Video Transcript
Which of the following statements
about solvents is correct? (A) Polar solvents dissolve polar
and nonpolar solutes, and nonpolar solvents dissolve nonpolar solutes. (B) Polar solvents dissolve polar
solutes, and nonpolar solvents dissolve nonpolar solutes. (C) Polar solvents dissolve
nonpolar solutes, and nonpolar solvents dissolve polar and nonpolar solutes. (D) Nonpolar solvents dissolve
polar solutes, and polar solvents dissolve polar and nonpolar solutes. Or (E) nonpolar solvents dissolve
polar solutes, and polar solvents dissolve polar solutes.
This question asks us to correctly
define some of the relationships between polar and nonpolar solvents and
solutes. A solute is a substance that
dissolves into another substance to form a solution. The substance which the solute
dissolves into to form the solution is known as the solvent.
One of the ways in which we can
classify solvents depends on their polarity. Polar solvents consist of polar
molecules. A polar molecule is a molecule that
contains polar bonds, which cause the molecule as a whole to have an asymmetric
distribution of electron density. These polar bonds are caused by
differences in electronegativity between the atoms in the molecule. Molecules with a symmetrical
distribution of electron density are referred to as nonpolar.
Generally speaking, it is only
possible to dissolve solutes in a solvent if the interactions between the solvent
and solute are similar to the interactions which already exist between the solute
particles themselves and the solvent particles themselves. We can summarize this idea with the
phrase “like dissolves like.”
Polar molecules, such as hydrogen
fluoride, have opposite partial charges, which allow for electrostatic interactions
to occur between molecules. In this example of hydrogen
fluoride, the intermolecular interactions are especially strong due to hydrogen
bonding, which is a special type of dipole–dipole interaction. These electrostatic interactions
are much stronger than the dispersion forces which exist between nonpolar molecules,
such as molecular hydrogen.
Due to the constant movement of
electrons, a molecule can develop a temporary dipole that induces a dipole in
another molecule if they are close enough. This results in attractive forces
between nonpolar molecules, which are instantaneous, induced dipole moments.
Polar molecules do not mix with
nonpolar substances because the interactions between polar molecules are
significantly stronger than the interactions which could be formed between polar and
nonpolar molecules. This means that mixing together the
two substances would be energetically unfavorable. And only substances of similar
polarities can dissolve in one another.
Let’s have a look at our answer
choices. We can see that answer choice (B)
applies this “like dissolves like” idea, which states that polar solvents can
dissolve polar solutes and nonpolar solvents can dissolve nonpolar solutes.
So which of the following
statements about solvents is correct? The correct answer is (B). Polar solvents dissolve polar
solutes, and nonpolar solvents dissolve nonpolar solutes.
