Question

We have a solution of H₂O (0.1 wt%) and H₂SO₄ (0.9 wt%).

Find the mass density (Ib_m/ft³) and molar concentration (Ib-mole/ft³) of water in this mixture?

Answer 1

The solution contains H₂O (0.1 wt%) which means 100ml of solution has 0.1 g of water. This is the standard definition. So 1000 ml or 1 litre solution have 1g water. The molecular weight of water is 18g/mol. So 1 litre of the solution contains 1/18 = 0.056 mol of water. So the concentration of water is 0.056 M. This is in SI unit.

Now 100 ml means 0.00353 ft³ and 1 gm means 0.00220462 lbm. So we can say 0.00353 ft³ solution contains 0.1 g= 0.000220462 lb water. So 1 ft³ solution contains (.000220462/ 0.00353) lb =0.062 lb water. (approximated to 3rd decimal). So mass density of water is 0.062 lbm/ft³ . Now 1 pound mol or lb-mol has 18 lb-mass water. So the molar concentration in of the given solution in Ib-mole/ft³ = 0.062/18 = 0.0034 Ib-mole/ft³