Question

What intermolecular forces are present when glycerin, water, canola oil, and dish soap are mixed?

Lab procedure:

1. Glycerin and water are added to a test tube. There are now two layers: glycerin on bottom and water on top.
2. Canola oil is added to the tube and stirred; there is now a water/glycerin layer on bottom, and canola oil layer on top.
3. Dish soap is added to the tube and stirred; all parts are now mixed, then separate once allowed to settle.

What intermolecular forces are present in each step that causes the layers to combine / separate?

Answer 1

1. Glycerine and water both have hydrogen bonds in their structure. Water has one OH group and glycerine have three OH group in their molecular structure. Due to more inter molecular H-bond glycerine is more viscous so it is heavy and will be at the bottom when mixed with water.

2. Canola oil is a vegetable oil but having lower density than water. Water has 1 gm/cc density and in respect to that the oil has 0.92 gm/cc so it will be on the top of layer. In terms of inter molecular forces canola oil has induced dipole forces which is non polar type and different from polar H bonding forces. So as the forces in water is polar and canola oil is non polar so they will be having different interfacial tension and be immiscible.

3. When dish soap is added to the tube the infterfacial tension of all the liquids decreases. Soap is surfactant which works by reducing interfacial tension of different layer of liquids, they also increases the contact angle of molecule from different intermolecular forces and help them to be miscible.