Question

An Aqueous solution of orthophosphoric acid has a measured density of 1.2089 grams/ mL-1 and is 5.257 molal. How many moles orthophosphoric acid are in 1 liter of this solution?

Answer 1

find mass:

density=mass/volume

convert to moles:

moles=mass/molar mass

Answer 2

use the density to find the mass of one liter: (1 L)*(1 g/1.2089 mL)*(10^3 mL/ 1 L)*(1 kg/10^3 g) = .8272 kg

next, convert molals to moles: (5.257 mole solute/kg solvent)*(.8272 kg) = 4.378 moles