Question

Recognize Cause and Effect Explain why alkanes, such as hexane and cyclohexane, are effective at dissolving grease, whereas water is not.

Short answer

Hexane and cyclohexane, nonpolar alkanes, effectively dissolve grease due to their nonpolar character, adhering to the "like dissolves like" principle. Grease is also nonpolar, composed of fats, oils, and long hydrocarbon chains, so it cannot dissolve in polar substances like water, which has a significant charge separation. Instead, grease is easily dissolved in nonpolar substances like alkanes.

Step-by-step solution

Discuss Polar and Nonpolar Molecules

In order to understand why alkanes such as hexane and cyclohexane can dissolve grease, and water cannot, we need to discuss the difference between polar and nonpolar molecules. Polar molecules have areas of both positive and negative charge due to an uneven distribution of electrons, while nonpolar molecules do not have significant separation of charge. This principle leads to the saying "like dissolves like", meaning that polar substances tend to dissolve other polar substances, and nonpolar substances tend to dissolve other nonpolar substances.

Define Alkanes and Their Properties

Alkanes are a class of hydrocarbons with only single bonds between carbon and hydrogen atoms. These compounds are nonpolar due to the relatively even distribution of electrons in their structures. Examples of alkanes are hexane (C6H14) and cyclohexane (C6H12), both of which have six carbon atoms and single C-H bonds.

Describe Water's Properties

Water (H2O) is a polar molecule because the oxygen atom is more electronegative than the hydrogen atoms, leading to an uneven distribution of electrons. The presence of areas with positive and negative charges makes water a good solvent for many polar substances such as salts and sugars but a poor solvent for nonpolar substances, such as grease or alkanes.

Describe Grease's Properties

Grease is composed mainly of nonpolar substances such as fats, oils, and long hydrocarbon chains. These substances do not dissolve in polar solvents such as water due to their nonpolar nature and hydrophobic interactions.

Explain the Effectiveness of Alkanes in Dissolving Grease

Since alkanes like hexane and cyclohexane are nonpolar, they effectively dissolve grease, which is also nonpolar. The nonpolar nature of alkanes allows them to easily mix with and break up the nonpolar compounds found in grease. As a result, alkanes such as hexane and cyclohexane can dissolve grease, while water, being a polar substance, cannot.

Key concepts

Polar and Nonpolar Molecules

Understanding the characteristics of polar and nonpolar molecules is fundamental to grasping why certain substances can dissolve grease while others cannot. Imagine a group of people uniformly holding a large sheet - much like molecules in a nonpolar compound, they distribute the weight evenly. In a polar molecule, however, one person might be holding more of the sheet, representing the uneven distribution of electrons. Water is an iconic polar molecule, where oxygen holds a larger 'portion of the sheet' due to its higher electronegativity compared to hydrogen atoms. Grease, on the other hand, is like a nonpolar molecule where the load (electrons) is spread evenly among the atoms.

Therefore, grease will resist blending with water, just as oil sits separate on top of a water surface. To dissolve grease, one needs a solvent with a similar lack of charge separation—like alkanes. This brings us to the principle of 'like dissolves like', a straightforward yet vital concept in chemistry. It means that substances with similar polarities tend to be soluble in one another, which helps to explain the efficiency of nonpolar solvents, such as hexane and cyclohexane, in tackling greasy substances.

Properties of Alkanes

Diving into the properties of alkanes aids in understanding their interaction with other molecules, such as grease. Alkanes are hydrocarbons consisting entirely of single bonds and are characterized by their nonpolar nature. This nonpolarity is due to the similar electronegativities of carbon and hydrogen that lead to an even distribution of electron density. Hexane and cyclohexane, for example, are part of this alkane family with simple, stable structures.

Being nonpolar gives alkanes certain advantageous properties. They are relatively inert, meaning they don't readily react with many substances. This stability, paired with their ability to dissolve other nonpolar compounds, makes them excellent for industrial applications, such as removing grease or oils in cleaning or degreasing agents. These properties of alkanes highlight their functionality beyond simple chemistry concepts, connecting us to their practical uses in everyday life.

Solubility Principles

The principles of solubility are vital for predicting which substances will dissolve in others. The key to understanding solubility lies in the interaction of molecules within a solvent and a solute. Molecules that interact similarly will likely dissolve, while a mismatch in interactions usually leads to insolubility.

For instance, the polar molecules in water are attracted to other polar molecules and ions, creating strong intermolecular bonds and leading to solubility. However, when faced with a nonpolar substance, these attractions do not form, resulting in poor solubility. The greasy or oily substances are mostly nonpolar, meaning they are more soluble in nonpolar solvents like alkanes. This principle explains why washing greasy hands with just water won't clean them effectively, but adding soap, which contains parts that can interact with both polar water and nonpolar grease, does the job. By applying these solubility principles, one can deduce many everyday phenomena, from cleaning processes to the extraction of certain chemicals in laboratories.