Science lesson plan · 7th grade (Year 8 in England) · 45 minutes
Acids, alkalis (bases) and the pH scale
Chemical reactions, acids and bases
CCSS NGSS.MS-PS1-2England: KS3 Chemistry: Chemical reactions (acids and alkalis)
Objective and success criteria
Students will: Acids, alkalis (bases) and the pH scale.
- 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: Physical and chemical changes
Leads to: Neutralisation and naming salts; Read indicator colours to find pH; What acids make with metals and carbonates
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 (Physical and chemical changes). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Is this a physical or a chemical change: baking bread? (physical change / chemical change) → chemical changePrompt: Is a new substance made?
- A nail left outside turns orange-brown and flaky. What has happened? (Paint fell on it / Iron reacted with oxygen and water to make rust / The nail dissolved / The nail melted) → Iron reacted with oxygen and water to make rustPrompt: Rusting needs both air and water.
- Physical and chemical changes: which statement is NOT true? (All bubbles mean a chemical reaction. / Dissolving is a physical change. / Rusting needs both oxygen and water. / In a chemical reaction, atoms are rearranged to make new substances.) → All bubbles mean a chemical reaction.Prompt: Does each change make a new substance?
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: Acids, alkalis (bases) and the pH scale. 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: Universal indicator turns red in a solution. What does this tell you?
- Step 1: Red means pH about 0–2: strongly acidic. Green is neutral; purple is strongly alkaline.
- Step 2: So the answer is: It is a strong acid
- Answer: It is a strong acid
- 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.
- Which of these is an acid? (oven cleaner / soap / pure water / lemon juice) → lemon juicePrompt: Acids often taste sour (never taste chemicals in the lab!).
- Acids and alkalis: which statement is NOT true? (A pH of 1 is a weak acid. / Strong acids and alkalis can be corrosive, so eye protection is needed. / Pure water has a pH of 7. / Acids have a pH below 7.) → A pH of 1 is a weak acid.Prompt: Lower pH means more acidic.
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.
- Acids and alkalis: which statement is NOT true? (Acids have a pH below 7. / Alkalis are bases that dissolve in water. / All acids are dangerous. / Pure water has a pH of 7.) → All acids are dangerous.Prompt: Lower pH means more acidic.
- What happens to blue litmus paper in an acid? (It turns purple / It turns red / It stays blue / It turns green) → It turns redPrompt: Litmus has only two colours.
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: Physical and chemical changes.
- 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
- Move on to: Neutralisation and naming salts; Read indicator colours to find pH; What acids make with metals and carbonates.
- 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-7.
Free lesson plan from eurekami.com/lesson-plan-builder