--- title: "Choosing How to Separate Mixtures" description: "Choose separation techniques using physical properties: filtration for undissolved solids, distillation using vaporisation and condensation, crystallisation for dissolved solids, and chromatography fo" canonical: https://lightmysky.com/learn/science/choosing-how-to-separate-mixtures-mt_U_tJvy3cbB source: https://lightmysky.com/learn/science/choosing-how-to-separate-mixtures-mt_U_tJvy3cbB.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`. # Choosing How to Separate Mixtures Choose separation techniques using physical properties: filtration for undissolved solids, distillation using vaporisation and condensation, crystallisation for dissolved solids, and chromatography for components that travel differently Subject: Science · Area: Matter & Materials · Ages 11 to 13 Page: https://lightmysky.com/learn/science/choosing-how-to-separate-mixtures-mt_U_tJvy3cbB ## Ready when they can - Selects the correct separation technique for a given mixture with justification - Describes the steps of simple distillation and explains why it works - Interprets separated chromatography spots, recognises limits of spot counts, and calculates Rf values using distances measured from the same starting line - Explains why filtration removes sand from water but not salt ## Lesson: Choosing the right way to separate a mixture You have used sieving, filtering and evaporation. Filtration traps undissolved grains in suitable filter paper. Water and dissolved salt pass through because their particles are much smaller than its openings. To separate sand from a salt solution, filter out sand first. Ordinary filter paper cannot recover dissolved salt. Crystallisation recovers a dissolved solid as crystals. Evaporate some water from a salt solution until crystals begin to appear, then allow it to cool. Separate and dry the crystals. Some salt remains in the leftover solution. Use a filter funnel and paper for sand, then an evaporating dish for the solution. Heating needs teacher supervision. *(drawing: The condenser cools water vapour into liquid. Salt does not vaporise at the temperatures used.)* Simple distillation uses vaporisation followed by condensation. Water from a salt solution vaporises, then becomes liquid in a cooled condenser. Salt stays in the flask. With two liquids, both can enter the vapour, which is richer in the more volatile, usually lower-boiling liquid. Simple distillation works better when boiling points are far apart. It does not always give a pure liquid. This bar chart compares measured Rf values for separate dye spots. Count separate spots to find a minimum number of components detected in a sample. Each separate spot shows at least one component. The sample may contain more: components can overlap at one position, and some may not be visible. The chart compares results; it is not a drawing of the chromatography paper. In paper chromatography, place a dye spot on a pencil starting line above the solvent level. Rising solvent carries dyes different distances because they interact differently with solvent and paper. A submerged spot may wash off. Rf = spot distance / solvent-front distance. Measure both from the starting line, using the spot's centre. Rf is from 0 to 1 and depends on test conditions. Chromatography can also separate colourless substances. **Recap.** Filter undissolved solids, crystallise dissolved solids, distil by vaporising and condensing, and interpret chromatography using spots and Rf. *Lesson, questions and flashcards written for this dataset.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Separating Mixtures](https://lightmysky.com/learn/science/separating-mixtures-mt_2b6CB0w3Yx) - [Pure Substances & Mixtures](https://lightmysky.com/learn/science/pure-substances-and-mixtures-mt_MBTVB-E-S7) ## Opens up - [Potable Water and Treating Waste Water](https://lightmysky.com/learn/science/potable-water-and-treating-waste-water-mt_5qsFZJSmMO) - [Paper Chromatography and the Rf Value](https://lightmysky.com/learn/science/paper-chromatography-and-the-rf-value-mt_BAcCcz11ls) - [Crude Oil, Fractional Distillation and Cracking](https://lightmysky.com/learn/science/crude-oil-fractional-distillation-and-cracking-mt_Jg3O4EQ9Vz) - [Testing for Ions and Gases](https://lightmysky.com/learn/science/testing-for-ions-and-gases-mt_PDZjzQJdVt)