Question

Part 1 - Miscibility Tests A. Hexanes and water are: Miscible Immiscible B. Knowledge of structure explains IMFs, which can be used to explain miscibility, Table 1: Complete the table below. In the boxes for the VSEPR diagrams (see Figure 3 as a guideline): • identify the most polar bond(s) by placing 8+ and 8-charges on their atoms • list bond dipoles VSEPR Structures include any molecular dipole) IMF() Present in pure sample Bond Dipole(s) Water Hexanes C. Which IMF(s) exist(s) between hexanes and water? D. Use your answer for C to explain A.

Answer 1

a) Hexanes and water are immiscible.

b) The water molecule has only one type of bond:

H5* H io

And in the pure sample there are mainly dipole-dipole interactions and hydrogen bonding. The bond dipole value is 1.5 D (the total dipole moment of the molecule is 1.84 D).

We will take hexane as a reference for the mixture that is hexanes. The most polar bond is the C-H bond, which is very lowly polar in absolute terms:

Н нн Н .Н бс Н. с с Нo Н б+ Н Н н нн Н エー I

The C-H bond dipole moment is around 0.41 D and the C-C bond dipole is 0 (the total dipole moment of the molecule os 0.09 D) and the main IMFs that will occur in a pure sample are dispersion forces: induced dipole-induced dipole.

C and D) Between hexanes and water, the IMF forces in play are dipole-induced dipole forces, which are quite weak, which explains why water molecules prefer to interact only with water molecules and hexanes molecules prefer to interact solely with their own kind, hence the immiscibility of the liquids.