You stir a spoonful of salt into water and it disappears completely. Salad dressing splits into layers all by itself. A magnet pulls metal right out of sand. What's going on?
By the end of this lesson, you will be able to:
Click a card to reveal what each word means. Click it again to close. You'll meet every one of these in the lesson below.
No lab needed for this one - your kitchen is already full of strange behavior. Look closely at these three everyday items.
Imagine zooming in on a sample of matter until you can see its particles. In some samples, every single particle is identical - the same ingredient, everywhere you look.
A pure substance is a sample of matter that has the same ingredients throughout. Pure substances have only one type of particle: an element, a molecule, or a compound.
Pure substances you might recognize:
Back to the salad dressing from the mystery. The oil and vinegar were shaken together - but did they ever truly become one new substance?
The particles stay separate - they never chemically join. A mixture contains different particles that are not chemically joined. Because the parts never joined, they can be separated physically. In salad dressing, the oil and vinegar can be physically separated by density: the less dense oil floats to the top and forms its own layer.
Compare the two beakers below. Both hold mixtures - but look at how the particles are spread out. Follow the color coding: green is homogeneous and orange is heterogeneous.
Mixtures can be separated physically - no chemistry required. Here are four tools, each matched to a different kind of mixture. The trick is choosing the tool that targets a difference between the parts: size, state, or magnetism.
How do you pick the right tool? Watch one worked example, step by step. Mixture: muddy water (dirt + water).
You started this lesson with three strange kitchen items. Now you can explain every one of them like a chemist.
Everything from this lesson in one place: the words to know and the goals you worked toward.
| Term | Student-Friendly Definition |
|---|---|
| Pure substance | A sample of matter that has the same ingredients throughout - only one type of particle (element, molecule, or compound). |
| Mixture | Different particles that are not chemically joined. The parts can be separated physically. |
| Homogeneous mixture | Different substances that are evenly distributed ("homo" = one or same throughout). Example: coffee. |
| Heterogeneous mixture | Different substances that are UNevenly distributed ("hetero" = many different parts you can see). Example: chicken soup. |
| Filtration | Separates big particles from small particles using a filter (like a coffee filter). |
| Evaporation | Removes a liquid by turning it into gas, leaving solids behind. |
| Magnetism | Separates a mixture when one part is magnetic and the others are not. |
| Sieving | Separates mixtures using a tool with holes of a specific size (a sieve or mesh). |
| Learning Goals | How You Showed It |
|---|---|
| Classify matter as a pure substance, homogeneous mixture, or heterogeneous mixture (6.MS-PS1-8(MA)). | You read particle diagrams of elements, molecules, and compounds, then sorted five real mixtures by asking whether their parts were spread evenly or unevenly. |
| Choose the right physical method to separate a mixture into its parts (6.MS-PS1-8(MA)). | You used the three-step plan (name the parts, find a difference, match the tool) to separate four mixtures with filtration, evaporation, magnetism, and sieving. |
Five questions covering everything you discovered, including new samples to classify and new mixtures to separate. Answer every question, then submit.
Pure substances and mixtures connect to everything else in the matter unit. Extension challenges: design a separation plan for trail mix that has iron-fortified cereal in it (hint: you'll need more than one tool). Or hunt through your kitchen and classify five items as pure substance, homogeneous mixture, or heterogeneous mixture - then defend each call to a partner.