4.77 x 10^30 hydrogen cations were found in a solution. How many grams of phosphoric acid were dissolved?

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gsenviro | College Teacher | (Level 1) Educator Emeritus

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Phosphoric acid has a chemical formula of H3PO4.

That means, each mole of phosphoric acid contains 3 moles of hydrogen atoms. Also, each mole of a substance contains an Avogadro's number of atoms or 6.023 x10^23 atoms.

Here, we have 4.77 x 10^30 atoms of hydrogen.

We can calculate the moles of hydrogen using the knowledge of Avogadro's number.

Hence, moles of hydrogen = (4.77 x 10^30)/(6.023 x 10^23) = 7.92 x 10^6 moles.

Using the chemical formula of phosphoric acid, 

3 moles of hydrogen atoms are present in 1 mole of phosphoric acid.

7.92 x 10^6 moles are present in 2.64 x 10^6 moles of phosphoric acid (= 7.92 x 10^6 / 3)

The molar mass of phosphoric acid is 98 grams.

Therefore, the amount of phosphoric acid that was dissolved = 7.92 x 10^6 x 98 gm 

= 2.59 x 10^8 gm.

Hope this helps.