Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Define physical and chemical properties.
• Classify matter as solids, liquids, or gases.
• Describe the properties of metals and non-metals.
• Distinguish between pure substances and mixtures.
• Explain the difference between physical and chemical changes.

Lesson summary

This week, we delve into the fascinating world of matter and materials, focusing on their properties and how we classify them. Understanding these concepts is crucial because everything around us – from the food we eat to the buildings we live in – is made of matter. Knowing the properties of different materials allows us to choose the right materials for specific purposes, impacting everything from construction to technology. In South Africa, with our diverse industries and growing technological advancements, a strong foundation in material science is vital for future engineers, scientists, and informed citizens.

Lesson notes

2.1 Physical and Chemical Properties Physical Properties: These are characteristics of a substance that can be observed or measured without changing the substance's chemical identity.

Examples include: Colour: The visual appearance of a substance (e.g., gold is yellow).

Density: The mass per unit volume of a substance (e.g., water has a density of 1 g/cm³). Density is important in buoyancy - objects float if their density is less than the density of the liquid they're in. In South Africa, this is vital in industries like shipping and boat building.

Melting Point: The temperature at which a solid changes to a liquid (e.g., ice melts at 0°C).

Boiling Point: The temperature at which a liquid changes to a gas (e.g., water boils at 100°C). Altitude affects boiling point; water boils at a lower temperature at higher altitudes like in Lesotho.

Hardness: A measure of a substance's resistance to scratching or indentation (e.g., diamond is very hard).

Malleability: The ability of a solid to be hammered or rolled into thin sheets (e.g., gold is very malleable). This makes it useful for jewellery.

Ductility: The ability of a solid to be drawn into wires (e.g., copper is very ductile). This makes it ideal for electrical wiring in South African homes.

Conductivity: The ability of a substance to conduct electricity or heat (e.g., copper is a good conductor of electricity). Insulators resist conduction (like plastic coating on wires).

Solubility: The ability of a substance to dissolve in a solvent (e.g., sugar is soluble in water).

Chemical Properties: These describe how a substance reacts with other substances or changes into a new substance. These can only be observed when a substance undergoes a chemical change.

Examples include: Flammability: The ability of a substance to burn (e.g., petrol is flammable). Fire safety is important, especially in informal settlements in South Africa.

Reactivity with Acids: How readily a substance reacts with acids (e.g., some metals react with hydrochloric acid).

Corrosiveness: The ability of a substance to corrode or destroy other materials (e.g., strong acids are corrosive). Rusting of iron is a chemical change where iron reacts with oxygen and water. This is a major issue in South Africa's coastal regions due to the high humidity.

Oxidation: The ability of a substance to react with oxygen (e.g., iron rusts when exposed to oxygen and water). 2.2 Classification of Matter: States of Matter Matter exists in three common states: Solid: Has a fixed shape and volume. Particles are tightly packed and vibrate in fixed positions (e.g., a rock, a piece of wood, ice).

Liquid: Has a fixed volume but takes the shape of its container. Particles are close together but can move around (e.g., water, cooking oil, petrol).

Gas: Has no fixed shape or volume and expands to fill its container. Particles are widely spaced and move randomly (e.g., air, oxygen, carbon dioxide). 2.3 Properties of Metals and Non-metals Metals: Generally, metals are: Good conductors of heat and electricity: This makes them suitable for electrical wiring and cooking utensils.

Malleable: Can be hammered into thin sheets (e.g., aluminum foil).

Ductile: Can be drawn into wires (e.g., copper wires).

Lustrous: Have a shiny appearance (e.g., gold, silver). Solid at room temperature (except mercury, which is a liquid). Examples of metals used in South Africa include: Gold (for jewellery), Iron (for construction), Aluminum (for packaging).

Non-metals: Generally, non-metals are: Poor conductors of heat and electricity: This makes them suitable as insulators.

Brittle: Break easily when hammered (e.g., sulfur, carbon as graphite).

Dull: Lack a shiny appearance (except diamond, which is lustrous). Can be solids, liquids, or gases at room temperature (e.g., sulfur is a solid, bromine is a liquid, oxygen is a gas).

Examples of non-metals include: Oxygen (essential for respiration), Carbon (in coal and diamonds), Sulfur (used in the production of sulfuric acid). 2.4 Pure Substances and Mixtures Pure Substances: A pure substance contains only one type of particle. They have fixed compositions and properties. They can be either elements or compounds.

Elements: Substances that cannot be broken down into simpler substances by chemical means (e.g., gold (Au), oxygen (O2), iron (Fe)). These are found on the periodic table.

Compounds: Substances formed when two or more elements are chemically combined in a fixed ratio (e.g., water (H2O), sodium chloride (NaCl – table salt), carbon dioxide (CO2)).

Mixtures: A combination of two or more substances that are physically combined, not chemically bonded. The substances in a mixture retain their individual properties.

Homogeneous Mixtures: Mixtures that have a uniform composition throughout (e.g., salt water, air, sugar dissolved in water). These are also called solutions.