Question

Determine the molality of an aqueous solution of glucose whose mole fraction of glucose is 0.035. Glucose is a non-electrolyte (hint: one does not need the formula for glucose).

I have the correct answer (2.02 m) however I am having issues figuring out how the answer was found (my answers when I try to attempt to solve the problem are way off). Can anyone please help me with the process? If possible, please show work/formulas

Answer 1

now

we know that

mole fraction = moles / total moles

also

total moles = moles of glucose + moles of water

so

mole fraction = moles of glucose / ( moles of glucose + water)

0.035 = moles of glucose / ( moles of glucose + water)

solving we get

moles of glucose = 0.03627 moles of water

now

we know that

molality = moles of glucose / mass of water

but

mass of water = moles x molar mass

so

mass of water = 18 x moles of water

now

molality = moles of glucose / 18 x moles of water

molality = 0.03627 moles of water / 18 x moles of water

molality = 2.015 x 10-3

so

the molality is 2.05 x 10-3