Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define solute, solvent, solution, and suspension.
• Describe properties of materials and their uses.
• Demonstrate methods for separating mixtures.
• Identify real-life applications of separation techniques.
• Predict outcomes of experiments.

Lesson summary

This week, we delve into the fascinating world of materials and mixtures, focusing on how their properties influence their uses and how we can separate mixtures. Understanding these properties is crucial in our daily lives. From choosing the right materials to build our homes to separating valuable resources from waste, the knowledge of materials and mixtures is essential. In South Africa, understanding these concepts can help us utilize our natural resources sustainably and develop innovative solutions for challenges like water purification and waste management.

Lesson notes

2. 1.

Key Definitions: Mixture: A combination of two or more substances (elements or compounds) that are physically combined but not chemically bonded. Each substance retains its individual properties.

Think of a salad: you can still identify the lettuce, tomato, and cucumber.

Solute: The substance that dissolves in a solvent to form a solution.

Example: Sugar dissolving in water.

Solvent: The substance that dissolves a solute to form a solution.

Example: Water dissolving sugar.

Solution: A homogeneous mixture where the solute is evenly distributed throughout the solvent and cannot be seen separately.

Example: Sugar dissolved completely in water. The sugar particles are no longer visible.

Suspension: A heterogeneous mixture where the solute particles are large enough to be seen and will settle out over time.

Example: Sand mixed with water. The sand particles will eventually sink to the bottom. A good South African example is "mageu" that has been left to stand for a while; the thicker particles settle at the bottom. 2.

2. Properties of Materials: Different materials have different properties that make them suitable for different uses.

Some important properties include: Hardness: The ability of a material to resist scratching or indentation. Diamond is very hard, while talc is very soft. Think of the hard granite countertops used in some homes versus the softer wood used for furniture.

Flexibility: The ability of a material to bend without breaking. Rubber is very flexible, while glass is not. Consider the flexible rubber hoses used in gardens versus the rigid metal pipes used for plumbing.

Strength: The ability of a material to withstand force without breaking. Steel is very strong, while paper is not. Steel is used to build bridges, while paper is used for writing.

Conductivity: The ability of a material to conduct heat or electricity. Metals are generally good conductors, while plastic and wood are not. Copper wires are used to carry electricity, while plastic is used to insulate them.

Transparency: The ability of a material to allow light to pass through it. Glass is transparent, while wood is opaque. Windows are made of glass, while walls are made of wood or brick.

Density: The mass of a material per unit volume. Density determines whether an object will float or sink in a liquid. For example, wood floats on water because it is less dense than water, while a rock sinks because it is denser than water. 2.

3. Methods of Separating Mixtures: Different methods can be used to separate mixtures, depending on the properties of the components: Filtration: Separates solid particles from a liquid by passing the mixture through a filter. The solid particles are trapped by the filter, while the liquid passes through.

Example: Using a coffee filter to separate coffee grounds from brewed coffee.

Evaporation: Separates a dissolved solid from a liquid by heating the mixture until the liquid evaporates, leaving the solid behind.

Example: Obtaining salt from seawater by evaporating the water.

Decantation: Separates a liquid from a solid that has settled at the bottom of the container by carefully pouring off the liquid, leaving the solid behind.

Example: Separating muddy water by allowing the mud to settle and then pouring off the clear water.

Sieving: Separates solids of different sizes using a sieve.

Example: Separating sand from gravel using a sieve. This is common on construction sites in South Africa.

Magnetic Separation: Separates magnetic materials from non-magnetic materials using a magnet.

Example: Separating iron filings from sand using a magnet. This technique is used in recycling plants to separate metals from other waste. 2.

4. Worked

Examples: Example 1: A farmer in KwaZulu-Natal has a mixture of sand and mielies (corn). Which method would be best to separate the sand and mielies? Explain your reasoning.

Solution: Sieving would be the best method. Mielies and sand have different particle sizes. Using a sieve with appropriate sized holes will allow the sand to pass through while the mielies remain on the sieve.

Example 2: You have a glass of muddy water. Describe the steps you would take to obtain relatively clean water.

Solution: Decantation: Allow the muddy water to stand undisturbed for a period. The heavier mud particles will settle at the bottom of the glass.

Filtration: Carefully pour the water from the top of the glass through a filter paper placed in a funnel. This will remove any remaining fine particles of mud. The clear water that passes through the filter is called the filtrate.

Example 3: After heavy rains, a river in Limpopo has a lot of soil particles suspended in the water. Explain why this is a suspension and not a solution.

Solution: A suspension is a mixture where the particles are large enough to be seen and eventually settle out. In this case, the soil particles in the river water are visible (making the water appear cloudy) and will eventually settle to the bottom of the riverbed.