Question

if you can use a keyboard for writing the answer I will be thankful.

Q) Consider the following compounds: methanol, ethoxyethane, ethanol, butane. Rank these compounds from least to most soluble in water. Be sure to evaluate the enthalpic changes in addition to intermolecular forces as you consider the compounds.

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Answer 1

Solubility order of the supplied compounds is :

Methanol > Ethanol > Ethoxyethane > Butane

The above order can be explained as follows :

Alcohols are much more soluble in water than are ethers and alkanes of comparable molecular weight. Their increased solubility is due to hydrogen bonding between alcohol molecules and water. As molecular weight increases, the physical properties of alcohols become more like those of hydrocarbons with comparable molecular weight. Alcohols with higher molecular weight are much less soluble in water because of the increase in size of the hydrocarbon portion of their molecules

Alcohol consists of a carbon chain (always nonpolar) and a -OH group (which is polar). For ethanol for example the chemical formula looks lie this: C2H5OH. Ethanol has a 2 carbon chain and a OH group. As water is polar it attracts OH group. Carbon chain on the other hand as nonpolar is repelled. Solubility of alcohols is therefore determined by the stronger of the two forces.

Considering these two forces the solubility order of two alcohols are CH3OH > CH3CH2OH

Butane, a nonpolar hydrocarbon, has the lowest solubility in water.

Ethoxyethane is a polar compounds, due to the presence of their polar C-O-C group, and interacts with water as a hydrogen-bond acceptor. But, they can't act as hydrogen-bond donors. As a result, ethers are less likely to be soluble in water than the alcohol with the same molecular weight.