Lesson 4a — Chemical Analysis

Gas Tests I: H₂ · O₂ · CO₂

Spec: 2.44

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🌍 Did you know? In 1937 the Hindenburg airship exploded because it was filled with hydrogen — the "squeaky pop" test detects that same gas.

Learning Objective:

2.44 – Describe tests for hydrogen, oxygen and carbon dioxide (ammonia & chlorine next lesson).

🏆 Success Criteria — I will…

…name the correct test for H₂, O₂ and CO₂.
…state what I would observe (the positive result).
…write an observation → conclusion sentence.

Navigation: Arrow Keys / Spacebar | 40 minutes | TA Focus & Cold Call top-left

🖨️ Pupil Packs

Arrival Task

Arrival Task – Recall from Lesson 3

Welcome back! It's been a while, so just have a go — use the 💡 hints and the word bank if you're stuck. Q1–3 are a quick warm-up; Q4 leads into today.
🧠 "Burns with a Bang" = Burning splint → H₂ squeaky pop. "Glows and Goes" = Glowing splint → O₂ relights.

1. Acids

Acids release one of these ions. Tap the correct one:

H⁺OH⁻Na⁺

H is for Hydrogen — acids are full of H⁺ ions.

H⁺ (hydrogen ions).

2. Base or Alkali?

True or false?
"An alkali is a base that dissolves in water."

TrueFalse

All alkalis are bases — but only the bases that dissolve in water are called alkalis.

True — an alkali is a soluble base (it dissolves in water and releases OH⁻ ions).

3. Neutralisation

Fill the gaps using the word bank:
Acid + Base → ______ + ______

An acid and a base react to make a salt and one very common liquid.

Acid + Base → Salt + Water.

4. Today's Lead-in 🔬

Today we learn how to test gases. Name ONE piece of equipment a scientist might use to test a gas.

Think about a wooden splint, limewater, or litmus paper.

Any one of: a (burning or glowing) splint, limewater, damp litmus paper, a delivery tube.

🧰 Word bank: H⁺ · OH⁻ · base · alkali · salt · water · splint · limewater · litmus paper

Starter – Predict Like a Scientist

Starter: Predict the Tests! 🔮 (5 mins)

No marks — no wrong answers yet. Scientists predict first, then test. For each gas, tap the test you THINK identifies it. We check the first THREE this lesson — your NH₃ and Cl₂ predictions get tested NEXT lesson. (Your table sheet gets filled in during the lesson — no copying today.)

H₂ Hydrogen🔥 Burning splint✨ Glowing splint🧴 Limewater📄 Damp litmus

O₂ Oxygen🔥 Burning splint✨ Glowing splint🧴 Limewater📄 Damp litmus

CO₂ Carbon dioxide🔥 Burning splint✨ Glowing splint🧴 Limewater📄 Damp litmus

NH₃ Ammonia🔥 Burning splint✨ Glowing splint🧴 Limewater📄 Damp litmus

Cl₂ Chlorine🔥 Burning splint✨ Glowing splint🧴 Limewater📄 Damp litmus

Predictions made: 0/5

🌟 Extension: Tell your partner WHY you picked each one. A reason is what makes a prediction scientific.

Six taps, sixty seconds — quick recall from Lessons 1–3. Tap, lock, move on.

1. Acids release which ion?

H⁺OH⁻Na⁺

2. Red litmus in an ALKALI turns…

BlueStays redWhite

3. Acid + Base → ?

Salt + waterSalt + hydrogenWater only

4. Universal indicator in STRONG acid?

RedGreenPurple

5. Mg + HCl gives off which gas?

H₂O₂CO₂

6. Neutral pH is…

7114

🌟 Finished? Q5 is a clue about TODAY — which test would prove that gas is hydrogen?

Which is the odd one out — and WHY? Any answer with a reason scores. Talk first, then reveal.

H₂ HydrogenO₂ OxygenCO₂ Carbon dioxide🧴 Limewater

All defensible: Limewater — the only TEST (the rest are gases) · CO₂ — the only gas tested with a liquid · O₂ — the only one that RELIGHTS a splint · H₂ — the only one that goes POP. The reason is the science.

🌟 Stretch: Invent your own odd-one-out set of four for a partner to solve.

