Lesson Notes By Weeks and Term v5 - Grade 9

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Differentiate between mixtures and compounds.
• Describe methods of separating mixtures.
• Identify reactants and products in chemical reactions.
• Classify different types of chemical reactions.
• Explain the conservation of mass.

Lesson summary

This week, we delve deeper into the fascinating world of matter and how it changes. We'll be focusing on compounds, mixtures, and chemical reactions, building upon the foundational knowledge you've already gained about atoms, elements, and the Periodic Table. Understanding these concepts is crucial, not only for excelling in Natural Sciences, but also for understanding the world around you. From cooking in your kitchen to the air you breathe, compounds, mixtures and reactions are happening constantly.

Think about braaing: The wood burning is a chemical reaction, the spices you mix are a mixture, and water is a compound essential to life.

Lesson notes

2.1 Compounds vs.

Mixtures Compounds: A compound is a substance formed when two or more different elements are chemically bonded together in a fixed ratio. This bonding involves the sharing or transfer of electrons between atoms. Because the elements are chemically bonded, compounds have completely different properties from their constituent elements. Compounds cannot be separated by physical means; only chemical reactions can break the bonds holding the elements together. Water (H₂O) and table salt (sodium chloride, NaCl) are common examples.

Example: Water (H₂O) is a compound made of hydrogen and oxygen. Hydrogen and oxygen are both flammable gases, but when they combine to form water, the resulting compound is a liquid that extinguishes fires.

Fixed Ratio: This is key! Water always has two hydrogen atoms for every one oxygen atom. NaCl always has one sodium atom for every one chlorine atom.

Mixtures: A mixture is a combination of two or more substances (elements or compounds) that are physically combined, but not chemically bonded. The substances in a mixture retain their individual properties, and they can be present in varying ratios. Mixtures can be separated by physical means because there are no chemical bonds holding them together.

Example: Imagine a handful of 'mixed nuts'. You have peanuts, cashews, almonds, and so on. They are physically combined, but each nut retains its own characteristics. You can pick them out individually. This is a mixture.

Variable Ratio: You can have a mixed nut with primarily peanuts, or one with primarily cashews. The ratio can vary.

Types of Mixtures: Homogeneous mixtures: These mixtures have a uniform composition throughout. You can't see the different components with the naked eye.

Examples include: Air (a mixture of nitrogen, oxygen, and other gases) Saltwater (salt dissolved in water) Sugar dissolved in water Heterogeneous mixtures: These mixtures have a non-uniform composition, and you can easily see the different components.

Examples include: Sand and gravel Oil and water "Samp and beans" (Umngqusho) – a traditional South African dish. 2.2 Methods of Separating Mixtures Since mixtures are not chemically bonded, they can be separated using physical methods.

Here are some common techniques: Filtration: Separates insoluble solids from a liquid using a filter paper. The solid remains on the filter paper (the residue), and the liquid passes through (the filtrate).

Example: Filtering muddy water to remove the soil particles. This is crucial in South Africa for accessing clean water sources.

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

Example: Obtaining salt from seawater by evaporating the water. This is how some salt companies in South Africa produce their products.

Distillation: Separates liquids with different boiling points. The mixture is heated, and the liquid with the lower boiling point evaporates first. The vapor is then cooled and condensed back into a liquid.

Example: Separating alcohol from water in the production of alcoholic beverages.

Magnetism: Separates magnetic materials from non-magnetic materials using a magnet.

Example: Removing iron filings from a mixture of sand and iron filings. This can be used in recycling processes to separate magnetic metals.

Decantation: Separating a liquid from an insoluble solid by carefully pouring the liquid off the top after the solid has settled.

Example: After making Umngqusho, you can let the beans settle and carefully pour off the excess cooking water.

Chromatography: Separates substances based on their different affinities for a stationary and mobile phase. (This is more advanced but is important for scientific testing) 2.3 Chemical Reactions A chemical reaction is a process that involves the rearrangement of atoms and molecules to form new substances. In other words, it's the breaking and forming of chemical bonds.

Reactants: The substances that are present at the beginning of a chemical reaction.

Products: The substances that are formed as a result of the chemical reaction.

Chemical Equation: A symbolic representation of a chemical reaction using chemical formulas and symbols.

Word Equation: A simple description of a chemical reaction using the names of the reactants and products.

For example: Methane + Oxygen → Carbon dioxide + Water Observable Changes During Chemical Reactions: Change in color:

Example: Rusting of iron (silver-grey metal changes to reddish-brown).

Formation of a precipitate (solid):

Example: Mixing two clear solutions and a solid forms.

Evolution of a gas:

Example: Adding acid to limestone releases carbon dioxide gas.

Change in temperature:

Example: Burning wood releases heat (exothermic reaction).

Light production:

Example: Burning a candle produces light (and heat).

Types of Chemical Reactions: Combustion (Burning): A rapid reaction between a substance and oxygen, usually producing heat and light.