Question

which one of the following is most soluble in water? a) ch₃oh b) ch₃ch₂oh c) ch₃ch₂ch₂oh d) ch₃ch₂ch₂ch₂oh

Explanation:

To determine solubility in water, we consider the "like dissolves like" principle and the balance between the hydrophilic (-OH group, which can form hydrogen bonds with water) and hydrophobic (hydrocarbon chain) parts of the alcohol molecules. As the length of the non - polar hydrocarbon chain (the part with $CH_2$ and $CH_3$ groups) increases, the hydrophobic nature of the alcohol increases, while the hydrophilic nature (due to the -OH group) remains relatively constant in terms of its ability to form H - bonds with water.

• For option a: $CH_3OH$ (methanol) has a very short hydrocarbon chain (only one carbon atom in the chain, $CH_3 -$). The -OH group can form strong hydrogen bonds with water molecules, and the small size of the hydrocarbon part means that the hydrophobic effect is minimal.
• For option b: $CH_3CH_2OH$ (ethanol) has a longer hydrocarbon chain (two carbon atoms, $CH_3CH_2 -$) compared to methanol. So, the hydrophobic part is larger, and its solubility in water will be less than that of methanol.
• For option c: $CH_3CH_2CH_2OH$ (propanol) has a three - carbon hydrocarbon chain. The hydrophobic portion is even larger, reducing its solubility in water further compared to methanol and ethanol.
• For option d: $CH_3CH_2CH_2CH_2OH$ (butanol) has a four - carbon hydrocarbon chain. The hydrophobic effect is the most pronounced among these four alcohols, making it the least soluble in water.

Since methanol has the shortest non - polar hydrocarbon chain, it has the highest solubility in water among the given alcohols.

Answer:

a) $CH_3OH$