Question

Why are alkanes insoluble in water but soluble in organic solvents?
A) they have high density
B) they have weak bonds
C) they cannot break the bonds in water
D) all of above

Answer 1

Hint: The alkanes are the hydrocarbons which are saturated as they contain single bonds only. The general formula of alkane is ${C_n}{H_{2n + 2}}$. The alkanes will be soluble in the solvents that form new bonds or interaction with them, these newly formed interactions should be strong enough to break the previous bonds.

Complete answer:
The only new interactive force between alkanes and water molecules is the Van der Waals force. Alkanes do not dissolve in water because these forces do not release enough energy to supplement the energy required to break the hydrogen bonds in water.
Water molecules have intermolecular hydrogen bonding and make it polar solvent. In case of organic solvents, no such bonds are present, thus solubility of alkane in organic solvents is higher.
Thus, the alkanes are insoluble in water but soluble in organic solvents because they cannot break the bonds in water.

Hence, the correct option is C) they cannot break the bonds in water.

Note:
Water is very polar. Alkanes are not polar. The polarity of the organic solvent is very low. Therefore, alkanes are more compatible with organic solvents. The electric field at the molecular level is everything. The simple concept here is that like dissolves like which means polar dissolves polar and nonpolar dissolves nonpolar.