Question

Найти массовую и мольную долю фосфорной кислоты, а также нормальность раствора ортофосфорной кислоты, полученного растворением 49 г. H3PO4 в 451 г. воды (плотность раствора равна 1,25 г/мл).

Answer 1

Масса конечного раствора,после добавление кислоты в воду:
49 + 451 = 500

ц(массовая доля)
49/500 * 100 = 9.8 %

мольная доля 
 х = 10 * 9.8 * 1.25/ 98 = 1.25/2 = 1.25 молярный раствор

500 ----------------- 0.5
а 1000------------- 1 , 1 нормальный раствор

Answer 2

Finding Mass and Molar Fraction of Phosphoric Acid

To find the mass and molar fraction of phosphoric acid, as well as the normality of the solution obtained by dissolving 49g of H3PO4 in 451g of water (with a solution density of 1.25g/ml), we can use the provided information and the molar mass of phosphoric acid.

1. Mass Fraction of Phosphoric Acid: - The mass fraction of phosphoric acid can be calculated using the formula: \[ \text{Mass Fraction (\%)} = \frac{\text{Mass of solute}}{\text{Total mass of solution}} \times 100 \] - Substituting the given values: \[ \text{Mass Fraction (\%)} = \frac{49g}{49g + 451g} \times 100 \] \[ \text{Mass Fraction (\%)} = \frac{49}{500} \times 100 \] \[ \text{Mass Fraction (\%)} = 9.8\% \] - Therefore, the mass fraction of phosphoric acid is 9.8%.

2. Molar Fraction of Phosphoric Acid: - The molar fraction of phosphoric acid can be calculated using the formula: \[ \text{Molar Fraction} = \frac{\text{Moles of solute}}{\text{Total moles of solute and solvent}} \] - To calculate the moles of phosphoric acid, we need to know the molar mass of phosphoric acid, which is 98 g/mol. - The moles of phosphoric acid can be calculated as: \[ \text{Moles of H3PO4} = \frac{\text{Mass of H3PO4}}{\text{Molar mass of H3PO4}} = \frac{49g}{98g/mol} = 0.5 mol \] - The moles of water can be calculated as: \[ \text{Moles of H2O} = \frac{\text{Mass of H2O}}{\text{Molar mass of H2O}} = \frac{451g}{18g/mol} = 25.06 mol \] - The total moles of solute and solvent: \[ \text{Total moles} = \text{Moles of H3PO4} + \text{Moles of H2O} = 0.5 mol + 25.06 mol = 25.56 mol \] - The molar fraction of phosphoric acid: \[ \text{Molar Fraction} = \frac{0.5 mol}{25.56 mol} \approx 0.0196 \] - Therefore, the molar fraction of phosphoric acid is approximately 0.0196.

3. Normality of the Solution: - The normality of the solution can be calculated using the formula: \[ \text{Normality} = \frac{\text{Number of equivalents}}{\text{Volume of solution in liters}} \] - Since orthophosphoric acid (H3PO4) is a triprotic acid, it can donate three equivalents of H⁺ ions per molecule. - The number of equivalents of H3PO4 in 49g can be calculated as: \[ \text{Equivalents} = \frac{\text{Mass of H3PO4}}{\text{Equivalent mass of H3PO4}} = \frac{49g}{98g/equiv} = 0.5 equiv \] - The volume of the solution can be calculated as: \[ \text{Volume of solution} = \frac{\text{Mass of solution}}{\text{Density of solution}} = \frac{500g}{1.25g/ml} = 400ml = 0.4L \] - The normality of the solution: \[ \text{Normality} = \frac{0.5 equiv}{0.4L} = 1.25 N \] - Therefore, the normality of the solution is 1.25 N.

In summary, the mass fraction of phosphoric acid is 9.8%, the molar fraction of phosphoric acid is approximately 0.0196, and the normality of the solution is 1.25 N.