Question

Phosphoric Acid is usually obtained at an 85% phosphoric acid solution, by mass. If this solution is 15 M, what is the density of the solution? What is its MOLALITY?

Answers

bobpursley
Assume 1000 grams of solution.
then you have 850 grams phosphoric acid, and 150 grams of water.

15M=850/molmassH3PO4 / volumeinL

solve for volume, = 850/(molmass*15), figure molmass, then calculate volume.
finally, density= masssoluton/volumeL=
= 1000g/volumeL figured above
you may want to change that to g/ml

DrBob222
density x 1000 mL x %H3PO4 x (1/molar mass) = 15M
Solve for density = approximately 1.7 but you need to do it more accurately.

mass of 1000 mL = 1.73 x 1000 mL = 1730 g
mass H3PO4 = 1730 x 0.85 = 1470g
g solvent = 1730g-1470 = 260g
m = mols solute/kg solvent/kg solvent = 15/0.260 = about 57m.

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