KASEMPA DAY SECONDARY
Grade/Class: Grade 11 Number of Pupils in Class: …………. Date: 2026-05-18 Duration: 80 minutes
Name of Teacher: MR MASUMBA D
Subject: Chemistry Topic: THE MOLE CONCEPT Subtopic: Relative masses Rationale: Understanding relative masses is fundamental to the Mole Concept, which is a cornerstone of quantitative chemistry. In the Zambian context, learners need a strong foundation in calculating relative atomic, molecular, and formula masses to engage with practical applications such as determining reactant quantities in industrial processes, understanding stoichiometry in agriculture (e.g., fertiliser composition), and interpreting chemical analyses relevant to mining and environmental science. This lesson will equip learners with essential mathematical calculation and formula manipulation skills. This is lesson number one in the THE MOLE CONCEPT study series, adopting a learner-centered approach through discussion, demonstration, and problem-solving methods to ensure active participation and conceptual understanding. Specific Outcome(s): By the end of the lesson, learners should be able to: • Describe Relative Atomic Mass and relative molecular mass. • Calculate the relative formula mass of a compound Prerequisite Knowledge: • Identification of elements and compounds using chemical symbols and formulae. • Basic understanding of atomic structure (protons, neutrons, electrons). • Ability to perform basic arithmetic operations (addition, multiplication). • Understanding of what an atom and a molecule are. References: • Zambian Chemistry Pupil's Textbook, Grade 11, pg. 140-143 Knowledge: RAM as relative mass of an element's isotopes as compared to carbon-12; RMM as relative mass of a molecule as compared to carbon-12; As the sum of the relative atomic masses of all the atoms in the compound Skills: Mathematical calculations; Formula manipulation; Data interpretation Values: Accuracy; Logical reasoning; Systematic problem-solving Teaching / Learning Aids: 1. Manila chart 1: "Relative Masses Definitions". This chart contains three sections. Section 1 is titled "RELATIVE ATOMIC MASS (RAM)" with the definition: "The average mass of an atom of an element compared to 112 the mass of one atom of carbon-12." Section 2 is titled "RELATIVE MOLECULAR MASS (RMM)" with the definition: "The sum of the relative atomic masses of all atoms in a molecule, compared to 112 the mass of one atom of carbon-12." Section 3 is titled "RELATIVE FORMULA MASS (RFM)" with the definition: "The sum of the relative atomic masses of all atoms in the formula unit of a compound, compared to 112 the mass of one atom of carbon-12." 2. Manila chart 2: "Table of Relative Atomic Masses". This chart has two columns. Column 1 heading: "Element". Column 2 heading: "Relative Atomic Mass (RAM)". The rows list: Hydrogen (H) - 1, Carbon (C) - 12, Oxygen (O) - 16, Sodium (Na) - 23, Sulphur (S) - 32, Chlorine (Cl) - 35.5, Potassium (K) - 39, Calcium (Ca) - 40, Iron (Fe) - 56. 3. Manila chart 3: "Worked Examples of RFM". This chart is titled "CALCULATING RELATIVE FORMULA MASS (RFM)". It displays Example 1: Water (H2O) with calculation steps: RAM of H = 1, RAM of O = 16. RFM(H2O) = (2 × 1) + (1 × 16) = 2 + 16 = 18. Example 2: Carbon Dioxide (CO2) with calculation steps: RAM of C = 12, RAM of O = 16. RFM(CO2) = (1 × 12) + (2 × 16) = 12 + 32 = 44. Alternative Materials: Whiteboard drawings, projected slides of charts, printed handouts of definitions and RAM table. METHODOLOGIES, STRATEGIES AND APPROACHES: Approach: Learner-Centered Approach Method: • Question & Answer Method — Introduction, Step 4 • Demonstration Method — Development Step 1 • Discussion Method — Step 2 • Problem Solving Method — Step 3 Strategy: • Guided Questioning — Introduction, Development Step 1, Step 2, Step 4 • Use of Charts/Diagrams — Development Step 1, Step 2, Step 3 • Group Work — Step 3 • Note-taking — Development Step 1, Step 2, Step 4 • Brainstorming — Introduction, Step 2 Lesson Implementation: [TABLE_START] Stage|Teaching Methods|Teacher's Activities|Learner's Activities|Learning Points Introduction - 10 min|Question & Answer Method|Teacher greets learners. Asks: "What is an atom?", "What is a molecule?", "What is a compound?" Displays the lesson topic and subtopic on the whiteboard. Asks: "Based on the subtopic 'Relative masses', what do you think we will be learning about today?"|Learners respond: "An atom is the smallest unit of an element.", "A molecule is two or more atoms chemically bonded together.", "A compound is a substance formed when two or more elements are chemically combined." Learners brainstorm ideas related to comparing masses of elements or compounds.|An atom is the smallest particle of an element. A molecule is formed when two or more atoms bond together. A compound is formed when two or more different elements bond chemically. The lesson will cover comparing the masses of atoms and compounds. Development Step 1 - 20 min|Demonstration Method|Teacher displays Manila chart 1, points to the three sections titled RELATIVE ATOMIC MASS (RAM), RELATIVE MOLECULAR MASS (RMM), and RELATIVE FORMULA MASS (RFM), and explains each definition, emphasizing comparison to 1/12 the mass of one atom of carbon-12. On the whiteboard, teacher shows that RAM is for an atom of an element, RMM is for a molecule, and RFM is for a formula unit of a compound.