Find the morality and molality

Question

16.0 g CH3OH and 50.0 g water are combined to make a solution. What is the molarity and molality of methanol (CH3OH) in the solution if the density of the solution is 0.955 g/mL?

Answer 1

first let calculate the number of moles of methanol 16 g / 32 g / mole = 0.5 moles.

Molality is defined as the number of moles of a solute dissolved in 1000 g solvent.

As there are 0.5 moles methanol and 50 g water (solvent), the molality is 0.5 mole CH3OH /50g x 1000g H2O = 10 molal.

For molarity, calculate the number of mL of the solution: 1mL / 0.955 g x (16 + 50.0)g =69.1 mL of solution. As there are 0.5 moles in 69.1 mL, there are 0.5moles CH3OH / 69.1mL x 1000 mL/liter = 7.24 molar.

I used whole numbers for the molecular mass of methanol; you may want to calculate using more exact figures. Please check math.

FYI: it's molarity not morality.