Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define and differentiate between mixtures and solutions.
• Identify various methods for separating mixtures.
• Apply your knowledge to separate simple mixtures.
• Explain evaporation for obtaining salt from seawater.
• Describe how filtration is used to purify water.

Lesson summary

This week, we delve into the fascinating world of separating mixtures and solutions! Mixtures are combinations of different substances that are physically combined but not chemically bonded. Solutions are special types of mixtures where one substance (the solute) dissolves completely into another (the solvent). Understanding how to separate these is crucial because many materials we use daily are mixtures, and we often need to isolate specific components for various purposes, from cleaning our water to extracting valuable minerals.

Lesson notes

A mixture is a combination of two or more substances that are physically combined, meaning they are not chemically bonded. The components of a mixture retain their individual properties. Mixtures can be homogeneous (uniform composition throughout, like air) or heterogeneous (non-uniform composition, like a salad). A solution is a special type of homogeneous mixture where one substance (the solute) dissolves completely into another substance (the solvent). For example, sugar dissolving in water. The solute particles are evenly distributed throughout the solvent, and the mixture appears uniform. Now, let’s explore different methods for separating mixtures: Hand Sorting: Description: This is the simplest method, involving physically picking out the different components of a mixture by hand.

Best Used For: Mixtures with large, easily distinguishable components.

Example: Separating different coloured sweets in a bowl, removing stones from rice.

South African Relevance: Removing weeds from a garden.

Sieving: Description: This method uses a sieve (a mesh with holes) to separate substances based on particle size. Smaller particles pass through the sieve, while larger particles are retained.

Best Used For: Separating mixtures of solids with different particle sizes.

Example: Separating flour from bran.

South African Relevance: Sifting maize meal to remove larger bits.

Filtration: Description: This method uses a filter medium (like filter paper) to separate insoluble solids from a liquid. The liquid passes through the filter paper as the filtrate, while the solid remains on the filter paper as the residue.

Best Used For: Separating insoluble solids from liquids.

Example: Separating sand from water.

South African Relevance: Filtering water from a river or dam (though further treatment is always required for safe drinking water).

Evaporation: Description: This method is used to separate a soluble solid from a liquid. The solution is heated, causing the liquid (the solvent) to evaporate, leaving the solid (the solute) behind.

Best Used For: Separating a dissolved solid from a liquid.

Example: Obtaining salt from seawater.

South African Relevance: Salt production, often seen along coastal regions.