Question

Lipids are insoluble in water because they are
A. Neutral
B. Zwitterions
C. Hydrophobic
D. Hydrophilic

Answer 1

Hint: Solubility is a property which denotes the ability of a particular solute or substance to get dissolved in the given solvent. It can be measured as the maximum amount of solute dissolved in the given solvent at equilibrium. There are many factors which can decide and affect the solubility of a given substance in the particular solvent.

Complete answer:
Let us first know about the effect of polarity of a substance on its solubility in the given solvent.
So, polarity of the substance or compound is one of the major factors affecting the solubility of that substance in the given solvent. Generally, polar solutes dissolve in polar solvents and non-polar solutes in non-polar solvents. This is referred to as “Like dissolves like”.
Let us now try to understand about the lipids and their solubility thereof in water.
So, lipids are a broad group of chemicals including fats, waxes, and steroids, etc. They are hydrophobic, meaning “water-fearing”. Some of the characteristics contributing to this attribute-
Polar and nonpolar bonds- the bonds found between carbon atoms and those between carbon and hydrogen molecules in lipids are nonpolar whereas, electrons shared in the bond between oxygen and hydrogen atoms in a water molecule are not equally shared which results in the development of slight positive charge on hydrogen and slight negative charge on oxygen atom.
Hydrogen bonding- solubility is also affected by the presence of hydrogen bonding as presence or absence of hydrogen bonding have a great cumulative effect on the physical properties of a compound.
Lipid structure- lipids have long nonpolar chains of carbon atoms which adversely affects its solubility in water.
Based on the above discussion, it is clear that lipids are insoluble in water because they are hydrophobic.

So, the correct answer is (B)- Hydrophobic.

Note:
It is noteworthy to mention that the insolubility of lipids in water molecules is largely because of the much greater affinity of water molecules for each other rather than repulsion between water molecules and lipids.
Other factors affecting solubility-
> Temperature- solubility generally increases with a rise in temperature. For gases, they become less soluble in each other and in water but become more soluble in organic solvents.
> Molecular size- if the pressure and temperature is kept constant, then out of the two particles having the same polarity, the one with smaller size will have more solubility in a given solvent.