Question

Calculate the molality, molarity,and mole fraction of NH₃ in an 14.60 mass % aqueous solution (d = 0.9651g/mL)

Answer 1

consider 100 g of the solution

given

mass % = 14.60

we know that

mass percent = ( mass of solute / mass of solution ) x 100

so

14.60 = ( mass of NH3 / 100 ) x 100

mass of NH3 = 14.60

mass of water = 100-14.60

mass of water = 85.4

now

moles = mass / molar mass

so

moles of water = 85.4 / 18

moles of water = 4.7444

moles of NH3 = 14.60 / 17

moles of NH3 = 0.8588

so

total moles = 4.7444 + 0.8588

total moles = 5.6032

now

we know that

mole fraction = moles of Nh3 / total moles

so

mole fraction of NH3 = 0.8588/5.6032

mole fraction of NH3 = 0.153

now

molality = moles of Nh3 / mass of solvent (kg)

so

molality = 0.8588 / 85.4 x 10-3

molality = 10

so

the molality is 10 m

now

volume of solution = mass of solution / density

volume of the solution = 100 / 0.9651

volume of solution = 103.616 ml

now

molarity = moles of NH3 / volume of solution (L)

so

molarity = 0.8588 / 103.616 x 10-3

molarity = 8.3

so

the molarity is 8.3 M