Question

Which compound is the most soluble in water?
A. Chloroethane
B. Ethanol
C. Ethanal
D. Ethylene glycol

Answer 1

Hint: We have to find the one which is most soluble in water. Therefore, we must understand which compounds have the highest number of hydrogen bonds with water. Then only we can understand the solubility of compounds.

Complete step to step solution:
Let’s start with the basic concept of hydrogen bonding; hydrogen bond is a dipole-dipole attraction between two molecules. It is not a covalent bond with hydrogen. It mainly happens between hydrogen and highly electronegative atoms such as nitrogen (N), oxygen (O) and fluorine (F).
The electronegativity goes like\[F{\text{ }} > {\text{ }}O{\text{ }} > {\text{ }}N \approx Cl\], with fluorine be most electronegative followed by oxygen then nitrogen and chlorine.
Hydrogen bonding can be intermolecular (between two different molecules) and intramolecular (in the same molecule itself) both, the example of intramolecular are ortho nitrophenol and boric acid.
Higher the number of hydrogen bonds formed between water and another covalent molecule, more the molecule soluble in water.
Now, we have a basic understanding of hydrogen bonding. Let’s write the molecular formula of these four
\[Chloroethane:{\text{ }}Cl{H_2}C{\text{ }} - {\text{ }}C{H_3}\]
\[Ethanol:{\text{ }}C{H_3}-{\text{ }}CH2{\text{ }}-{\text{ }}OH\]
\[Ethanal:{\text{ }}C{H_3}-{\text{ }}CHO\]
\[Ethylene{\text{ }}glycol:{\text{ }}OH{\text{ }}-{\text{ }}C{H_2}-{\text{ }}C{H_2}-{\text{ }}OH\]
The maximum no. of hydroxyl group in ethylene glycol is 2. Since 2 hydroxyl groups are present in ethylene glycol, it will form the maximum no. of hydrogen bonds with the water molecules and hence, will be more soluble as compared with others.

So, we can conclude that the answer to this question is D. Ethylene glycol.

Note: We must understand that the organic compounds tend to dissolve well in solvents that have similar properties to themselves. This chemical nature is often referred to as "like dissolves like," which means that polar molecules will generally dissolve well in polar solvents and nonpolar molecules will generally dissolve in non-polar solvents.