Lesson Notes By Weeks and Term v4 - SHS 3
MATTER AND ITS PROPERTIES
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
MATTER AND ITS PROPERTIES
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Chemistry
Class: SHS 3
Term: 2nd Term
Week: 3
Grade code: 1.1.1.LI.6
Strand code: 1
Sub-strand code: 1
Content standard code: 1.1.1.CS.3
Indicator code: 1.1.1.LI.6
Theme: PHYSICAL CHEMISTRY
Subtheme: MATTER AND ITS PROPERTIES
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.
This lesson focuses on the practical preparation and identification of three common and important gases: Hydrogen (H₂), Carbon (IV) Oxide (CO₂), and Ammonia (NH₃). While we know that matter exists as solids, liquids, and gases, understanding how to produce and identify specific gases is a fundamental skill in chemistry. These gases are not just abstract concepts; they are vital to our daily lives in Ghana. The fizz in our FanYogo and Coca-Cola is CO₂, the fertilizers used by our cocoa farmers depend on ammonia, and hydrogen is being explored as a clean fuel for the future.
This section is divided into three parts, one for each gas. For each gas, we will explore its properties, preparation, collection, and identification. A. HYDROGEN GAS (H₂) Properties of Hydrogen Physical Properties: Colourless and odourless gas. It is the lightest known substance and is much less dense than air. Insoluble in water. Chemical Properties: Burns in air with a pale blue flame to form water (2H₂(g) + O₂(g) → 2H₂O(l)). It is a powerful reducing agent. A mixture of hydrogen and air/oxygen is explosive. Laboratory Preparation of Hydrogen Principle: Hydrogen is prepared by the action of a moderately reactive metal (above hydrogen in the reactivity series, e.g., Zinc, Magnesium) with a dilute non-oxidising acid (e.g., HCl or H₂SO₄). Reactants: Zinc granules (Zn) and dilute Hydrochloric acid (HCl). *Note:* We use zinc granules instead of powder to ensure a moderate, controllable reaction rate. Concentrated acids are not used as they can produce other unwanted gases. Chemical Equation: ``` Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g) ``` Apparatus: Flat-bottomed flask (or Kipp's apparatus), thistle funnel, delivery tube, trough, beehive shelf, gas jar. Procedure: Place a few zinc granules in the flat-bottomed flask. Set up the apparatus as shown in the diagram below. Ensure the thistle funnel dips below the level of the acid to be added, to prevent the gas from escaping through it. Add dilute hydrochloric acid through the thistle funnel to cover the zinc granules. Effervescence (fizzing) occurs immediately, and hydrogen gas is produced. Allow the first few bubbles to escape as this will be a mixture of air and hydrogen. Collect the gas over water in an inverted gas jar. Collection Method: Over water: This is the preferred method because hydrogen is insoluble in water. Upward delivery / Downward displacement of air: This method can also be used because hydrogen is much less dense than air. The gas jar is held upside down to be filled. Confirmatory Test: Place a lit splint at the mouth of the test tube or gas jar containing the gas. Observation: The flame goes out with a loud 'pop' sound. This is the definitive test for hydrogen.
Diagram for Hydrogen Preparation: *(Teacher should draw this on the board, or provide a chart)* A flat-bottomed flask containing zinc granules. A thistle funnel extends into the flask, its tip below the acid level. A delivery tube leads from the side arm of the flask, under a beehive shelf in a trough of water. An inverted gas jar filled with water is placed over the beehive shelf to collect the gas.
B. CARBON (IV) OXIDE GAS (CO₂) Properties of Carbon (IV) Oxide Physical Properties: A colourless and odourless gas. About 1.5 times denser than air. Slightly soluble in water to form a weakly acidic solution (carbonic acid, H₂CO₃). Chemical Properties: It does not burn and does not support combustion (hence its use in fire extinguishers). It is an acidic gas and will turn moist blue litmus paper faintly red. Reacts with alkalis (like calcium hydroxide) to form insoluble carbonates. Laboratory Preparation of Carbon (IV) Oxide Principle: Prepared by the action of a dilute acid on a metallic carbonate. Reactants: Calcium carbonate (CaCO₃) in the form of marble chips and dilute Hydrochloric acid (HCl). *Note:* Dilute H₂SO₄ is not suitable because it forms insoluble calcium sulphate (CaSO₄), which coats the marble chips and stops the reaction. Chemical Equation: ``` CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g) ``` Apparatus: Flat-bottomed flask (or Kipp's apparatus), thistle funnel, delivery tube, gas jar. Procedure: Place some marble chips into the flat-bottomed flask. Set up the apparatus. The thistle funnel must dip below the acid level. Add dilute HCl through the thistle funnel. A brisk effervescence occurs, producing carbon (IV) oxide gas. The gas is then passed through a delivery tube into an upright gas jar. Collection Method: Downward delivery / Upward displacement of air: This method is used because CO₂ is denser than air. The gas sinks and fills the jar from the bottom up, pushing the lighter air out. It cannot be effectively collected over water because it is slightly soluble. Confirmatory Test: Bubble the gas through a test tube containing limewater (a saturated solution of calcium hydroxide, Ca(OH)₂). Observation: The clear, colourless limewater turns milky or cloudy due to the formation of a white precipitate of insoluble calcium carbonate. Equation for the test: ``` Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l) ``` *Note:* If you bubble excess CO₂ through, the milkiness disappears as soluble calcium hydrogencarbonate is formed.
Diagram for CO₂ Preparation: *(Teacher to draw)* Similar setup to hydrogen, but the delivery tube leads directly into an UPRIGHT gas jar. No water trough is needed.