Question

Concentrated phosphoric acid is 90% H3PO4 by mass and the remaining mass is water. The

molarity of H3PO4 in 90% H3PO4 is 12.2 M at roomtemperature.

a. What is the density of this solution at room temperature? 1.33 g/mL

b. What volume (in mL) of this solution is needed to make a 1.00 L solution of a 1.00 M

phosphoric acid? 82.0 mL​

Answer 1

Concentrated phosphoric acid is 90% by mass and the remaining mass is water. The molarity of H₃PO₄ is 12.2 M at room temperature.

we have to find

a. the density of this solution at room temperature.

b. the volume (in mL) of this solution is needed to make a 1.00 L solution of 1.00 M phosphoric acid.

solution : using formula, molarity = percentage by weight × 10 × density/molecular weight

here molarity = 12.2 M

molecular weight = 1 × 3 + 31 + 4 × 16 = 34 + 64 = 98g/mol

percentage by weight = 90%

so, 12.2 = 90 × 10 × density/98

⇒12.2 × 98/900 = density

⇒density = 1.33 g/mL

Therefore the density of this solution at room temperature is 1.33 g/mL

using formula, M₁V₁ = M₂V₂

here, M₁ = 12.2 M, V₁ = ? , M₂ = 1M and V₂ = 1L

⇒12.2 × V₁= 1 × 1

⇒V₁ = 1/12.2 L = 0.008196 L = 81.96 ml ≈ 82 mL

Therefore 82ml volume of this solution is needed to make 1.00L solution of a 1.00 M