I Do

I Do: Testing for H₂, O₂ and CO₂

🦉 OWL · OBSERVE

Fill in your table sheet as we go through each gas test. Watch carefully and name what you must notice (the positive result). 🔮 Prediction check: did you call these in the Starter?

H₂

Hydrogen

Test: hold a burning splint near the gas.

Result: a "squeaky pop".

The pop is the tiny explosion of H₂ + O₂ → H₂O.

O₂

Oxygen

Test: place a glowing splint into the gas.

Result: the splint relights.

Oxygen supports combustion — it makes things burn.

CO₂

Carbon Dioxide

Test: bubble through limewater (calcium hydroxide solution).

Result: turns milky / cloudy.

CO₂ + Ca(OH)₂ → insoluble CaCO₃ (the white cloudiness).

💡 Key Distinction: Burning splint = flame still lit (for H₂). Glowing splint = blown out so only the red ember remains (for O₂). Students often confuse these!

I Do 🦉 OWL · OBSERVE

Observe: Watch It For Real 👀

Run each lab station, then watch the REAL thing. Before each test: say the TEST, predict the OBSERVATION, then run it. Did your Starter prediction hold?

🧪 THE TESTING LAB — tap a station to run its test

Run A → B → C, or any order · results stay until reset

GCSE Science Chemistry (9-1) · Tests for Gases. If blocked on the school network, use the buttons.

▶ Hydrogen (pop) ↗ ▶ Oxygen (relight) ↗ ▶ Carbon dioxide ↗

👀 Say it as you watch: I see ___, so the gas is ___.

We Do

We Do: Gas Test Relay 🏃

As a class: the three gases we've learned so far (H₂, O₂, CO₂). Drag each gas onto the test that identifies it. Get it right and the result appears. 0/3 matched

Drag a gas up to its test — or tap a gas, then tap its test.

🧪 Hydrogen (H₂)

🧪 Oxygen (O₂)

🧪 Carbon dioxide (CO₂)

🔥 Burning splint

✨ Glowing splint

🧴 Limewater

Statement 1/6

👍 Thumbs-up / stand = TRUE · 👎 thumbs-down / stay sat = FALSE — everyone votes!

Tap the steps in the right order to build the exam method.

Independent Work – 8 mins

Independent Work

Answer independently. ❌ Never write just "splint" — always say BURNING splint or GLOWING splint.

Questions completed: 0/0

📗 Grades U–1 • Grade 2 challenge marked with ⭐

MCQ

1. How do you test for oxygen?

Oxygen relights a GLOWING splint — an ember, no flame.

Burning splintGlowing splintLimewater

MCQ

2. Hydrogen makes a:

Hydrogen ignites — a tiny explosion. What sound is that?

Squeaky popRelights splintTurns milky

Short

3. What does CO₂ do to limewater?

LIMEwater turns MILKY — cloudy, like milk.

Turns it milky/cloudy.

Short

4. Name the gas that turns limewater milky.

The gas in fizzy drinks.

Carbon dioxide (CO₂).

⭐ Exam [3 marks]

5. A student collects a gas. A burning splint at the tube mouth gives a squeaky pop. (a) Name the gas [1]. (b) State the test [1]. (c) Describe the positive result [1].

"Burns with a Bang" — which gas pops?

(a) The gas is ______. (b) The test: hold a ______ splint near the gas. (c) The result is a ______ ______.

(a) Hydrogen. (b) Hold a burning splint near the gas. (c) A squeaky pop.

🌟 Finished? Flip the toggle and try ONE Middle question — the limewater one is closer than you think.

📙 Grades 1–2 • Grade 3 challenge marked with ⭐

MCQ

1. A glowing splint relights. The gas is:

Only one gas relights a glowing splint — the one that supports burning.

H₂O₂CO₂

Short

2. Explain the difference between the H₂ and O₂ splint tests.

One has a FLAME (burning), one has an EMBER (glowing). Which gas for which?

H₂: burning splint (flame visible) → squeaky pop. O₂: glowing splint (ember only) → relights.

Short

3. Limewater is a solution of which substance?

Formula Ca(OH)₂ — calcium something.

Calcium hydroxide.

⭐ Exam [4 marks]

4. A student reacts Mg with HCl. A gas bubbles off. (a) Name the gas [1]. (b) Describe the test and result [2]. (c) Write a word equation [1].

