Science · Practical

🧪 🥽 🧴

Making Limewater

The solution we’ll use to test for carbon dioxide — today we make it and leave it to stand.

Today I will…

Recall how we test for the three gases
Explain what limewater is and why it goes milky with CO₂
Safely make and label a batch to test next lesson

Success criteria: I can name the CO₂ test · I can state 3 safety musts · I make & label my limewater

Arrival · Recall

Which test shows carbon dioxide?

Tap the test that means the gas is carbon dioxide.

🔥 Squeaky “pop” with a burning splint

✨ Relights a glowing splint

🧴 Turns limewater cloudy / milky

💧 Turns damp litmus red

Gas	Test	Result
Hydrogen (H₂)	Burning splint	Squeaky “pop”
Oxygen (O₂)	Glowing splint	Relights
Carbon dioxide (CO₂)	Bubble through limewater	Goes cloudy / milky

Stuck? Think of our Gas Tests lesson — which liquid went milky? That’s the one we’re making today.

Starter · Safety

Safety first — spot the musts

Limewater is made from calcium hydroxide — an irritant. It can sting skin, eyes and airways, and we’re using glassware.

Talk task: what are the 3 safety musts for today? Tell the person next to you.

1. Goggles on — the whole time we’re at the bench.

2. Only the dilute solution — I handle the powder, you handle the finished liquid.

3. Mind the glass, wash your hands — and tell me about any spill (we rinse with water).

~~It’s just water, so it’s fine.~~ — no: calcium hydroxide is alkaline and irritant, so goggles stay on.

I Do · What is limewater?

What limewater is — and why it goes milky

Limewater is a solution of calcium hydroxide, Ca(OH)₂, dissolved in water. We make it so we can test for carbon dioxide.

It turns cloudy / milky — a white solid (calcium carbonate) forms and hangs in the liquid.

Word: calcium hydroxide + carbon dioxide → calcium carbonate + water

Symbol: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Exam tip: cloudy = CO₂ is present. Staying clear is a result too — it means the gas is not CO₂.

We Do · The method

Let’s put the method in order — together

Which step comes next? Tap the steps into the right order — green locks in; a wrong tap just wobbles, so try another.

✅ Method sorted! Now let’s make it — grab your bench card and go.

🌟 Aspire: why does old limewater sometimes stay clear even with CO₂? (It’s already reacted with carbon dioxide in the air.)

Independent · Make it

Your turn — make your limewater 🦉

Foundation

Middle

Higher

On the bench: beaker · ~500 ml water · calcium hydroxide (from me) · stirrer · label + pen · goggles.

Foundation. Follow the steps, make your limewater, and label it.

“I made limewater and labelled it ______.”

🌟 Finished? Draw what you think it will look like next lesson.

Middle. Make and label it, then write what it will show next lesson and why.

“Next lesson it will go ______ because ______, which shows the gas is ______.”

🌟 Finished? Explain why we leave it to stand.

Higher. Make and label it, then write the word and symbol equation for limewater + CO₂.

Word: ______ + ______ → ______ + ______
Symbol: Ca(OH)₂ + CO₂ → ______ + ______

Exam tip: name the observation (milky) and the product (calcium carbonate) for full marks.

🌟 Finished? Suggest how you’d check your limewater still works next lesson.

Conclusion & Exit

Show what you know

Foundation

Middle

Higher

Exit · Foundation: Which gas turns limewater milky?

Exit · Middle: What will you see next lesson, and what does it tell you?

Exit · Higher: Write the word (and symbol) equation for limewater + carbon dioxide.

🗣️ Say the conclusion, then close the loop (teacher-led — the class says it aloud at their depth; you confirm the model live)

🟩 BUILD — say it aloud, then tap to confirm

Limewater is calcium hydroxide dissolved in water. It goes cloudy when carbon dioxide is bubbled through.

🟧 GROW — say it aloud, then tap to confirm

…because a white solid (calcium carbonate) forms. That’s how we test for carbon dioxide.

🟦 LAUNCH — say it aloud, then tap to confirm

calcium hydroxide + carbon dioxide → calcium carbonate + water · Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. Old limewater can stay clear because it’s already reacted with CO₂ in the air.

🟡 Yellow Box — live next step (tap to push a pupil up a level)

🔁 Feedback loop no loops opened yet

Per pupil: mark made & labelled, then close the loop ◻ → 🟡 VF given → 🟢 R (responded).

📷 Snap each pupil’s finished, labelled limewater on their row (📷 button) before it goes to stand — it prints on their sheet.