Lesson Notes By Weeks and Term v4 - SHS 1
SCIENCE AND MATERIALS IN NATURE
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SCIENCE AND MATERIALS IN NATURE
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Subject: General Science
Class: SHS 1
Term: 2nd Term
Week: 7
Grade code: 3.1.1.LI.3
Strand code: 1
Sub-strand code: 1
Content standard code: 3.1.1.CS.1
Indicator code: 3.1.1.LI.3
Theme: EXPLORING MATERIALS
Subtheme: SCIENCE AND MATERIALS IN NATURE
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Oxygen is one of the most vital gases on Earth, making up about 21% of the air we breathe. Without it, life as we know it would not exist. From the oxygen cylinders in our major hospitals like Korle-Bu and Komfo Anokye Teaching Hospital to the local welder in Suame Magazine or Kokompe using an oxy-acetylene torch, understanding how to produce and use oxygen is fundamental to science and has direct applications in our communities. In this lesson, we will perform a hands-on activity to prepare oxygen in the laboratory, investigate its properties, and explore its numerous important uses in Ghana and beyond.
A. What is Oxygen? Oxygen is a chemical element with the symbol O. In nature, it commonly exists as a molecule made of two oxygen atoms bonded together, which we call dioxygen (O₂). It is a colourless, odourless, and tasteless gas that is essential for respiration in most living organisms and for combustion (burning). B. Laboratory Preparation of Oxygen While there are several ways to produce oxygen, the safest and most common method in a school laboratory is the catalytic decomposition of hydrogen peroxide. Principle: Hydrogen peroxide (H₂O₂) is a compound that naturally breaks down (decomposes) into water (H₂O) and oxygen (O₂). This process is usually very slow. To speed it up, we use a catalyst. Catalyst: A catalyst is a substance that increases the rate of a chemical reaction without being chemically changed or used up in the process. For this reaction, we use manganese(IV) oxide (MnO₂), a black powder, as the catalyst. Chemicals and Apparatus Required: Chemicals: Hydrogen peroxide solution (H₂O₂) Manganese(IV) oxide (MnO₂ - the catalyst) Water Apparatus: Conical flask (or flat-bottomed flask) Thistle funnel Delivery tube Water trough (or large bowl) Beehive shelf Gas jars (for collecting the gas) Spatula Wooden splint and matches The Reaction Equation: The overall chemical reaction is: 2H₂O₂(aq) ---[MnO₂ catalyst]---> 2H₂O(l) + O₂(g) `2H₂O₂(aq)` means two molecules of hydrogen peroxide dissolved in water (aqueous solution). `2H₂O(l)` means two molecules of liquid water are produced. `O₂(g)` means one molecule of oxygen gas is produced. The `MnO₂` is written over the arrow to show it is a catalyst and not a reactant. C. Procedure for Preparation and Collection
Step 1: Setting up the Apparatus Arrange the apparatus as shown in the diagram below. Place the beehive shelf inside the water trough and fill the trough with water until the shelf is covered. Fill a gas jar completely with water, cover its mouth with a glass plate, invert it, and place it over the hole in the beehive shelf. Remove the glass plate once the jar is underwater. Put about two spatulas of manganese(IV) oxide powder into the conical flask. Fit the thistle funnel and the delivery tube into the flask using a two-holed rubber stopper. Ensure the tip of the thistle funnel is below the level where the hydrogen peroxide will be. Place the other end of the delivery tube under the inverted gas jar in the water trough.
*(Teacher should draw this diagram on the board)*
Step 2: Generating the Gas Carefully pour hydrogen peroxide solution through the thistle funnel into the conical flask. You will immediately see bubbles of gas (effervescence) being produced in the flask. Allow the first few bubbles that come through the delivery tube to escape, as this is just the air being pushed out of the flask.