Metal + acid makes the gas that goes "pop". Name it.

(a) Hydrogen. (b) Hold burning splint near gas – squeaky pop. (c) Magnesium + hydrochloric acid → magnesium chloride + hydrogen.

🌟 Finished? Try the Higher MCQ (Q1) — you already know why the pop happens.

📘 Grades 3–4 • Grade 5 challenge marked with ⭐

MCQ

1. A burning splint "pops" in hydrogen because:

Think 2H₂ + O₂ → 2H₂O.

H₂ ignites explosively with O₂, making waterH₂ is denser than airThe splint contains hydrogen

Short

2. Write the equation for CO₂ turning limewater milky.

CO₂ + calcium hydroxide → calcium carbonate (insoluble = milky) + water.

CO₂ + Ca(OH)₂ → CaCO₃ + H₂O. CaCO₃ is insoluble → white precipitate (milky).

Short

3. Write the equation for the squeaky pop test.

Hydrogen burns in oxygen to make water. Balance: 2H₂ + O₂ → 2H₂O.

2H₂ + O₂ → 2H₂O (hydrogen combustion).

⭐ Exam [6 marks]

4. A student has 3 test tubes: H₂, O₂, CO₂. She has a splint, matches, and limewater. Describe a systematic method to identify all three. For each step: test, observation, conclusion.

Glowing splint first (finds O₂), then burning splint (finds H₂), then limewater (confirms CO₂).

Step 1: Insert glowing splint into each. One relights → O₂ identified. Step 2: Hold burning splint at mouth of remaining two. One gives squeaky pop → H₂ identified. Step 3: Bubble remaining gas through limewater – turns milky → CO₂ confirmed.

🎯 Examiner wants: on the 6-marker, EACH gas needs Test → Observation → Conclusion. Three gases × 3 parts = the marks. Tick them off as you write.

🌟 Finished? Write your OWN exam question about these tests — with a mark scheme. Hardest thing in science: thinking like the examiner.

Exit Ticket – 3 mins

Exit Ticket

No notes. From memory only. Your tier question = one observation + one conclusion. Then everyone answers the safety/method check below.

✅ Method check (everyone): Name one safety precaution a scientist takes when testing gases.

1) How do you test for hydrogen?

Hold a burning splint near the gas. It makes a squeaky pop.

2) What does CO₂ do to limewater?

Turns it milky/cloudy.

3) A glowing splint relights — name the gas.

Oxygen.

Name: ________________________ Class: __________ Date: ____________

🎯 Learning Objective (2.44): Describe tests for hydrogen, oxygen and carbon dioxide (ammonia & chlorine next lesson).

🏆 Success Criteria — tick at the END of the lesson:

☐ I can name the correct test for H₂, O₂ and CO₂.

☐ I can state what I would observe (the positive result).

☐ I can write an observation → conclusion sentence.

Knowledge Organiser – Lesson 4a: Gas Tests I (H₂ · O₂ · CO₂)

Gas	Formula	Test	Positive Result
Hydrogen	H₂	Hold a burning splint near the gas	Squeaky pop
Oxygen	O₂	Place a glowing splint in the gas	Splint relights
Carbon dioxide	CO₂	Bubble through limewater	Turns milky / cloudy
Ammonia	NH₃	— Lesson 4b: you fill this in next lesson —
Chlorine	Cl₂	— Lesson 4b: you fill this in next lesson —

Key distinctions: Burning splint (flame visible) = H₂ test. Glowing splint (ember only) = O₂ test. If limewater stays CLEAR, the gas is NOT CO₂ — a negative result is still evidence.

🧠 Self-quiz routine (everyone): COVER the table → WRITE the tests from memory → CHECK → fix any gaps. Do it twice — the second go is where it sticks.

⚠️ Common mark-losers: writing just "splint" (say BURNING or GLOWING) · "calcium chloride" (limewater is calcium HYDROXIDE) · holding limewater NEAR the gas (it must be BUBBLED through) · mixing up which splint pops and which relights.

🎵 Memory hooks: "Burns with a Bang" = H₂ · "Glows and Goes back alight" = O₂ · "LIMEwater goes MILKY" = CO₂.

