Science lesson plan · 11th grade (Year 12 in England) · 30 minutes
Atom economy and greener reactions
Chemical reactions, acids and bases
CCSS NGSS.HS-PS1-7CCSS NGSS.HS-ETS1-3England: GCSE Chemistry: Quantitative chemistry (atom economy)
Objective and success criteria
Students will: Atom economy and greener reactions.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Relative formula mass
Leads to: the next skill in this area.
Materials: Teacher demo or video, Indicator color chart, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).
Warm-up · 4 min
- Quick retrieval from earlier learning (Relative formula mass). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Calculate the relative formula mass (Mr) of H₂SO₄. Relative atomic masses: H = 1, S = 32, O = 16. → 98Prompt: Multiply each relative atomic mass by the number of those atoms.
- Calculate the relative formula mass (Mr) of calcium hydroxide, Ca(OH)₂. Relative atomic masses: Ca = 40, O = 16, H = 1. → 74Prompt: Count the atoms of each element first, including any brackets.
- What is the percentage by mass of carbon in CH₄? Relative atomic masses: C = 12, H = 1. Give 1 decimal place. → 75 %Prompt: Work out Mr first.
Hook · 3 min
- Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
- Share the objective: Atom economy and greener reactions. Read the success criteria together.
I do: model it · 7 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: CH₄ + H₂O → CO + 3H₂. The useful product is hydrogen (Mr 2). Relative masses of reactants: CH₄ = 16, H₂O = 18. What is the atom economy? Give 1 decimal place.
- Step 1: useful product: 6; reactants: 34
- Step 2: 6 ÷ 34 × 100 = 17.65
- Step 3: So the answer is: 17.6 %
- Answer: 17.6 %
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 6 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. The useful product is ethanol (Mr 46). Relative masses of reactants: C₆H₁₂O₆ = 180. What is the atom economy? Give 1 decimal place. → 51.1 %Prompt: atom economy = total Mr of the useful product ÷ total Mr of all reactants × 100
- Ethanol can be made by fermentation (atom economy 51 %) or by reacting ethene with steam (100 %). Why might a company still choose fermentation? (It is faster / It has a higher atom economy / It uses renewable sugar crops instead of crude oil / It produces purer ethanol) → It uses renewable sugar crops instead of crude oilPrompt: Where does ethene come from?
You do: independent practice · 7 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 6 questions are on the student sheet below, with answers in the key.
Exit ticket · 3 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Atom economy: which statement is NOT true? (Atom economy is the same as percentage yield. / Green chemistry aims to use reactions with high atom economy. / Reactions with only one product have 100 % atom economy. / Atom economy is calculated from the balanced equation.) → Atom economy is the same as percentage yield.Prompt: How is atom economy different from yield?
- CH₄ + H₂O → CO + 3H₂. The useful product is hydrogen (Mr 2). Relative masses of reactants: CH₄ = 16, H₂O = 18. What is the atom economy? Give 1 decimal place. → 17.6 %Prompt: atom economy = total Mr of the useful product ÷ total Mr of all reactants × 100
Watch out for
- Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
- Remembering facts without the reason: ask "why?" and "what is the evidence?"
Support and stretch
Support
- Review first: Relative formula mass.
- Use concrete materials: teacher demo or video.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-11.
Free lesson plan from eurekami.com/lesson-plan-builder