--- title: "Why Some Things Dissolve and Others Do Not" description: "Dissolving replaces the forces holding a solute together with forces between solute and solvent, and it only happens when that trade is worth making. This is why salt and sugar go into water but oil d" 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: 2026-09-12 --- > **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 replaces the forces holding a solute together with forces between solute and solvent, and it only happens when that trade is worth making. This is why salt and sugar go into water but oil does not. 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 - Read a solubility curve and use it to predict what crystallises when a solution cools ## Lesson: Why salt dives in and oil stays out Dissolving is a trade of pulls, not a vanishing act. Solid salt is sodium and chloride ions locked in a crystal. In water, the water molecules pull the ions apart and surround each one. The salt traded the attractions of its crystal for new attractions with water. Salt splits into free ions, so its solution carries current and we call it a strong electrolyte. Sugar also dissolves, but its molecules stay whole and uncharged, so sugar water carries no current at all. Water is polar, so it grips polar and ionic things like salt and sugar. Oil is nonpolar, and water cannot get a grip on it, so oil will not make the trade. That is the whole guide: matching pulls mix, mismatched pulls do not. A nonpolar solid therefore belongs in a nonpolar solvent, not in water. Before you mix, name the pulls on both sides and check they match. **Example.** You can even make salt from vinegar and baking soda: sodium acetate. Hot water holds far more of it than cold water does. Dissolve as much as possible while hot, then cool the liquid slowly without shaking it. The cold water now holds more than it normally should, which is called supersaturated. Touch it with one crystal and the extra salt crashes out in seconds, feeling warm as it hardens. This is the hot ice trick. **Tip.** A solubility curve simply plots how much water holds at each temperature. Suppose a curve reads 50 grams at 60 degrees and 30 grams at 20 degrees. A 50 gram load cooled from 60 to 20 must drop 20 grams as crystals. To predict any case, read the hot limit, read the cold limit, and subtract. **Recap.** Dissolving trades one set of pulls for another, so only matching pulls mix. ## 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) - [Dissolving & Solutions](https://lightmysky.com/learn/science/dissolving-and-solutions-mt_Mf-T-fYRLX) - [Concentration of Solutions in Moles per Cubic Decimetre](https://lightmysky.com/learn/science/concentration-of-solutions-in-moles-per-cubic-decimetre-mt_vRK78ynnXb) ## Opens up - [Solubility Equilibria and When a Precipitate Appears](https://lightmysky.com/learn/science/solubility-equilibria-and-when-a-precipitate-appears-mt_IMdWLxIAFt)