Arrival Task

1. Acids release one of these ions — circle it: H⁺ / OH⁻ / Na⁺

2. True or false? "An alkali is a base that dissolves in water." True / False

3. Fill the gaps: Acid + Base → ______ + ______

4. Lead-in: Today we test gases. Name ONE piece of equipment a scientist might use to test a gas.

🧰 Word bank: H⁺ · OH⁻ · base · alkali · salt · water · splint · limewater · litmus paper

Gas Test Table — fill in during the lesson

Stick this in your book. Fill in each row as we learn the test (no copying needed). Rows 4–5 get filled NEXT lesson.

Gas	Formula	Test	Positive Result
Hydrogen	H₂
Oxygen	O₂
Carbon dioxide	CO₂
Ammonia	NH₃
Chlorine	Cl₂

🔮 My Starter predictions I got right: ______ / 5

We Do: Gas Test Matching

Part 1: Draw a line to match each gas to its correct test and result.

Gas	Test	Positive Result
Hydrogen (H₂)
Oxygen (O₂)
Carbon dioxide (CO₂)

Part 2: A student performs these tests. Identify each gas.

Observation	Gas
Burning splint → squeaky pop
Glowing splint relights
Limewater turns milky
Limewater stays clear (no change)	NOT ___ (which gas is ruled out?)

Scaffolding Sheet

All Five Gas Tests

Gas	Test	Result	Memory Aid
H₂	Burning splint	Squeaky pop	H₂ goes "pop!" like a tiny explosion
O₂	Glowing splint	Relights	O₂ supports burning – it lights things up
CO₂	Bubble through limewater	Turns milky	LIMEwater goes MILKY
NH₃	— next lesson (4b) —
Cl₂	— next lesson (4b) —

Common Mistakes

• Don't confuse BURNING splint (H₂) with GLOWING splint (O₂).

• Limewater must have the gas BUBBLED through it — not just held near.

• Limewater staying CLEAR is evidence too: the gas is NOT CO₂. Say so!

📝 Word Bank (Foundation)

Use these words: hydrogen, oxygen, carbon dioxide, burning splint, glowing splint, limewater, squeaky pop, relights, milky, cloudy

✍️ Sentence Starters

• To test for ___, you use a...

• The positive result is...

• A burning splint is different from a glowing splint because...

• The gas is ___ because the test showed...

⭐ Exam frame: (a) The gas is ______. (b) The test: hold a ______ splint near the gas. (c) The result is a ______ ______.

📙 Explain-It Toolkit (Middle)

Key words you MUST use: burning · glowing · relights · squeaky pop · limewater · calcium hydroxide · milky

Explain stems: "The gas is ___ because…" · "This shows that…" · "The difference between the two splint tests is…"

Self-check: every answer = TEST + RESULT + GAS NAME. Missing one = missing marks.

Chemistry Behind the Tests (Higher)

• H₂: 2H₂ + O₂ → 2H₂O (explosive combustion → pop)

• O₂: supports combustion → relights glowing material

• CO₂ + Ca(OH)₂ → CaCO₃ + H₂O (CaCO₃ is insoluble → milky)

• CO₂ does not support combustion → a burning splint goes OUT (useful contrast with O₂)

• Litmus-pair chemistry (NH₃, Cl₂) → Lesson 4b

🎯 Command words: DESCRIBE = say what happens · EXPLAIN = say WHY (use "because") · COMPARE = similarities AND differences · PLAN/METHOD = numbered steps.

6-mark frame: for EACH gas — Step n: do the TEST → state the OBSERVATION → draw the CONCLUSION. Repeat per gas, add ONE safety point.

Independent Work – Foundation (Grades U–1)

Multiple Choice & Short Answer

1. How do you test for oxygen?

[ ] Burning splint [ ] Glowing splint [ ] Limewater

2. What result shows hydrogen is present?

[ ] Relights [ ] Squeaky pop [ ] Turns milky

3. What does CO₂ do to limewater?

4. What is the difference between a BURNING splint and a GLOWING splint?

Long Answer

5. Complete the table:

Gas	Test	Positive Result
Hydrogen
Oxygen
Carbon dioxide

6. A gas turns limewater milky. Name the gas.

Exam-Style Questions

7. [3 marks] A student collects a gas during a reaction. She holds a burning splint at the top of the test tube and hears a squeaky pop.

