Chapter 17: Problem 119

Which do you expect to be most water-soluble: (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) Explain your answer.

Short Answer

Expert verified

The most water-soluble molecule is ethanol (\(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\)) because it has a polar hydroxyl group and a small nonpolar carbon chain, enabling it to interact with water molecules more easily than propane or hexanol.

Step by step solution

Identify the molecules

First, we need to identify the given molecules: (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) is ethanol (a 2-carbon alcohol) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\) is propane (a 3-carbon alkane) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) is hexanol (a 6-carbon alcohol)

Determine the polarity of each molecule

Now, let's determine the polarity of each molecule. (a) Ethanol: Ethanol has a polar hydroxyl group (\(\mathrm{OH}\)) due to the high electronegativity of oxygen atoms. This means that ethanol has a polar region and can interact with the polar water molecules. (b) Propane: Propane is an alkane made up of only nonpolar carbon-hydrogen bonds. It does not have any polar regions, which means it cannot interact with polar water molecules. (c) Hexanol: Hexanol has a polar hydroxyl group (\(\mathrm{OH}\)) due to the high electronegativity of oxygen atoms. This means that hexanol, like ethanol, has a polar region and can interact with the polar water molecules.

Compare the solubilities of the molecules

Considering the polarities of the molecules, we can now compare their solubilities in water. (a) Ethanol has a polar hydroxyl group and a small nonpolar carbon chain, which means it can interact with water molecules and dissolve easily. (b) Propane is entirely nonpolar and has no polar regions to interact with water. It will not dissolve well in water. (c) Hexanol has a polar hydroxyl group, but also a long nonpolar carbon chain. Although the polar group can interact with water, the long nonpolar chain makes it difficult to dissolve in water, making it less soluble than ethanol.

Determine the most water-soluble molecule

Among the three molecules, ethanol (\(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\)) is expected to be the most water-soluble due to its polar hydroxyl group and small nonpolar carbon chain, which allows it to interact with water molecules more easily than propane or hexanol.

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Which do you expect to be most water-soluble: (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) Explain your answer.

Short Answer

Step by step solution

Identify the molecules

Determine the polarity of each molecule

Compare the solubilities of the molecules

Determine the most water-soluble molecule

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