--- marp: true theme: default html: true --- # Distillation and chromatography Year 7 Chemistry · Pure substances and mixtures --- ## Today **We are learning to** distillation collects a liquid by boiling and condensing it; chromatography separates dissolved substances such as dyes. Explain each principle and when distillation beats evaporation. - I can describe the principle of distillation and of chromatography. - I can name a mixture each technique suits. - I can explain when distillation is used instead of evaporation. --- ## Why it matters > Ships at sea make fresh water by boiling seawater and catching the steam. Forensic scientists find out which pen wrote a note by letting water creep up a strip of paper. --- 💬 Discussion ## Engage: predict **Seawater is heated in a flask. A tube carries the steam through a cold jacket into a second, empty flask. What collects in the second flask?** - Nothing - Salty water - Fresh water - Salt --- ✍️ Activity ## Explore it {{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry%2Fdistil-chroma%2Fstep-2&code=widget%3A+distil%0A}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry/distil-chroma/?full=step-2#step-2) --- ✅ Check ## What happened? * Fresh water. Only water particles boil off; the salt stays behind in the first flask. --- ✅ Check ## Compare **Both techniques heat a liquid until it turns to gas. Sort each statement.** Groups: Evaporation only · Distillation only · Both Uses the difference in boiling point · Needs heat · The vapour escapes into the air · The vapour is cooled and collected as a liquid · You end up with only the solid · You end up with the liquid and the solid · Needs a condenser and a collecting flask * Answer: Uses the difference in boiling point → Both; Needs heat → Both; The vapour escapes into the air → Evaporation only; The vapour is cooled and collected as a liquid → Distillation only; You end up with only the solid → Evaporation only; You end up with the liquid and the solid → Distillation only; Needs a condenser and a collecting flask → Distillation only --- ✅ Check ## The dyes **Why do the dyes in the ink end up at different heights?** - The dyes evaporate at different speeds - Heavier dyes sink lower - The water makes new colours as it rises - Each dye dissolves in the water and sticks to the paper differently, so the water carries each one a different distance * Answer: Each dye dissolves in the water and sticks to the paper differently, so the water carries each one a different distance --- ✅ Check ## Which technique suits? **Match each job to the technique that suits it.** | | | |---|---| | `Get drinking water from seawater` | A. Evaporation | | `Get salt from seawater, letting the water go` | B. Distillation | | `Find out which dyes are in a black ink` | C. Chromatography | | `Get sand out of sandy water` | D. Filtration | * Answer: Get drinking water from seawater → B. Distillation; Get salt from seawater, letting the water go → A. Evaporation; Find out which dyes are in a black ink → C. Chromatography; Get sand out of sandy water → D. Filtration --- ✅ Check ## Mix it up **Looking back at heating curves: water in a flask is boiling and the heat stays on full. What does a thermometer in the water show over the next few minutes?** - It goes up and down - It drops, because the water is turning to steam - It stays at about 100 °C - It keeps rising * Answer: It stays at about 100 °C --- ✅ Check ## Elaborate: distillation or evaporation? **Both use the same property. Which would you choose?** Groups: Evaporation · Distillation A salt farm wants salt from seawater. · A ship needs drinking water from seawater. · A lab wants very pure water with nothing dissolved in it. · You want sugar crystals from sugar syrup. · You want to keep both the water and the salt from a salt solution. * Answer: A salt farm wants salt from seawater. → Evaporation; A ship needs drinking water from seawater. → Distillation; A lab wants very pure water with nothing dissolved in it. → Distillation; You want sugar crystals from sugar syrup. → Evaporation; You want to keep both the water and the salt from a salt solution. → Distillation --- ✅ Check ## Elaborate: three techniques, three properties **Which property does each technique use?** Groups: Boiling point · How well each substance dissolves and sticks to the paper · How much solid can stay dissolved Crystallisation: a hot, concentrated solution is left to cool, and crystals form. · Chromatography: food colourings separate on paper. · Distillation: alcohol is separated from water. * Answer: Crystallisation: a hot, concentrated solution is left to cool, and crystals form. → How much solid can stay dissolved; Chromatography: food colourings separate on paper. → How well each substance dissolves and sticks to the paper; Distillation: alcohol is separated from water. → Boiling point --- ✅ Check ## Elaborate: First Nations knowledge and plant oils **Which property or process does each step use?** Groups: Breaking up the leaves so substances can get out · Some substances dissolve in water · The oil is carried away with steam, then condensed · The oil floats on the water Crushing tea tree leaves · Soaking crushed leaves in water · Modern steam distillation: steam passes through the leaves · Modern steam distillation: separating the collected liquid * Answer: Crushing tea tree leaves → Breaking up the leaves so substances can get out; Soaking crushed leaves in water → Some substances dissolve in water; Modern steam distillation: steam passes through the leaves → The oil is carried away with steam, then condensed; Modern steam distillation: separating the collected liquid → The oil floats on the water --- ✅ Check ## Blue **The blue spot moved 8.0 cm. What is its Rf value?** * Answer: 0.8 --- ✅ Check ## Red **The red spot moved 5.0 cm. What is its Rf value?** * Answer: 0.5 --- ✅ Check ## Unknown dye **An unknown dye has Rf = 0.50 in the same setup. Which dye could it be?** - The red dye - The blue dye - None of them * Answer: The red dye --- ✅ Check ## One spot **A green ink gives just one spot. What can you conclude?** - It is definitely a pure substance - The test failed - It is probably one dye, but two dyes with the same Rf value would also give one spot * Answer: It is probably one dye, but two dyes with the same Rf value would also give one spot --- ## Evaluate: look back What did you think would collect in the second flask? Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - Distillation separates a liquid from what is dissolved in it by boiling the liquid and cooling the vapour back into a liquid somewhere else. - Evaporation and distillation use the same property (boiling point), but distillation collects the vapour and evaporation lets it escape. - Chromatography separates a mixture of dissolved substances, such as dyes, because each is carried a different distance. - Distillation suits seawater (to get water). Chromatography suits inks, food colourings and plant pigments. --- ✅ Check ## Exit ticket **Why would a ship use distillation, not evaporation, to get drinking water from seawater?** * Distillation collects the water vapour as liquid; evaporation lets it escape and keeps only the salt.