Question

Why partial molar volume is important for life?

What we can learn from it (NaCl and KCl salts)

Answer 1

Partial molar volumes tells about the interaction between the different components of the mixture and about the local structure of the solvent. In particular we can say (water effects in the partial molar volume may be seen due to breaking of local water structure or even creating ice like structures ("iceberg model") around hydrophobic solutes). There is a theory called Kirkwood-Buff theory in which the partial molar volumes (together with other thermodynamic parameters) can be related to integrals over the pair correlation functions between solvent and solute molecules. In the past people tried to use these theories also to understand thermodynamic properties of solutions of amino acids and small peptides.

Partial molar volumes help to assess the influence of pressure on phase equilibria or reaction equilibria. The prediction of partial molar volumes or excess volumes is a sharp test for theories of the fluid state. The partial molar volume is broadly understood as the contribution that a component of a mixture makes to the overall volume of the solution.

Basically it tells us about the interaction between the different components of the mixture (for example in KCL (K+ and Cl-)) and tellsus about the basic structure of the solvent.

Imagine adding 1 mole (18 g) of H2O(l) to a very large volume of water.The volume would increase by 18 cm3, and we would say that dV/dn=18cm³/mol and would call this the Partial Molar Volume of water.

example At 20 ^oC, the density of a 20% by mass solution of Ethanol and Water is0.97 g/cm³? Given that the Partial Molar Volume of ethanol in this solution is52.2 cm³/mol, what is the Partial Molar Volume of water?

M(EtOH) = 46 g/mol M(H₂O) = 18 g/mol

Let us Assume 1000 cm³ of solution.

m(EtOH) = 194 g -------n(EtOH) = 4.22 mol

m(H₂O) = 776 g --------- n(H₂O) = 43.1 mol

V(H₂O) = 18.1 cm³/mol