Question

Calculate the molality of a 5.86 M ethanol solution whose density is 0.927? ( molar mass of ethanol=46.07

Answer 1

Answer:

The concentration of a substance can be expressed in several quantities such as moles, percent (%) weight / volume,), molarity, molality, parts per million (ppm) or mole fraction. The concentration shows the amount of solute in a unit of the amount of solvent.

Molality shows the number of moles dissolved in every 1000 grams of solvent.

\rm m=\dfrac{n\times 1000}{p}m=

p

n×1000

m = Molality

n = Number of moles of solute

p = Solvent mass (grams)

\rm m=\dfrac{mol\:solute}{mass\:solvent(kg)}m=

masssolvent(kg)

molsolute

Given

Molarity of ethanol (C₂H₅OH) = 5.86 M

Density = 0.927 g / ml = 0.927 kg / L

Asked

molality

Solution

Because molality is the number of moles of solute per mass of solvent (in Kg), we determine the number of moles of solute and mass of solvent

We make the assumption of 1 L of solution, then

1. mole of solute ethanol (C₂H₅OH)

5.86 M = 5.86 moles per 1 L solution so that moles of ethanol (C₂H₅OH) = 5.86

2. mass of solvent (water)

the mass of the solution is:

m solution = density x volume

m solution = 0.927 kg / L x 1 L

m solution = 0.927 kg

mass of ethanol (C₂H₅OH) = mole x molar mass of ethanol

ethanol mass = 5.86 x 46.07 g / mol

ethanol mass = 269.97 g = 0.26997 kg

then the solvent mass (water)

mass of solvent = mass of solution - mass of ethanol

solvent mass = 0.927 - 0.26997

solvent mass = 0.65703 kg

So the molality (m)

\begin{gathered}\rm m=\dfrac{mole\:ethanol}{solvent\:mass}\\\\m=\dfrac{5.86}{0.65703}\\\\m=\boxed{\bold{8.919\approx8.92}}\end{gathered}

m=

solventmass

moleethanol

m=

0.65703

5.86

m=

8.919≈8.92