of: 1.2M VOSO4 + 3.0M H2SO4. from: VOSO4.xH2O , concentrated sulfuric acid, and DI water.
I have vanadium in the form of: http://www.sigmaaldrich.com/catalog/product/aldrich/233706?lang=en®ion=AE
To prepare the solution, I have used the certificate analysis for the vanadium material we have from: http://www.sigmaaldrich.com/Graphics/COfAInfo/SigmaSAPQM/COFA/23/233706/233706-BULK_______MKBR6238V_.pdf
and got the percentage of vanadium to be %V =22.7%,
I then calculated the total amount of x to be 3.409 in the VOSO4.xH2O compound, as shown in my attached calculations for vanadium.
The total MW of VOSO4.xH2O was calculated to be 163+ (3.409)(18.015) =224.413 g/mol.
and finally 67.324g of the VOSO4.xH2O would be required for a 250ml solution. (CALCULATIONS ARE ATTACHED IN THE PICS).
For the sulfuric acid, I have it concentrated by sigma aldrich as follows:
http://www.sigmaaldrich.com/catalog/product/sial/30743?lang=en®ion=AE
with a w.p. of 96.2% as per the certificate analysis provided by sigma aldrich, and p = 1.84 g/mol, MW=98.08 g/mol.
I used the molarity calculator from this link: http://www.sigmaaldrich.com/chemistry/stockroom-reagents/learning-center/technical-library/molarity-calculator.html
, and found that for 3M in 250ml total solution volume, we need 41.557ml to be added to 62.5ml of DI water slowly. And then, more DI water is added slowly to reach 250ml.
However, the volume of the water in the hydrate needs to be accounted for, and was calculated to be 18.423 ml of water in the 67.324 g of the VOSO4.xH2O, as per this equation: (desired_molarity) x (desired final volume of solution) x (No. of H2O molecules) x 18.015 = ml H2O contributed by hydrated compound.
Thus, only 231.576 ml (250ml - 18.423ml) of DI water needs to be added during the sulfuric acid preparation.
Thus, My proposed procedure should be as follows (in a fume hood and PPE):
Based on the attached 2 sheets of my calculation:
1. Prepare 62.5mL of DI water.
2. Isolate 41.557mL of h2so4.
3. Add 41.557 ml h2so4 to 62.5ml DI water slowly.
4. The water content in the VOSO4 hydrate we have was calculated to be 18.423ml (assuming density of h2o is 1g/ml). Thus, Add 231.576 ml only (250ml - 18.423ml) of DI water.
5. Add 67.324g of VOSO4 hydrate to the solution slowly, and the final solution should have a total volume of 250ml.
6. Stir and dissolve.
I am a little puzzled, and need confirmation that the method is accurate and reliable:
1. Will this method give us accurately 250mL of 1.2M VOSO4 + 3.0M H2SO4?
2. Is the molarity of the vanadium ion correct in the final solution?
3. Is the molarity of the h2so4 correct in the final solution?
4. Since we are dissolving hydrated vanadium in aqueous sulfuric acid, will that have any affect on the final concentrations of V4 and H2SO4 in the mixture, due to the added water please?
Much Thanks,
Ibrahim
http://www.sigmaaldrich.com/catalog/product/aldrich/233706?lang=en®ion=AE
http://www.sigmaaldrich.com/Graphics/COfAInfo/SigmaSAPQM/COFA/23/233706/233706-BULK_______MKBR6238V_.pdf
http://www.sigmaaldrich.com/catalog/product/sial/30743?lang=en®ion=AE
http://www.sigmaaldrich.com/chemistry/stockroom-reagents/learning-center/technical-library/molarity-calculator.html
The common practice to prepare vanadium(IV) solution of precise concentration implies the potentiometric titration of the final solutions. The amount of x H2O in VOSO4 hydrate varies upon storage from 4 to 6. The concern about dilution of H2SO4 by xH2O is right: you can account for it while adding DI water.
Hi Dr. Chi,
Thanks a lot for your answer.
Sigma Aldrich states the molecular weight of the VOSO4, without the H2O weight. So, I looked up the percentage of vanadium they provided from the certificate of analysis provided by sigma aldrich, and used that to calculate the amount of H2O, and then based on that, I calculated the molecular weight of the compound.
Thus, I think that the precision of my molecular weight calculations are dependent on the precision of the percentage value provided in the certificate of analysis by sigma aldrich.
And yes, it is stable in H2SO4.
Much Thanks,
Ibrahim
Hi Nataliya,
Thank you very much. Potentiometric titration is surely interesting. For that, I would need a potentiometric titrator.
However, do you think it would be possible to perform the potentiometric titration using a simple 3 electrode cell, and a potentiostat. I will use carbon electrodes for the working and counter electrodes. an ag/agcl for the ref electrode, a pipette and a burette.
Do you have any document/ link? or can you recommend me please the name of a book that can guide me on the basic lab procedure? such that it could be adapted to my vanadium case, as I am totally new to such a topic.
Thanks a lot for your help!
Ibrahim
Yes, you can use potentiostat. You need just two-electrodes cell to perform the titration, however it is necessary to stirr the solution and wait until the potential value is stable. As for the reference, you can find information about "potentiometric procedure" in any book of electrochemical methods.
Dear Nataliya,
Hii Nataliya Iam the new one in VRFB so i need your assist , could you tell me
(1)how to prepare vanadyl sulfate electrolyte?
(2) after preparation of electrolyte how V4+ oxidation state turns into other oxidation states of vanadium i.e.V2+,V3+ and V5+.is there any method by which VOSO4 reacts with acid to convert into other oxidation states.
thanks and regards
Harsh
Dear all,
can any body tell me that while performing the experiment initially we have V4+ electrolyte in both tanks then on charging the V4+ gets oxidized into V5+ and V4+ gets reduced into V3+. So there would not be pure V5+ there would also V4+in tank so how do we separate the V4+ from V5+ and V4+ from V3+ in both tanks. Is there any method to separate both these electrolyte from their different oxidation state.
with regards
Harsh
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