Science lesson plan · 12th grade (Year 13 in England) · 60 minutes
Dilution calculations (c₁V₁ = c₂V₂)
Chemical reactions, acids and bases
CCSS NGSS.HS-PS1-7England: A level Chemistry: Amount of substance (extension)
Objective and success criteria
Students will: Dilution calculations (c₁V₁ = c₂V₂).
- 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: Concentration in mol/dm³
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 · 6 min
- Quick retrieval from earlier learning (Concentration in mol/dm³). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- 0.025 mol of hydrochloric acid is in 100 cm³ of solution. What is the concentration, in mol/dm³? → 0.25 mol/dm³Prompt: concentration = moles ÷ volume in dm³
- How many moles of sodium hydroxide are in 25 cm³ of a 0.1 mol/dm³ solution? → 0.0025 molPrompt: moles = concentration × volume in dm³
- What mass of sodium chloride (NaCl, Mr = 58.5) is needed to make 250 cm³ of 0.1 mol/dm³ solution, in g? Give 2 decimal places. → 1.46 gPrompt: Find the moles needed first.
Hook · 6 min
- Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
- Share the objective: Dilution calculations (c₁V₁ = c₂V₂). Read the success criteria together.
I do: model it · 12 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: 10 cm³ of 1 mol/dm³ acid is diluted with water to a total volume of 20 cm³. What is the new concentration, in mol/dm³?
- Step 1: 1 × 10 ÷ 20 = 0.5
- Step 2: So the answer is: 0.5 mol/dm³
- Answer: 0.5 mol/dm³
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 12 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- 50 cm³ of 0.5 mol/dm³ acid is diluted with water to a total volume of 200 cm³. What is the new concentration, in mol/dm³? → 0.125 mol/dm³Prompt: The moles of acid do not change when water is added.
- What volume of 1 mol/dm³ stock solution is needed to make 250 cm³ of 0.5 mol/dm³ solution, in cm³? → 125 cm³Prompt: V₁ = c₂ × V₂ ÷ c₁
You do: independent practice · 17 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 · 7 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- 25 cm³ of 0.5 mol/dm³ acid is diluted with water to a total volume of 250 cm³. What is the new concentration, in mol/dm³? → 0.05 mol/dm³Prompt: The moles of acid do not change when water is added.
- 10 cm³ of a solution is diluted 20 times (its concentration becomes 1/20 of the original). How much water must be added, in cm³? → 190 cm³Prompt: Find the final total volume 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: Concentration in mol/dm³.
- 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