What is the molarity of concentrated phosphoric acid if this solution is 85.5% H₃PO₄ by weight and it has a density of 1.70 g/mL?

Question

Quizplus · Accepted Answer

To find the molarity of the concentrated phosphoric acid, we first need to understand that the formula given in the question, "H₃PO₄," is a typographical error. The correct chemical formula for phosphoric acid is $H_3PO_4$. Given that the solution is 85.5% $H_3PO_4$ by weight and has a density of 1.70 g/mL, we can calculate the molarity as follows:1. Calculate the mass of $H_3PO_4$ in 1000 mL of solution:$$ \text{Density} = 1.70 \, \text{g/mL} $$$$ \text{Volume} = 1000 \, \text{mL} $$$$ \text{Mass of solution} = 1.70 \, \text{g/mL} \times 1000 \, \text{mL} = 1700 \, \text{g} $$2. Calculate the mass of $H_3PO_4$ in the solution:$$ \text{Mass of } H_3PO_4 = 1700 \, \text{g} \times 0.855 = 1453.5 \, \text{g} $$3. Convert the mass of $H_3PO_4$ to moles (molar mass of $H_3PO_4$ = 98 g/mol):$$ \text{Moles of } H_3PO_4 = \frac{1453.5 \, \text{g}}{98 \, \text{g/mol}} = 14.83 \, \text{mol} $$4. Calculate the molarity of the solution:$$ \text{Molarity} = \frac{\text{Moles of solute}}{\text{Volume of solution in liters}} = \frac{14.83 \, \text{mol}}{1 \, \text{L}} = 14.8 \, \text{M} $$Therefore, the molarity of the concentrated phosphoric acid is 14.8 M.

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