Question

A 20.0 % by mass solution of phosphoric acid (H 3PO 4) in water has a density of 1.114 g/mL at 20°C. What is the molarity of this solution?

Answer 1

Answer:

2.28 M

Explanation:

Step 1: Given data

Percent by mass (%m/m): 20.0 %

Density (ρ): 1.114 g/mL

Step 2: Calculate the percent by volume (%m/v)

We will use the following expression.

$\% m/v = \% m/m \times \rho = 20.0 \% \times 1.114g/mL = 22.3 g \% mL$

Step 3: Calculate the moles of solute in 100 mL of solution

The molar mass of phosphoric acid is 97.99 g/mol. The moles corresponding to 22.3 g are:

$22.3g \times \frac{1mol}{97.99g} = 0.228mol$

Step 4: Calculate the molarity of the solution

0.228 moles of solute are in 100 mL (0.100 L) of solution. The molarity of the solution is:

$M = \frac{0.228mol}{0.100L} =2.28 M$