Understanding Pure Substances and Mixtures in Science

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Explore the concepts of pure substances and mixtures in science, distinguishing between them and understanding their particle theory. Learn about mechanical mixtures and solutions, and discover why apple juice is classified as a mixture. Delve into the classification of mixtures and the states of solutions.

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Grade 7 Science - Willis Pure Substances and Mixtures Lesson 2

Learning Goals I can distinguish between pure substances and mixtures. I can use the particle theory to describe the difference between pure substances and mixtures. I can distinguish between solutions and mechanical mixtures.

Pure Substances and Mixtures Pure substances: matter that contains only one kind of particle E.g.: tin foil, table sugar, distilled water, salt Mixture: matter than contains two or more pure substances mixed together E.g.: salt water, batteries, milk, air

Pure Substances and Mixtures Is apple juice a pure substance or a mixture? Discuss (Answer next page)

Pure Substances and Mixtures Apple juice is a mixture of water particles, sugar particles, flavourparticles and vitamin particles all mixed together.

Mechanical Mixtures and Solutions Scientists classify mixtures into two main groups: 1. Mechanical Mixtures (also called heterogeneous mixture): a mixture with different parts that you can see. E.g.: cereal bars, omelettes, cookies 2. Solutions (also called homogeneous mixture): a mixture that looks like a single pure substance uniform in appearance. E.g. tea, salt water, paint

Mechanical Mixtures and Solutions Solutions can be in any three states: solid, liquid or gas, but only one state is visible at a time. Mechanical mixtures can include different states in one mixture. (Think of breakfast cereal!)

Particles of Mixtures It may surprise you that clear apple juice, air and steel are homogeneous mixtures, not pure substances! Why? In a solution, the different kinds of particles are mixed together evenly. In a mechanical mixture, the different kinds of particles stay together in groups and are distributed unevenly. As a result, when you look at a mechanical mixture you can usually see the different kinds of matter.