In this post, I want to share how to estimate density of liquid mixture. This calculation is very simple yet useful for process engineers.
Density of liquid mixture can be estimated from density of pure components in the mixture. Many handbooks have a large database of density of pure liquids. Density of most organic liquids usually lies between 800 and 1000 kg/m3, except than those containing a halogen or other “heavy atom”.
Density at normal boiling point can be obtained from the molar volume.
ρb = density, kg/m3
M = molecular mass
Vm = molar volume, m3/kmol
For mixtures, it is usually sufficient to take the specific volume of the components as additive, even for non-ideal solution.
Let’s see example below.
Calculate the density of a mixture and water at 20oC, composition 35% w/w methanol.
Density of water at 20oC is 998.2 kg/m3
Density of methanol at 20oC is 791.2 kg/m3
Because the concentration of methanol is expressed in weight percent, then we need to define the basis in weight also.
Basis = 100 kg
Volume of water = (100% – 35%) × 100 / 998.2 = 0.065 m3
Volume of methanol = 35% × 100/ 791.2 = 0.044 m3
Total volume = 0.065 + 0.044 = 0.109 m3
Density of mixture = mass of mixture / volume of mixture = 100 / 0.109 = 917.43 kg/m3
I hope you find this simple post is useful.