"Like dissolves like" is the AP Chem rule of thumb that substances with similar intermolecular interactions tend to dissolve in one another, so polar and ionic solutes dissolve in polar solvents while nonpolar solutes dissolve in nonpolar solvents (EK 3.10.A.1).
"Like dissolves like" is the shorthand version of one essential knowledge statement: substances with similar intermolecular interactions tend to be miscible or soluble in one another (EK 3.10.A.1). Polar molecules and ionic compounds dissolve well in polar solvents like water because the solute and solvent can form strong dipole-dipole interactions, hydrogen bonds, or ion-dipole attractions with each other. Nonpolar molecules dissolve well in nonpolar solvents like hexane because both rely on London dispersion forces.
Here's the intuition behind the phrase. Dissolving means breaking some solute-solute and solvent-solvent attractions and replacing them with solute-solvent attractions. That trade only works out when the new attractions are comparable to the old ones. Water molecules hydrogen-bond strongly to each other, and a nonpolar solute like I₂ can't offer water anything nearly as good, so water just keeps sticking to itself and the iodine stays undissolved. Drop that same I₂ into hexane, where everything interacts through dispersion forces anyway, and it dissolves easily. The phrase is the memory hook; the intermolecular force comparison is the actual chemistry the AP exam wants.
This term lives in Topic 3.10 (Solubility) in Unit 3 and directly supports learning objective 3.10.A: explaining the solubility of ionic and molecular compounds in aqueous and nonaqueous solvents using intermolecular interactions. It's the payoff of the whole first half of Unit 3. You learn to identify IMFs (dispersion, dipole-dipole, hydrogen bonding, ion-dipole) precisely so you can make predictions like this one. On the exam, "like dissolves like" alone is never a full answer. Credit comes from naming the specific intermolecular forces in the solute and solvent and explaining why matching forces make dissolving favorable. Think of the phrase as the conclusion of your argument, and the IMF comparison as the evidence.
Keep studying AP® Chemistry Unit 3
Intermolecular Interactions (Unit 3)
Like dissolves like is really an IMF-matching rule. Identifying whether a substance interacts through dispersion forces, dipole-dipole forces, hydrogen bonding, or ion-dipole attractions is step one of every solubility prediction.
Polarity (Unit 2)
You can't apply the rule without first deciding if a molecule is polar, and that comes from Unit 2 skills. Draw the Lewis structure, check the geometry, and see whether bond dipoles cancel. A symmetric molecule like I₂ or hexane is nonpolar even though it has bonds.
Miscible (Unit 3)
Miscibility is what the rule predicts for two liquids. Liquids with similar IMFs, like ethanol and water (both hydrogen bond), mix in any proportion; liquids with mismatched IMFs, like oil and water, separate into layers.
Homogeneous Mixture (Unit 3)
When like does dissolve like, the result is a solution, which is a homogeneous mixture with uniform composition throughout. The rule tells you which solute-solvent pairs can actually form one.
This concept shows up most often in multiple-choice questions that hand you a solute and ask you to pick a solvent, or vice versa. A classic stem describes a nonpolar organic compound that won't dissolve in water and asks what kind of solvent would work (answer: a nonpolar one, justified by matching dispersion forces). Questions also pair the rule with Lewis structures, like asking whether I₂ should dissolve in hexane based on both being nonpolar, or applying it to a lab scenario such as washing nonpolar biphenyl crystals with water versus hexane to remove ionic impurities. In free-response settings, the skill is the justification. Saying "like dissolves like" earns nothing by itself. You need to name the IMFs present in both substances and explain that similar interactions between solute and solvent particles make them soluble or miscible, which is exactly what LO 3.10.A asks for.
These get tangled because they show up in the same sentence of the CED. "Like dissolves like" is the predictive rule (similar IMFs mean substances dissolve in each other), while miscible is a description of the outcome for two liquids that mix in all proportions. Ethanol and water are miscible; the reason they're miscible is that both hydrogen bond, which is the like-dissolves-like logic. Also note that miscible is reserved for liquid-liquid mixing, while solubility covers solids and gases dissolving in solvents too.
"Like dissolves like" means substances with similar intermolecular interactions tend to be soluble or miscible in one another, which is essential knowledge 3.10.A.1.
Polar and ionic solutes dissolve in polar solvents through dipole-dipole, hydrogen bonding, or ion-dipole interactions, while nonpolar solutes dissolve in nonpolar solvents through London dispersion forces.
Dissolving is favorable when new solute-solvent attractions can replace the broken solute-solute and solvent-solvent attractions, which is why mismatched substances like oil and water stay separated.
On the AP exam, citing the phrase alone earns no credit; you have to identify the specific IMFs in both the solute and the solvent and compare them.
Determining polarity is the prerequisite step, so use Lewis structures and molecular geometry from Unit 2 before applying the rule.
It means substances with similar intermolecular interactions tend to dissolve in one another (EK 3.10.A.1). Polar solvents like water dissolve polar and ionic solutes, while nonpolar solvents like hexane dissolve nonpolar solutes such as I₂.
No. The phrase by itself is just a slogan. Full credit requires naming the intermolecular forces in both the solute and the solvent (for example, both hexane and I₂ interact only through London dispersion forces) and explaining that similar interactions make them soluble in each other.
"Like dissolves like" is the rule that predicts mixing based on similar IMFs; miscible is the label for two liquids that actually mix in all proportions. Ethanol and water are miscible because both hydrogen bond, which is the rule in action.
Water molecules hydrogen-bond strongly to each other, and nonpolar I₂ can only offer weak dispersion interactions in return. Breaking water's hydrogen bonds to make room for iodine isn't worth the trade, so water sticks to itself and the iodine stays out.
Yes. Ionic compounds dissolve in polar solvents like water because ion-dipole attractions between the ions and water molecules replace the ionic attractions in the crystal. That's why washing a nonpolar solid with water removes ionic impurities, while washing with hexane would not.
Connect this key term to the AP exam workflow: review the course, practice questions, and check related study tools.
Review units, study guides, and course resources.
Check this vocabulary in multiple-choice context.
Apply key concepts in written AP responses.
Estimate the exam score you are working toward.
Review the highest-yield facts before practice.
Put the full course together before test day.