Chemistry Problem?

Question

What is the molecular mass of a nonionic solute if 5.60 grams dissolved in 104 grams of water lower the freezing point to -0.603°C?

Answer 1

For water:

Tf = -(i)(m)(Kf)

I would break down the molality term (m) into moles solute/kg solvent. The equation above now becomes:

Tf = -(i)(moles solute/kg solvent)(Kf)

I would solve the above equation for moles solute:

moles solute = -[(Tf)(kg solvent)]/[(i)(Kf)]

= -[(-0.63)(0.104)]/[(1)(1.858)]

= 0.035 mol

Since you have the mass of the solute and you now have moles of solute, you can get its molar mass:

molar mass = mass solue / moles solute

= 5.6 g / 0.035 mol

= 160 g/mol

Answer 2

concentration of the solute 5.60/0.104 =53.84 g/L

molarity formula dt = -1.86 m

so m =0.603/1.86 =0.324mole/L

and 1 mole has a molecular weight of 53.84/0.324 =166g