Chapter 13: Problem 10
Explain why ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) is not soluble in cyclohexane \(\left(\mathrm{C}_{6} \mathrm{H}_{12}\right)\)
Short Answer
Expert verified
Ethanol is polar, cyclohexane is nonpolar; like dissolves like, thus ethanol doesn't dissolve in cyclohexane.
Step by step solution
01
Understand Solubility
Solubility is the ability of a substance (the solute) to dissolve in a solvent. It depends on the interactions between the molecules of the solute and the solvent. A general rule of thumb is 'like dissolves like,' meaning polar solvents dissolve polar solutes and nonpolar solvents dissolve nonpolar solutes.
02
Identify the Polarity of Ethanol
Ethanol \((\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH})\) is a polar molecule. It has a hydroxyl group \((\mathrm{-OH})\), which is highly polar due to the electronegativity difference between oxygen and hydrogen, creating a dipole moment.
03
Identify the Polarity of Cyclohexane
Cyclohexane \((\mathrm{C}_{6} \mathrm{H}_{12})\) is a nonpolar molecule. It is composed entirely of carbon-carbon and carbon-hydrogen bonds, which share electrons more equally, resulting in a lack of polarity.
04
Analyze Solvent-Solute Interaction
Since 'like dissolves like,' polar ethanol will dissolve best in polar solvents. Cyclohexane, being nonpolar, cannot effectively interact with the polar ethanol molecules. The nonpolar cyclohexane lacks the ability to disrupt the hydrogen bonding within ethanol, making the interaction unfavorable.
05
Conclusion on Solubility
Ethanol is not soluble in cyclohexane because the polar ethanol molecules cannot form sufficient interactions with the nonpolar cyclohexane molecules to dissolve, adhering to the 'like dissolves like' principle.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polarity of Molecules
Molecules are either polar or nonpolar depending on their structure and the distribution of their electrical charge. Polarity arises from differences in electronegativity between atoms bonded together. When atoms have different electronegativities, electrons are not shared equally, causing a dipole or a separation of charge across the molecule.
For instance, ethanol (\( \text{C}_{2} \text{H}_{5} \text{OH} \)) contains a highly polar hydroxyl group (\( \text{-OH} \)). The oxygen atom in the hydroxyl group is more electronegative than hydrogen, pulling more electrons towards itself and creating a positive and negative end on the molecule. Ethanol, therefore, exhibits a strong dipole moment.
On the other hand, cyclohexane (\( \text{C}_{6} \text{H}_{12} \)) is nonpolar because it is composed of carbon-carbon and carbon-hydrogen bonds, which are relatively nonpolar. The electrons in these bonds are shared more equally, resulting in no significant dipole moment or separation of charge. The nonpolar nature of cyclohexane makes it incompatible for interaction with polar substances like ethanol.
For instance, ethanol (\( \text{C}_{2} \text{H}_{5} \text{OH} \)) contains a highly polar hydroxyl group (\( \text{-OH} \)). The oxygen atom in the hydroxyl group is more electronegative than hydrogen, pulling more electrons towards itself and creating a positive and negative end on the molecule. Ethanol, therefore, exhibits a strong dipole moment.
On the other hand, cyclohexane (\( \text{C}_{6} \text{H}_{12} \)) is nonpolar because it is composed of carbon-carbon and carbon-hydrogen bonds, which are relatively nonpolar. The electrons in these bonds are shared more equally, resulting in no significant dipole moment or separation of charge. The nonpolar nature of cyclohexane makes it incompatible for interaction with polar substances like ethanol.
Hydrogen Bonding
Hydrogen bonding is a special type of attraction between molecules, more significant than typical dipole-dipole interactions. It occurs when a hydrogen atom bonded to a strongly electronegative atom like oxygen, nitrogen, or fluorine, becomes slightly positive. This positive hydrogen is then attracted to the electronegative atom in a nearby molecule.
In ethanol, hydrogen bonding prominently occurs due to its hydroxyl group (\( \text{-OH} \)). The hydrogen in this group can form strong bonds with the oxygen of other ethanol molecules. This strong hydrogen bonding is crucial as it stabilizes ethanol's molecular interactions in solutions with other polar substances.
However, cyclohexane lacks this ability to form hydrogen bonds because it does not have atoms with significant partial charges. Consequently, it cannot effectively interact with ethanol through hydrogen bonding, leading to ethanol's poor solubility in cyclohexane.
In ethanol, hydrogen bonding prominently occurs due to its hydroxyl group (\( \text{-OH} \)). The hydrogen in this group can form strong bonds with the oxygen of other ethanol molecules. This strong hydrogen bonding is crucial as it stabilizes ethanol's molecular interactions in solutions with other polar substances.
However, cyclohexane lacks this ability to form hydrogen bonds because it does not have atoms with significant partial charges. Consequently, it cannot effectively interact with ethanol through hydrogen bonding, leading to ethanol's poor solubility in cyclohexane.
Solvent-Solute Interaction
Solubility fundamentally depends on the interactions between the molecules of the solute and the solvent. Polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes; this is the 'like dissolves like' principle. It's all about how well the solvent can stabilize the solute molecules by surrounding and interacting with them.
Ethanol, being polar, is more likely to dissolve in a polar solvent because it can engage in hydrogen bonding and strong dipole interactions with other polar molecules. This facilitates ethanol's uniform distribution in the solvent.
Cyclohexane, in contrast, is a nonpolar solvent, incapable of forming hydrogen bonds or any strong attractions with polar molecules like ethanol. The lack of interaction means that ethanol will not get enveloped by cyclohexane's molecules, leading to poor solubility. Therefore, despite its solvent qualities, cyclohexane is not suitable for dissolving polar ethanol due to the absence of significant solvent-solute interactions.
Ethanol, being polar, is more likely to dissolve in a polar solvent because it can engage in hydrogen bonding and strong dipole interactions with other polar molecules. This facilitates ethanol's uniform distribution in the solvent.
Cyclohexane, in contrast, is a nonpolar solvent, incapable of forming hydrogen bonds or any strong attractions with polar molecules like ethanol. The lack of interaction means that ethanol will not get enveloped by cyclohexane's molecules, leading to poor solubility. Therefore, despite its solvent qualities, cyclohexane is not suitable for dissolving polar ethanol due to the absence of significant solvent-solute interactions.