Grade 7 Integrated Science MIXTURES, ELEMENTS AND COMPOUNDS – Mixtures Notes
Integrated Science — MIXTURES, ELEMENTS AND COMPOUNDS
Subtopic: Mixtures (Age 12, Kenya)
Learning goals:
- Explain what a mixture is.
- Differentiate homogeneous and heterogeneous mixtures with Kenyan examples.
- Name simple ways to separate mixtures and show how they work.
What is a mixture?
A mixture is made when two or more substances are put together but do not form a new substance. Each part keeps its own properties and can be separated by physical methods.
Everyday Kenyan examples
- Salt dissolved in water (sea water or salty water) — common example of a mixture.
- Tea with sugar — sugar dissolves in the water (homogeneous).
- Soil (sand, small stones, plant bits) — shows different visible parts (heterogeneous).
- Air — a mixture of gases (nitrogen, oxygen, etc.) and feels the same everywhere (homogeneous).
- Maize flour mixed with bits of bran — heterogeneous.
Types of mixtures
Looks the same all over. The parts are evenly mixed and you cannot see the separate parts. Example: sugar in tea, salt in water, air.
You can see different parts or layers. Example: soil, salad, oil and water (oil floats on water).
How to tell a mixture from a new substance
- In a mixture, each substance keeps its properties (salt still tastes salty).
- Mixtures can be separated by physical methods (no chemical change).
Methods to separate mixtures (simple and useful)
Simple safe experiments to try at home or in class
- Mix sugar in warm water (homogeneous). Evaporate to get sugar crystals.
- Mix sand and water. Use cloth to filter and separate sand (filtration).
- Mix oil and water. Observe two layers (heterogeneous). Try to separate using a spoon or pipette.
Quick safety and notes
- Always ask a teacher or adult before doing experiments.
- Use clean containers and avoid heating near open flame without supervision.
Summary
A mixture is a physical joining of two or more substances. They may be homogeneous (same throughout) or heterogeneous (different parts visible). Mixtures can be separated by physical methods like filtration, evaporation, sieving, magnetic separation and decantation.
Mini quiz (try these)
- Is salt water a mixture or a compound? (Answer below)
- Which method would you use to separate iron filings from sand?
- Name one homogeneous and one heterogeneous example from your home.
- Salt water is a mixture (salt is dissolved but not chemically changed).
- Magnetic separation (use a magnet).
- Examples will vary. Homogeneous: tea with sugar. Heterogeneous: soil with stones.
Prepared for Integrated Science learners (Kenya), age 12. Use these notes with classroom activities and teacher guidance.