--- title: "Why Some Things Dissolve and Others Do Not" description: "Dissolving separates solute particles and brings them into contact with a solvent. Attractions and the tendency of particles to mix affect solubility. Polarity helps explain why salt and sugar dissolv" canonical: https://lightmysky.com/learn/science/why-some-things-dissolve-and-others-do-not-mt__njIrlqqqL source: https://lightmysky.com/learn/science/why-some-things-dissolve-and-others-do-not-mt__njIrlqqqL.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Why Some Things Dissolve and Others Do Not Dissolving separates solute particles and brings them into contact with a solvent. Attractions and the tendency of particles to mix affect solubility. Polarity helps explain why salt and sugar dissolve in water while oil forms a separate layer. Subject: Science · Area: Matter & Materials · Ages 15 to 16 Page: https://lightmysky.com/learn/science/why-some-things-dissolve-and-others-do-not-mt__njIrlqqqL ## Ready when they can - Explain dissolving as an exchange of interactions rather than a disappearance - Predict whether a given solute will dissolve in water or in a non-polar solvent, and say why - Use supplied solubility limits to calculate the mass crystallised when an initially saturated solution cools to equilibrium, with unchanged water mass and water-free crystals ## Lesson: Why salt dives in and oil stays out You have compared attractions between molecules. Dissolving also involves a solvent, the liquid doing the dissolving. Sodium chloride contains ions held in a crystal. Polar water molecules attract these ions, separate them from the crystal and surround them. Attraction between an ion and a polar molecule is called ion-dipole attraction. The ions already existed in the solid. Water does not create them. *(drawing: The dissolved salt remains present as water-surrounded ions. These boxes describe the process, not molecular geometry.)* Essentially all dissolved sodium chloride separates into mobile ions, making it a strong electrolyte. Strong does not mean concentrated: conductivity also depends on how many ions are present. Sugar remains as neutral molecules and adds almost no conductivity to pure water. The solution's conductivity is not exactly zero. Compare similar concentrations with a supervised, battery-powered conductivity tester. Never use mains electricity or taste unknown solutions. Dissolving changes contacts among solute and solvent particles. Attractions and the tendency of particles to mix both matter. Water often dissolves ionic or polar solutes, but some ionic solids barely dissolve. Sugar can hydrogen-bond with water. Oil-water contacts do not favour extensive mixing, although oil and water do attract. Nonpolar solutes often dissolve better in nonpolar solvents. Similar polarity is a guide, not a guarantee. A saturated solution is at its equilibrium solubility limit. A supersaturated solution contains more dissolved solute than that limit at its temperature. Cooling can leave this temporary state without crystals forming. A seed crystal provides a surface for growth. In a supervised sodium acetate 'hot ice' demonstration, crystals can grow rapidly and release heat. This is an explanation to watch, not a home recipe. Hot liquids can burn; do not touch the liquid. A solubility curve plots temperature horizontally and the equilibrium solubility limit vertically. Check units, often grams of solute per 100 g water. For cooling, keep the water mass fixed. Find the cold capacity for that mass. If the actual initial dissolved mass is at or below this capacity, no solute crystallises. Otherwise subtract the cold capacity from that mass. This gives the crystal mass at equilibrium if no water is lost or enters the crystals. **Example.** The solubility limits are 50 g at 60°C and 30 g at 20°C per 100 g water. A hot saturated solution contains 50 g solute and 100 g water. It cools without water loss. At equilibrium, 30 g remains dissolved and 50 - 30 = 20 g crystallises, with no water in the crystals. For an unsaturated start, compare the actual dissolved mass with the cold capacity first. If it does not exceed that capacity, all the solute stays dissolved. **Recap.** Dissolving leaves solute particles in a solvent. Polarity guides predictions. Cooling calculations need stated units, a fixed solvent mass and a final equilibrium state. *Written for this dataset using chemistry and sodium acetate records as factual references. No source prose or preparation procedure was adapted.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Forces Between Molecules](https://lightmysky.com/learn/science/forces-between-molecules-mt_0uBZWotvZB) ## Optional connections - [Dissolving & Solutions](https://lightmysky.com/learn/science/dissolving-and-solutions-mt_Mf-T-fYRLX) ## Opens up - [Solubility Equilibria and When a Precipitate Appears](https://lightmysky.com/learn/science/solubility-equilibria-and-when-a-precipitate-appears-mt_IMdWLxIAFt)