Why is water sometimes called the “universal solvent”?
A.
Because water dissolves all solutes equally well.
B.
Because water is a nonpolar solvent.
C.
Because water is good at dissolving ions and polar molecules.
D.
Because water is poor at dissolving nonpolar molecules.
The Correct Answer and Explanation is:
The correct answer is C. Because water is good at dissolving ions and polar molecules.
Explanation:
Water is often referred to as the “universal solvent” due to its remarkable ability to dissolve a wide range of substances, especially ionic compounds and polar molecules. This unique property stems from its molecular structure and the resulting interactions it can form with other substances.
Water (H₂O) is a polar molecule, meaning it has a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. This polarity arises because of the significant difference in electronegativity between hydrogen and oxygen. The oxygen atom pulls the shared electrons in the O-H bonds closer to itself, creating a dipole moment. This dipole moment endows water with its ability to interact with various solutes.
When water encounters an ionic compound, such as sodium chloride (NaCl), the positive end of the water molecules is attracted to the negative chloride ions, while the negative end of the water molecules is attracted to the positive sodium ions. This interaction disrupts the ionic bonds holding the NaCl together and surrounds the individual ions, effectively dissolving the compound.
Similarly, water is effective at dissolving polar molecules due to its own polarity. Polar molecules, such as sugar (sucrose), have regions of partial positive and partial negative charges. Water molecules interact with these regions, breaking the intermolecular forces between the sugar molecules and surrounding them, allowing the sugar to dissolve.
However, water is less effective at dissolving nonpolar substances, such as oils or fats. Nonpolar molecules do not have charges or dipole moments and thus do not interact well with the polar water molecules. This mismatch is why nonpolar substances often remain separate from water.
In summary, water’s designation as the “universal solvent” is due to its ability to dissolve a vast range of substances, particularly those that are ionic or polar, through its polar nature and the hydrogen bonding interactions it can form.