Science lesson plan · 12th grade (Year 13 in England) · 45 minutes
pH and hydrogen ion concentration
Chemical reactions, acids and bases
CCSS NGSS.HS-PS1-6England: GCSE Chemistry: Chemical changes (strong and weak acids, Higher)
Objective and success criteria
Students will: pH and hydrogen ion concentration.
- 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: Read indicator colours to find pH
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 (Read indicator colours to find pH). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- A solution has a pH of 12. What colour will universal indicator turn? (purple / green / blue / orange or yellow) → purplePrompt: Universal indicator runs like a rainbow from strong acid to strong alkali.
- A pH meter is better than universal indicator when… (you want a rainbow of colours / the solution is colourless / you are testing a solid / you need a precise numerical pH) → you need a precise numerical pHPrompt: Colours have to be judged by eye.
- Universal indicator results: milk pH 6, oven cleaner pH 13, vinegar pH 3, soapy water pH 10. Which is the most alkaline? (milk / vinegar / oven cleaner / soapy water) → oven cleanerPrompt: The lower the pH, the more acidic.
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: pH and hydrogen ion concentration. 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: Solution X has pH 5 and solution Y has pH 7. How many times greater is the hydrogen ion concentration in X than in Y?
- Step 1: 10^2 = 100
- Step 2: So the answer is: 100
- Answer: 100
- 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.
- Solution X has pH 4 and solution Y has pH 5. How many times greater is the hydrogen ion concentration in X than in Y? → 10Prompt: Each drop of 1 pH unit means 10 times more H⁺ ions.
- A strong acid solution has a hydrogen ion concentration of 0.1 mol/dm³. What is its pH? (pH = −log₁₀[H⁺]) → 1Prompt: Write the concentration as a power of ten.
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.
- Solution X has pH 5 and solution Y has pH 6. How many times greater is the hydrogen ion concentration in X than in Y? → 10Prompt: Each drop of 1 pH unit means 10 times more H⁺ ions.
- A strong acid is diluted so its H⁺ concentration becomes 10 times smaller. What happens to its pH? (it rises by 1 / it does not change / it rises by 10 / it falls by 1) → it rises by 1Prompt: pH is a logarithmic scale.
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: Read indicator colours to find pH.
- 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