State the kind of intermolecular forces that would occur between the solute and solvent in each.
A) isopropyl alcohol (polar, contains an OH group)
B) sodium chloride (ionic)
C) vegetable oil (nonpolar)
D) sodium nitrate (ionic)
The correct answer and explanation is :
To understand the intermolecular forces between solute and solvent, we need to look at the properties of the solute and solvent in each case. The intermolecular forces that come into play depend on the polarity, charge, and other characteristics of the substances involved.
A) Isopropyl Alcohol (polar, contains an OH group)
Isopropyl alcohol is a polar molecule because of its hydroxyl group (-OH), which allows hydrogen bonding with other molecules. When it is dissolved in a solvent, the primary intermolecular forces that would occur are:
- Hydrogen bonding: The OH group can form hydrogen bonds with other polar molecules or solvents that contain hydrogen atoms bonded to electronegative atoms like oxygen or nitrogen.
- Dipole-dipole interactions: The partial positive charge on the hydrogen atoms and the partial negative charge on the oxygen atom can interact with the dipoles of other polar molecules.
- Van der Waals (dispersion) forces: These forces are weaker but still present due to the movement of electrons in nonpolar parts of the molecule.
If isopropyl alcohol is dissolved in water (a polar solvent), hydrogen bonds between the OH group of isopropyl alcohol and water molecules would dominate.
B) Sodium Chloride (Ionic)
Sodium chloride (NaCl) is an ionic compound, and when it dissolves in water, it dissociates into sodium (Na⁺) and chloride (Cl⁻) ions. The intermolecular forces in this case are:
- Ion-dipole interactions: The ions (Na⁺ and Cl⁻) interact with the polar solvent molecules, such as water. The positive sodium ions will be attracted to the partial negative charges on the oxygen atom of water, while the negative chloride ions will be attracted to the partial positive charges on the hydrogen atoms of water.
- Ion-ion interactions: In the solid NaCl, ions interact strongly with each other through electrostatic attraction. However, when dissolved, the ion-ion interactions are replaced by ion-dipole interactions with the solvent.
In the case of NaCl dissolved in water, ion-dipole interactions are the primary forces at play.
C) Vegetable Oil (Nonpolar)
Vegetable oil is primarily composed of long hydrocarbon chains, making it a nonpolar substance. When it is dissolved in a solvent, the intermolecular forces would include:
- London dispersion forces (van der Waals forces): Since vegetable oil is nonpolar, the primary intermolecular force between the molecules is the weak London dispersion force, which arises from temporary dipoles created by electron movement in the molecules.
- Dipole-induced dipole forces: If vegetable oil interacts with a polar solvent, the nonpolar oil molecules may induce a temporary dipole in the polar solvent molecules. However, these forces are relatively weak.
If vegetable oil is mixed with a nonpolar solvent like hexane, London dispersion forces would dominate.
D) Sodium Nitrate (Ionic)
Sodium nitrate (NaNO₃) is also an ionic compound, and it dissolves in water to dissociate into Na⁺ and NO₃⁻ ions. The intermolecular forces that occur are:
- Ion-dipole interactions: Similar to sodium chloride, sodium nitrate will interact with polar water molecules through ion-dipole interactions. The sodium ions will interact with the negative dipole of water, while the nitrate ions will interact with the positive dipoles of water molecules.
- Ion-ion interactions: In the solid form, sodium and nitrate ions experience strong ion-ion interactions, but these are overcome when the compound dissolves in water.
Thus, the primary force in the case of NaNO₃ dissolved in water would be ion-dipole interactions.
Conclusion
The intermolecular forces in each scenario depend largely on the polarity and ionic nature of the solute and solvent. Polar solutes like isopropyl alcohol form hydrogen bonds and dipole-dipole interactions, while ionic compounds like sodium chloride and sodium nitrate primarily exhibit ion-dipole interactions when dissolved in polar solvents. Nonpolar solutes like vegetable oil interact via London dispersion forces with their solvent. These interactions determine the solubility and behavior of substances in different solvents.