|Learners observe Manila chart 1, listen to the explanation, and state the three sections as RAM, RMM, and RFM. They copy each definition from the chart and note that all three are compared to 1/12 the mass of one atom of carbon-12. They also note that RAM is for an atom, RMM is for a molecule, and RFM is for a formula unit of a compound.|Relative Atomic Mass (RAM) is the average mass of an atom of an element compared to 112 the mass of one atom of carbon-12. Relative Molecular Mass (RMM) is the sum of the relative atomic masses of all atoms in a molecule, compared to 112 the mass of one atom of carbon-12. Relative Formula Mass (RFM) is the sum of the relative atomic masses of all atoms in the formula unit of a compound, compared to 112 the mass of one atom of carbon-12. Step 2 - 15 min|Discussion Method|Teacher displays Manila chart 2 and directs learners to the column headings Element and Relative Atomic Mass (RAM). Teacher asks learners to identify from the chart the RAM of Hydrogen (H) and Oxygen (O), then asks how these values are used to calculate the mass of water, H2O. Teacher then displays Manila chart 3 and explains both worked examples shown: Water (H2O) and Carbon Dioxide (CO2), showing that RFM is the sum of all RAMs in the formula.|Learners read the headings Element and Relative Atomic Mass (RAM) on Manila chart 2 and identify Hydrogen (H) as 1 and Oxygen (O) as 16. They answer that for H2O, the values are added as (2 × 1) + 16. They then observe Manila chart 3 and take notes on both worked examples: H2O = 18 and CO2 = 44.|The Relative Formula Mass (RFM) of a compound is calculated by summing the relative atomic masses (RAMs) of all the atoms present in its chemical formula. For example, to calculate the RFM of H2O: RFM(H2O) = (2 × RAM of H) + (1 × RAM of O) = (2 × 1) + (1 × 16) = 2 + 16 = 18. Step 3 - 20 min|Problem Solving Method|Teacher divides the class into groups of 5 and writes the formulae NaCl, H2SO4, and CaCO3 on the whiteboard. Teacher instructs learners to use Manila chart 2 to find the RAM values needed for each formula and calculate the RFM for all three compounds. Teacher moves round the groups, guiding learners where necessary.|Learners work in groups and use Manila chart 2 to find the RAM values for Na, Cl, H, S, O, Ca, and C. They calculate all three RFMs: NaCl = 23 + 35.5 = 58.5, H2SO4 = (2 × 1) + 32 + (4 × 16) = 98, and CaCO3 = 40 + 12 + (3 × 16) = 100. They record their working and answers.|Problem Set: Calculate the Relative Formula Mass (RFM) for the following compounds, using the RAM values provided on Manila chart 2:1. Sodium Chloride (NaCl)
2. Sulphuric Acid (H2SO4)
3. Calcium Carbonate (CaCO3)
Formula for RFM: Σ(number of atoms × RAM). Step 4 - 15 min|Question & Answer Method|Teacher invites groups to present their calculated RFM values. Facilitates a class discussion to compare answers and correct any misconceptions. Provides the correct solutions. Asks: "Why is it important to calculate relative masses in chemistry?" Assigns homework: "Calculate the RFM for Mg(OH)2 and C6H12O6. Use RAM values from Manila chart 2."|Groups present their RFM calculations for NaCl, H2SO4, and CaCO3. Learners engage in discussion, asking questions and clarifying understanding. They record the correct solutions. Learners respond that calculating relative masses is important for understanding chemical reactions, balancing equations, and determining quantities of substances. Learners copy the homework assignment.|Correct Solutions: 1. RFM(NaCl) = 23 + 35.5 = 58.5. 2. RFM(H2SO4) = (2 × 1) + (1 × 32) + (4 × 16) = 2 + 32 + 64 = 98. 3. RFM(CaCO3) = 40 + 12 + (3 × 16) = 40 + 12 + 48 = 100. Calculating relative masses is crucial for quantitative chemistry and stoichiometry. Homework: Calculate the RFM for Mg(OH)2 and C6H12O6. [TABLE_END] Lesson Evaluation: .......................................................................................................................................................................................................................................................... .......................................................................................................................................................................................................................................................... .......................................................................................................................................................................................................................................................... .......................................................................................................................................................................................................................................................... .......................................................................................................................................................................................................................................................... ..........................................................................................................................................................................................................................................................