[born2dive00]

Hello Everyone I am not a chemist nor have much experience in the formulas. I have tried to solve this and I can not get it to work out.

I am trying to find the Ph of 8.10581454g of 85% phosphoric acid in 18927.1ml of water.

Please help I have tried the calculators but unfortunately i can not seem to get an accurate result.


Here is my math
Ok can some one please tell me if I did this right

I have 8.105807928 grams of 85% Phosphoric acid. Now Phosphoric acid has 97.995287 molecular mass

So if i divide 8.105870928 by 97.995287 I get .082716304 moles is this correct?

Then since I have 18.9271 L

So if I take .082716304 and divide by 18.9271 i get .00437 for the concentrate is this correct?

Now when I put this into the ph calculator I am getting 2.47 ph is this correct?

Please let me know what the Ph would be on this solution.

Thank you
Brad

[born2dive00]

I Know I am not right, I have come up with 2 different ph levels 1.62 and 2.32 and the last attempt i just did i got a ph of 2.53

Please help.

Brad

[Borek]

I am trying to find the Ph of 8.10581454g of 85% phosphoric acid in 18927.1ml of water.

Have you really measured the mass and the volume with such a high accuracy?

First step is to find the molar concentration of the acid.

[born2dive00]

Hello Borek Excel sheet, I have scales to 1mg resolution which I know is no where near this accurate as excel is telling me.

I think I have calculated it correctly now but I am not sure. I came up with .082712 for the concentration, which would put the ph out at 1.6?

Does this sound correct?

Please help.

Brad

I am trying to find the Ph of 8.10581454g of 85% phosphoric acid in 18927.1ml of water.

Have you really measured the mass and the volume with such a high accuracy?

First step is to find the molar concentration of the acid.

[born2dive00]

Ok can some one please tell me if I did this right

I have 8.105807928 grams of 85% Phosphoric acid. Now Phosphoric acid has 97.995287 molecular mass

So if i divide 8.105870928 by 97.995287 I get .082716304 moles is this correct?

Then since I have 18.9271 L

So if I take .082716304 and divide by 18.9271 i get .00437 for the concentrate is this correct?

Now when I put this into the ph calculator I am getting 2.47 ph is this correct?

[Borek]

So if i divide 8.105870928 by 97.995287 I get .082716304 moles is this correct?

In general your logic here and in the next step looks mostly correct, but you have missed one important thing - you don't have 8.1 g of phosphoric acid, you have 8.1 g of a solution that contains 85% of phosphoric acid.

[born2dive00]

Hello Borek

So if i take the 8.1g of phosphoric acid solution and mutiply it by .85  (85%) i get 6.8899902888g of phosphoric acid. Now if I take this number and divide it by 97.995287 I get (according to my calcuations) 0.07030940466 Moles

Now if i divide that by the 18.9271 L i get a concentration of 0.00371474788 DOES THIS LOOK CORRECT??

When I put this into my ph calculator i get a ph of 2.53 does this sound about right?

Please let me know
Thanks
Brad

So if i divide 8.105870928 by 97.995287 I get .082716304 moles is this correct?

In general your logic here and in the next step looks mostly correct, but you have missed one important thing - you don't have 8.1 g of phosphoric acid, you have 8.1 g of a solution that contains 85% of phosphoric acid.

[Borek]

Please round down these numbers, they look awfully wrong, 4 digits are perfectly enough.

So if i take the 8.1g of phosphoric acid solution and mutiply it by .85  (85%) i get 6.8899902888g of phosphoric acid. Now if I take this number and divide it by 97.995287 I get (according to my calcuations) 0.07030940466 Moles

Now if i divide that by the 18.9271 L i get a concentration of 0.00371474788 DOES THIS LOOK CORRECT??

Yes, that's OK, although 0.003715 M would be completely enough (probably even that is way too accurate).

When I put this into my ph calculator i get a ph of 2.53 does this sound about right?

I got 2.57/2.58 (depending on whether I account for ionic strength of the solution or not), close enough.