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: 6
Grade code: 3.1.1.LI.2
Strand code: 1
Sub-strand code: 1
Content standard code: 3.1.1.CS.1
Indicator code: 3.1.1.LI.2
Theme: EXPLORING MATERIALS
Subtheme: SCIENCE AND MATERIALS IN NATURE
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Welcome, students! Today, we are going to explore a gas that is all around us and inside us. It's the gas that plants "breathe in" to give us food, the fizz in your favourite bottle of Coca-Cola or Malta Guinness, and the gas we breathe out with every breath. This gas is Carbon Dioxide (CO₂) . Understanding how to prepare it in the lab and knowing its properties helps us appreciate its vital role in nature, industry, and even in our own kitchens. From baking bread to putting out fires, CO₂ is a silent but powerful worker in our world.
This section will provide all the necessary information to understand the preparation, properties, and uses of Carbon Dioxide (CO₂). A. What is Carbon Dioxide? Chemical Formula: CO₂ Composition: It is a compound made of one Carbon (C) atom covalently bonded to two Oxygen (O) atoms. Occurrence: It is naturally present in the Earth's atmosphere (about 0.04%), released during respiration (breathing out), decay of organic matter, and combustion (burning). B. Laboratory Preparation of Carbon Dioxide
The most common and reliable method for preparing CO₂ in a school laboratory is by reacting a carbonate with a dilute acid. General Principle: `Acid + Metal Carbonate → Salt + Water + Carbon Dioxide` Specific Reactants Used: Calcium Carbonate (CaCO₃): This is easily found in the form of marble chips. Other sources like powdered eggshells or limestone can also be used. Dilute Hydrochloric Acid (HCl): This acid is preferred because the salt it produces, Calcium Chloride (CaCl₂), is soluble in water and does not form a layer on the marble chips that would stop the reaction. (Note: Dilute Sulphuric Acid is not suitable because it forms insoluble Calcium Sulphate (CaSO₄), which coats the marble and stops the reaction.) Apparatus: Flat-bottomed flask (or a Woulfe's bottle) Thistle funnel Delivery tube Gas jar and cover Retort stand and clamp (for support) Diagram of the Setup: *(Imagine a diagram showing a flat-bottomed flask on a bench. Marble chips are inside. A thistle funnel goes through the cork into the flask, its tip below the level where the acid will be. A delivery tube also goes through the cork, leading out and into an upright gas jar.)* Procedure (Step-by-step): Place a few marble chips (calcium carbonate) into the flat-bottomed flask. Set up the apparatus as shown in the diagram, ensuring the thistle funnel's tip is below the level of the acid that will be added. This is crucial to prevent the gas from escaping through the funnel. Pour dilute hydrochloric acid through the thistle funnel into the flask to cover the marble chips. You will immediately observe effervescence (fizzing or bubbling) as carbon dioxide gas is produced. The gas passes through the delivery tube and is collected in the gas jar. Method of Collection: Upward Displacement of Air (or Downward Delivery) The delivery tube is placed at the bottom of an *upright* gas jar. The CO₂ gas, being denser than air, sinks to the bottom of the jar and gradually fills it up, pushing the lighter air out from the top. The jar is full when a lit splint placed at the mouth of the jar goes out. Chemical Equation for the Reaction: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g) Reactants: CaCO₃(s) - Solid Calcium Carbonate 2HCl(aq) - Aqueous Hydrochloric Acid Products: CaCl₂(aq) - Aqueous Calcium Chloride (a salt) H₂O(l) - Liquid Water CO₂(g) - Gaseous Carbon Dioxide C. Test for Carbon Dioxide
To confirm that the gas produced is indeed CO₂, we use the Limewater Test. Procedure: Bubble the gas through limewater, which is a saturated solution of calcium hydroxide, Ca(OH)₂. Observation: The clear, colourless limewater turns milky or chalky. Explanation: The CO₂ reacts with the calcium hydroxide to form a white, insoluble precipitate of calcium carbonate (the same substance as marble chips!). Chemical Equation for the Test: Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l) D. Properties of Carbon Dioxide
Physical Properties: It is a colourless and odourless gas. It has a slightly sour taste when dissolved in water because it forms weak carbonic acid. It is about 1.5 times denser than air. This is why it can be collected by upward displacement of air. It is slightly soluble in water.