Question

A phosphate-ion (PO43-) level in a water sample is 93.1 ppm (or mg/L). What is the concentration of this phosphate sample in molarity? Density of water is 1 g/mL Note: In the field of water quality, ppm and mg/L are the same unit.

Answer 1

The molarity of a solution can be calculated by dividing the number of moles of solute by the volume of the solution in liters. To calculate the number of moles of solute in a solution, we first need to find the mass of the solute.

Since the concentration of the phosphate sample is given in mg/L (ppm), we can convert this to grams by multiplying by 0.001:

93.1 mg/L x 0.001 g/mg = 0.0931 g/L

Next, we can find the number of moles of solute by dividing the mass of solute by its molar mass:

0.0931 g ÷ (1 mol/94 g) = 0.000989 mol/L

Finally, we can find the molarity of the solution by dividing the number of moles of solute by the volume of the solution:

0.000989 mol ÷ (1 L) = 0.000989 M