--- marp: true theme: default html: true --- # Mixed, not joined? Year 8 Chemistry · Elements and compounds --- ## Today **We are learning to** a mixture is two or more substances mingled together but not chemically joined. Each keeps its own properties, the amounts can vary, and the parts can be separated by physical means. A compound is the opposite: atoms joined in a fixed ratio, with new properties. - I can explain what a mixture is. - I can tell a mixture from a compound. - I can sort substances into elements, compounds and mixtures. --- ## Why it matters > You breathe in oxygen and nitrogen with every breath, yet only the oxygen keeps you alive. In air, oxygen still behaves exactly like oxygen. --- 💬 Discussion ## Engage: predict **Air is about one fifth oxygen. Is the oxygen in air still oxygen, with oxygen's properties?** - Only some of it - No: mixing with nitrogen turned it into a new substance - No: air is one compound called 'air' - Yes: in a mixture each substance keeps its own particles and properties --- ✍️ Activity ## Explore it {{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-8%2Fmixtures%2Fstep-2&code=widget%3A+atoms%0Ashow%3A+N2+x8%2C+O2+x3%2C+Ar+x1%2C+CO2+x1%0Acaption%3A+A+tiny+sample+of+air%2C+enlarged+millions+of+times.%0A}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-8/mixtures/?full=step-2#step-2) --- ✅ Check ## What happened? * Yes. Air is a mixture: the oxygen particles are mingled with nitrogen and others, but not joined to them. That is why your lungs can take oxygen out of air. --- ✅ Check ## What a mixture is **What is a mixture?** - Two or more substances mingled together but not chemically joined - Two or more types of atom joined in a fixed ratio - Any substance with more than one atom in each particle * Answer: Two or more substances mingled together but not chemically joined --- ✅ Check ## Mixture or compound **Mixture or compound?** Groups: Mixture · Compound Each part keeps its own properties · New properties, unlike its elements · The amounts can be anything · A fixed ratio of atoms · Separated by filtering, evaporating or distilling · Separated only by a chemical reaction * Answer: Each part keeps its own properties → Mixture; New properties, unlike its elements → Compound; The amounts can be anything → Mixture; A fixed ratio of atoms → Compound; Separated by filtering, evaporating or distilling → Mixture; Separated only by a chemical reaction → Compound --- ✅ Check ## Three kinds **Element, compound or mixture?** Groups: Element · Compound · Mixture Oxygen · Water · Air · Salt water · Carbon dioxide · Copper * Answer: Oxygen → Element; Water → Compound; Air → Mixture; Salt water → Mixture; Carbon dioxide → Compound; Copper → Element --- ✅ Check ## Getting it back **How could you get the salt back from salt water?** - You can't: salt and water have joined - Evaporate the water: the salt is left - Filter it * Answer: Evaporate the water: the salt is left --- ✅ Check ## Solutions, suspensions and colloids **Three kinds of mixture. Match each to an example and what it does.** | | | |---|---| | `Solution` | A. Milk: tiny drops spread through; it looks cloudy but nothing settles | | `Suspension` | B. Salt water: the salt dissolves, the liquid stays clear and nothing settles | | `Colloid` | C. Muddy water: bits of solid spread through, then settle if left to stand | * Answer: Solution → B. Salt water: the salt dissolves, the liquid stays clear and nothing settles; Suspension → C. Muddy water: bits of solid spread through, then settle if left to stand; Colloid → A. Milk: tiny drops spread through; it looks cloudy but nothing settles --- ✍️ Activity ## Elaborate: any amount {{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-8%2Fmixtures%2Fstep-4&code=widget%3A+atoms%0Ashow%3A+H2+x10%2C+O2+x2%0Acaption%3A+A+mixture+with+lots+of+hydrogen.%0A}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-8/mixtures/?full=step-4#step-4) --- ✅ Check ## Both mixtures? **Both boxes hold hydrogen and oxygen in very different amounts. Are they both mixtures of hydrogen and oxygen?** - No: only one of them has the right amounts - No: they are two different compounds - Yes: a mixture can have its parts in any amounts * Answer: Yes: a mixture can have its parts in any amounts --- ✍️ Activity ## Elaborate: humid air {{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-8%2Fmixtures%2Fstep-5&code=widget%3A+atoms%0Ashow%3A+N2+x8%2C+O2+x2%2C+H2O+x4%0Acaption%3A+Humid+air+on+a+rainy+day.%0A}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-8/mixtures/?full=step-5#step-5) --- ✅ Check ## Compound or mixture **Humid air has water vapour in it. Water is a compound. Is humid air a compound?** - It is an element - Yes: it contains a compound - No: it is a mixture of elements and a compound, none joined to each other * Answer: No: it is a mixture of elements and a compound, none joined to each other --- ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - A **mixture** is two or more substances mingled together but not chemically joined. Each keeps its own particles and properties. - A mixture's parts can be in any amounts; a **compound** always has a fixed ratio (H₂O). - Mixtures can be separated by physical means (filtering, evaporating, distilling); compounds only by chemical reactions. - Air and salt water are mixtures; water and carbon dioxide are compounds. --- ✅ Check ## Exit ticket **Iron and sulfur are mixed, then heated to make iron sulfide. Which is the mixture and which the compound, and how could you tell with a magnet?** * Before heating: a mixture (a magnet pulls out the iron). After: iron sulfide, a compound (the iron is joined to sulfur, so a magnet can't pull it out).