Mixtures
Mixtures as combinations of pure substances
Talking Science
In our last lesson, we talked about pure substances, but we also said that in nature, most things are actually made by mixing two or more pure substances.
That's right. So what do we call substances that are mixtures of pure substances?
We call them mixtures. I didn’t forget!
I knew you'd remember. So today we’ll dive deeper into mixtures. Anything specific you want to know?
Sara: First off, how can I tell if something is a pure substance or a mixture?
Mark: Good question! Sometimes it’s really easy. For example, if you can clearly see different parts that are different colors or states, it's a mixture.
Sara: So sometimes it’s not that obvious? Maybe when the substances are mixed so well that we can’t tell them apart?
Mark: Exactly! And that’s where we get to two types of mixtures — based on how well things are mixed.
Sara: I'm listening!
Mark: If the substances are not perfectly mixed and you can still see the different parts, or if the composition isn’t the same throughout, it’s called a HETEROGENEOUS MIXTURE.
Sara: So things like sand, chocolate with nuts, and fizzy drinks would be heterogeneous mixtures?
Mark: Exactly! Most mixtures around us are like that. But if the substances are mixed so well that we can't tell them apart, and the composition is the same everywhere — then it's a HOMOGENEOUS MIXTURE.
Sara: I’ve heard the words "homogeneous" and "heterogeneous" before, not just in chemistry.
Mark: Yep! "Homogeneous" means uniform — the same all the way through, while "heterogeneous" means varied or different in different parts.
Sara: Got it. Let me guess — homogeneous mixtures are less common in nature because it's harder to get everything that perfectly mixed?
Mark: You're spot on. In nature, homogeneous mixtures are rarer. Examples would be clear solutions, like seawater, or mixtures of gases like air.
Sara: That makes sense. Like how in a glass of seawater we can’t see the salt, and it tastes the same throughout.
Mark: And both types — homogeneous and heterogeneous — can be found in all three states of matter.
Key Science Concepts
Let’s wrap this up. Mixtures — combinations of pure substances — can be either homogeneous or heterogeneous. Sara even drew how she imagines particles are arranged in each type.
| Homogeneous Mixtures | Heterogeneous Mixtures |
|---|---|
 |
 |
| Particles cannot be seen with the naked eye or under a microscope | You can often see the different parts, even without a microscope |
| The mixture is the same all the way through | The mixture is not uniform — it changes from part to part |
| Examples: air, seawater | Examples: soil, sand |
- Homogeneous mixture
- A mixture where every part has the same composition and properties.
- Heterogeneous mixture
- A mixture where the composition and properties are not the same throughout.
Science Fun Fact
Milk may look like a homogeneous mixture, but it's not!
Milk — a sneaky heterogeneous mixture
Even though it looks like a perfectly uniform liquid, milk is actually a heterogeneous mixture. It contains water, fat, proteins, and other ingredients that are well blended but not fully dissolved. Tiny fat droplets float in the water, making milk an emulsion — a special type of heterogeneous mixture. That’s why milk can spoil without immediately changing its appearance!
Quick Science Quiz
...