An aqueous solution of orthophosphoric acid, H3PO4, has a measured density of 1.2089 g mL-1 and is 5.257 molal. The solution is 34.0% phosphoric acid. How many moles of H3PO4 are there in one liter of this solution?

In one liter of solution, there are 4.194 moles of H₃PO₄

Explanation:

A molal solution contains 1 mole of solute in 1 Kg of solvent.

A  aqueous 5.257 molal solution of H₃PO₄ will contain 5.257 moles of  H₃PO₄ in 1 Kg or 1000 g of water .

Molar mass of H₃PO₄ = 98 g/mol

Therefore mass of H₃PO₄ = number of moles * molar mass

mass of H₃PO₄ = 5.257 mol * 98 g/mol = 515.2 g

mass of solution = mass of solute + mass of solvent

mass of solution = 515.2 + 1000 = 1515.2 g

Volume of solution = mass of solution / density of solution

Volume of solution = 1515.2 / 1.2089 = 1253.4 mL

Molarity of solution = number of moles / volume (L)

Molarity of solution = 5.257 / 1.2534 L = 4.194 mol/L

Therefore, in one liter of solution, there are 4.194 moles of H₃PO₄