Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define mixture, solution, solute, solvent, and suspension.
• Describe and apply methods like filtration, sieving, and evaporation.
• Select the best separation technique for a given mixture.
• Explain how distillation separates solutions.
• Understand the importance of separating mixtures in daily life.

Lesson summary

Mixtures and solutions are all around us! Think about the air we breathe (a mixture of gases), the sea water at Durban beach (a solution of salt and water), or even the sand we play in (a mixture of different sized particles). But sometimes we need to separate these mixtures and solutions to get the individual components. Maybe we want to purify water for drinking, extract gold from ore, or separate different coloured dyes for creating fabrics. Understanding how to separate mixtures and solutions is crucial in many areas, from household tasks to large-scale industries in South Africa. This knowledge helps us to conserve resources, improve water quality, and create useful products.

Lesson notes

Let's delve into the key concepts: Mixture: A combination of two or more substances that are physically combined but not chemically bonded. Each substance retains its individual properties.

Examples include: Soil: A mixture of sand, silt, clay, humus (decomposed organic matter), air, and water.

Salad: A mixture of lettuce, tomatoes, cucumbers, and dressing.

Concrete: A mixture of cement, sand, gravel, and water.

Air: A mixture of gases, primarily nitrogen, oxygen, argon, and carbon dioxide.

Solution: A special type of mixture where one substance (the solute) dissolves evenly into another substance (the solvent). The solute is dispersed at a molecular level. Solutions are homogeneous (uniform throughout).

Solute: The substance that dissolves. Examples include salt, sugar, and coffee granules.

Solvent: The substance that does the dissolving. Water is often called the "universal solvent" because it dissolves many substances. Other solvents include ethanol (alcohol) and acetone.

Example: Sugar dissolving in water. Sugar is the solute, and water is the solvent.

Suspension: A heterogeneous mixture containing solid particles that are large enough to be seen with the naked eye and that settle out over time. Suspensions are cloudy or opaque.

Example: Muddy water. The soil particles are suspended in the water, but they will eventually settle to the bottom.

Example: A mixture of flour and water.

Separation Techniques: Filtration: Separating insoluble solids from a liquid by using a filter paper. The liquid (filtrate) passes through the filter paper, while the solid (residue) remains on the filter paper.

Example: Removing sand from water.

South African Context: Filtering river water using a cloth or filter paper to remove visible dirt and debris before further purification.

Sieving: Separating solids of different sizes using a sieve (a mesh screen). The smaller particles pass through the sieve, while the larger particles are retained.

Example: Separating gravel from sand.

South African Context: Miners use sieves to separate gold particles from sand and gravel.

Evaporation: Separating a soluble solid from a liquid solution by heating the solution until the liquid evaporates, leaving the solid behind.

Example: Obtaining salt from saltwater.

South African Context: Traditional salt pans along the coast use evaporation to produce salt from seawater.