Science lesson plan · 12th grade (Year 13 in England) · 45 minutes
Find the limiting reactant and how much product forms
Chemical reactions, acids and bases
CCSS NGSS.HS-PS1-7England: GCSE Chemistry: Quantitative chemistry (limiting reactants, Higher)
Objective and success criteria
Students will: Find the limiting reactant and how much product forms.
- 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: Moles and reacting masses; Percentage yield
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 · 5 min
- Quick retrieval from earlier learning (Moles and reacting masses; Percentage yield). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- How many moles are in 11.7 g of sodium chloride (NaCl, Mr = 58.5)? → 0.2 molPrompt: moles = mass ÷ Mr
- A reaction could make 25 g of product in theory, but 21.25 g was actually collected. What is the percentage yield? → 85 %Prompt: percentage yield = actual mass ÷ theoretical mass × 100
- What is the mass of 2 mol of sodium chloride (NaCl, Mr = 58.5), in g? → 117 gPrompt: mass = moles × Mr
Hook · 5 min
- Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
- Share the objective: Find the limiting reactant and how much product forms. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: CH₄ + 2O₂ → CO₂ + 2H₂O. 1 mol of methane is mixed with 1 mol of oxygen. Which is the limiting reactant?
- Step 1: methane: 1 ÷ 1 = 1; oxygen: 1 ÷ 2 = 0.5
- Step 2: So the answer is: oxygen
- Answer: oxygen
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- N₂ + 3H₂ → 2NH₃. 2 mol of nitrogen is mixed with 3 mol of hydrogen. Which is the limiting reactant? (nitrogen / hydrogen) → hydrogenPrompt: Divide each amount by its number in the equation.
- Mg + 2HCl → MgCl₂ + H₂. 1 mol of magnesium reacts with 3 mol of hydrochloric acid. What is the maximum amount of hydrogen that can form, in mol? Give 2 decimal places if needed. → 1 molPrompt: Find the limiting reactant first.
You do: independent practice · 10 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 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- N₂ + 3H₂ → 2NH₃. 3 mol of nitrogen reacts with 4 mol of hydrogen. What is the maximum amount of ammonia that can form, in mol? Give 2 decimal places if needed. → 2.67 molPrompt: Find the limiting reactant first.
- In a car engine with too little air, which reactant is limiting and what is the risk? (oxygen is limiting, so incomplete combustion makes carbon monoxide / nitrogen is limiting, so no reaction happens / nothing is limiting / fuel is limiting, so too much oxygen forms) → oxygen is limiting, so incomplete combustion makes carbon monoxidePrompt: Which reactant runs out first?
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: Moles and reacting masses.
- 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-12.
Free lesson plan from eurekami.com/lesson-plan-builder