Question

which of the following aqueous solutions has the largest molality of benzoic acid (c6h5cooh)

Answer 1

a) molallity = 4.5

b)

consider 100 g of water

moles = 100 / 18 = 5.556

molfraction of benzoic acid = moles of benzoic acid / ( moles of benzoic acid + water)

so

0.05 = y / (y + 5.556)

y = 0.29

so

molality = 0.29 x 1000 / 100

molality = 2.9

c) consider

1000 g of solution

mass of benzoic acid = 25 g

moles = 25 / 122 = 0.205

now

mass of water = 1000-25 = 975

so

molality = 0.205 x 1000 / 975

molality = 0.21

d)

moles = mass / molar mass

so

moles of benzoic acid = 3.2 / 122 = 0.02623

now

molality = 0.02623 x 1000 / 650

molality = 0.04

e)

mass = moles x molar mass

so

mass of water = 65 x 18 = 1170

now

molality = 1.5 x 1000 / 1170

molality = 1.282

so

answer is a) 4.5m C6H5COOH