Mole fraction to percent by mass. Convert 0.1538 mole fraction of propanol (C 3

Question

Mole fraction to percent by mass. Convert 0.1538 mole fraction of propanol (C3H8O) in water to percent by mass of propanol in the solution. (Some of the calculations from the previous question can speed up the process here.) Answer to 4 significant figures with appropriate units.

Parts per million to molarity. The daily intake of iron is 18 mg for an adult. This dose dissolved as Fe2+ ions in 1 liter of water makes an 18 ppm Fe2+solution. Convert 18 ppm Fe2+ to molarity. Assume the aqueous solution is dilute enough to use the shortcut and the solution density is essentially

equal to water (1.0 g/mL). Answer to 2 significant figures with appropriate units.

Molality to percent by mass. Convert the molality of a 2.35 mol/kg RbNO3(aq) solution to percent by mass. (Hint: begin by separating the 2.35 mol RbNO3 and the 1 kg water.) Answer to 3 significant figures with appropriate units.

Explanation / Answer

propanol mole fraction = 0.1538 /1

this means = 0.1538 moles

water moles = 1 - 0.1538 = 0.8462

mass of propanol = moles x molar mass = 0.1538 x 60 = 9.23 g

mass of water = 0.8462 x 18 = 15.23

mass % of propanol = (9.23 / 9.23 + 15.23 ) x 100

                             = 37.73 %

Parts per million to molarity.:

18 ppm = 18 mg /L = 18 x 10^-3 g / L

               = (18 x 10^-3 / 55.85) mol /L

               = 3.2 x 10^-4 M

molarity = 3.2 x 10^-4 M

Molality to percent by mass:

moles of solute = 2.35

mass of solute = moles x molar mass = 2.35 x 147.5 = 346.6 g

mass of solvent = 1 kg = 1000 g

mass % = (346.6 / 346.6 + 1000) x 100

                = 25.7 %

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