Intermolecular forces explain the characteristics of certain compounds, However,

Question

Intermolecular forces explain the characteristics of certain compounds, However, it also explains why certain compounds will mix together or not mix together. Why do oil and water not mix? Why may detergents and soaps force them to mix? What are some examples of similar mixtures you might encounter in your life? ((You have to understand the concept of polarity to understand this question on a molecular basis. Then, you have to know the structure of water, oil (which is a hydrocarbon - Chapter 3 - Organic section), and detergent.

Explanation / Answer

Why do oil and water not mix?

When oil and water are put together in the same container, the oil immediately separates itself from the water and floats in the surface of the water, forming a glob or bead. Even vigorous stirring or shaking cannot mix them. The reason for this is that water and oil have different structure. Water is polar molecule its hydrogen component overwhelms the oxygen that charges its ion. On the other hand, oil is non-polar it is not charged. It consists of many C-H bonds that make it hydrophobic or water-fearing. Base on the scientific principle that like dissolves like, which means polar molecule dissolves polar molecule and non-polar dissolves non-polar, water cannot dissolve oil, or vice versa. There is no interaction between the two compounds because the molecule of water cannot form a bond with the molecules of the oil therefore, they do not mix.

Why may detergents and soaps force them to mix?

Although water and oil differ in their ionic charge, they can be mixed with the addition of soap. Soap, commonly used in cleaning away dirt and grease that cannot be removed by plain water, has two unlike ends. Its one end is polar or hydrophilic, which is water-loving and dissolves in water on the other end is non-polar or hydrophobic, which avoids water but can dissolve non-polar molecules. When soap is added in oil with water, the polar end of the soaps molecule interacts and forms a bond with water molecule. This interaction creates an aggregation or clustering of   molecules called micelle. A micelle is a cluster of many soap molecules that bond together in a spherical shape wherein the hydrophilic heads are exposed outside while their non-polar tails, which do not interact with water, are inside. Since these tails attract non-polar molecules, the oil molecules are enclosed and dissolved inside the micelle. When water dissolves the soap, the oil within the micelle mixes with the water.

Understanding of Polarity

Polarity is when one end is positively charged while the other end is negatively charged. Each water molecule is made of two hydrogen atoms and one oxygen atom. But the atoms are not arranged in a line. The two hydrogen atoms cling to one side of the oxygen atom making the molecule look something like a Mickey Mouse head. The electrons in the molecule spend more time on the oxygen side of the molecule, giving this side a negative charge and the hydrogen side a positive charge. Only other polar molecules can dissolve in water because polar molecules dissolve only in polar solvents and non-polar molecules dissolve only in non-polar solvents.

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