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Category: Engineering
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Experience:  Mechanical Engineering
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# How do I calculate the percentage of phosphorus in 85% phosphoric

### Resolved Question:

How do I calculate the percentage of phosphorus in 85% phosphoric acid?
Submitted: 4 years ago.
Category: Engineering
Expert:  ibosley replied 4 years ago.

ibosley :

Hello, I can answer this for you. You have to first look at the total molecular weight of phosphorus, which is H3PO4. Since H=1, P=98, and O=16 you simply add them together. H3PO4=(1*3)+(98)+(16*4)=165 Out of this weight Phosphorus accounts for 98/165, or 59.4% But since the solution is only 85% concentrated you have to multiply the two together, or .85*.549=51%

ibosley :

I hope this helps, thanks for using JustAnswer!

Customer:

Thanks, XXXXX XXXXX good sense to me.

ibosley, Master's Degree
Category: Engineering
Satisfied Customers: 93
Experience: Mechanical Engineering
Expert:  ibosley replied 4 years ago.
There was a mistake in my answer, I meant the total molecular weight of phosphoric acid is 165. The phosphorus accounts for 98/165 of it. Pleasure doing business with you.
Customer: replied 4 years ago.
You multiplied .85 by .549 ...?
you meant .85 by .594?
Customer: replied 4 years ago.
At any rate, I'm still seriously confused...
I understand the math that got us to this point - it just does't jive with what a major manufacturer of phosphoric acid says when it come to converting H3PO4 to P
http://www.potashcorp.com/media/PCS_phos_acid_manual.pdf
pg13
Expert:  ibosley replied 4 years ago.
.594*.85. My mistake twice, i'm on a roll tonight haha. I gave you the equation to calculate it based on grams per mol concentration, that manufacturer might do it differently, I would have to read into it more. But the two should be similar.
Customer: replied 4 years ago.
You might want to read into it more, the numbers are significantly different...
?
Expert:  ibosley replied 4 years ago.
Okay you finally wrestled the real answer out of me. The molar weight of Phosphorus is 31, not 98. 98 is the atomic weight of phosphoric acid. So 31/98 is .316, the same thing as your chart reads. So you simply take 85%X31.6%=26.9%

I don't think I've ever made this many mistakes on one problem in my life, but that is how it goes sometimes. If you have any more questions feel free to ask, I owe you one.
ibosley, Master's Degree
Category: Engineering
Satisfied Customers: 93
Experience: Mechanical Engineering

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