(a) Name the gas. [1 mark]

(b) State the test she used. [1 mark]

8. [3 marks] Describe how you would test a gas to show it is carbon dioxide. State the equipment needed, the method and the positive result.

Independent Work – Middle (Grades 1–2)

Multiple Choice & Short Answer

1. Why must you use a GLOWING splint (not burning) for oxygen?

2. Describe the positive test result for hydrogen AND for oxygen.

3. Why is the hydrogen test result described as a "squeaky pop"? What reaction is happening?

4. Name the substance limewater is a solution of.

Long Answer

5. A student tests four unknown gases. Identify each gas:

Observation	Gas
Glowing splint relights
Limewater turns milky
A burning splint at the mouth — loud squeaky pop

Exam-Style Questions

6. [4 marks] A student reacts zinc with hydrochloric acid. A gas is produced. (a) Name the gas likely produced. [1 mark]

(b) Describe the test and the expected result. [2 marks]

7. [4 marks] Compare the splint tests for hydrogen and oxygen. State what you would observe for each gas and explain why the splint must be BURNING for one test and GLOWING for the other.

Independent Work – Higher (Grades 3–4)

Multiple Choice & Short Answer

1. Write the equation for the reaction that occurs when CO₂ is bubbled through limewater.

2. Explain why the hydrogen test produces a "pop" — include the balanced symbol equation.

3. Suggest why a glowing splint relights in oxygen but a burning splint goes OUT in carbon dioxide.

Long Answer

4. A student performs the following reactions and collects the gases. For each, name the gas produced and describe how to confirm its identity:

Reaction	Gas Produced	Test & Result
Mg + HCl
CaCO₃ + HCl
Electrolysis of water (at cathode)
Electrolysis of water (at anode)

Exam-Style Questions

5. [5 marks] A student heats copper carbonate (CuCO₃) and collects the gas given off.

(a) Predict the gas produced. [1 mark]

(b) Describe the test and the expected positive result. [2 marks]

6. [6 marks] A student is given three test tubes, each containing an unknown gas: one is H₂, one is O₂, and one is CO₂. She has a wooden splint, matches, and limewater available. Describe a systematic method she could use to identify all three gases. For each step, state the test performed, the expected observation, and the conclusion drawn.

Exit Ticket – Foundation (U–1)

1) How do you test for hydrogen?

2) What does CO₂ do to limewater?

3) A glowing splint relights — name the gas.

Exit Ticket – Middle (1–2)

1) A glowing splint relights. Name the gas and explain why.

2) Describe how you would prove a gas is carbon dioxide.

3) Why is the splint test for H₂ different from the one for O₂?

Exit Ticket – Higher (3–4)

1) Explain the chemistry behind CO₂ turning limewater milky.

2) Why does a burning splint go OUT in CO₂ but a glowing splint relights in O₂?

3) Write the balanced equation for the squeaky pop and name the product.

Gas Tests I: H₂ · O₂ · CO₂

🖨️ Pupil Packs

Arrival Task – Recall from Lesson 3

1. Acids

2. Base or Alkali?

3. Neutralisation

4. Today's Lead-in 🔬

Starter: Predict the Tests! 🔮 (5 mins)

I Do: Testing for H₂, O₂ and CO₂

Hydrogen

Oxygen

Carbon Dioxide

Observe: Watch It For Real 👀

We Do: Gas Test Relay 🏃

Independent Work

Exit Ticket

Knowledge Organiser – Lesson 4a: Gas Tests I (H₂ · O₂ · CO₂)

Arrival Task

Gas Test Table — fill in during the lesson

We Do: Gas Test Matching

Scaffolding Sheet

All Five Gas Tests

Common Mistakes

📝 Word Bank (Foundation)

✍️ Sentence Starters

📙 Explain-It Toolkit (Middle)

Chemistry Behind the Tests (Higher)

Independent Work – Foundation (Grades U–1)

Multiple Choice & Short Answer

Long Answer

Exam-Style Questions

Independent Work – Middle (Grades 1–2)

Multiple Choice & Short Answer

Long Answer

Exam-Style Questions

Independent Work – Higher (Grades 3–4)

Multiple Choice & Short Answer

Long Answer

Exam-Style Questions

Exit Ticket – Foundation (U–1)

Exit Ticket – Middle (1–2)

Exit Ticket – Higher (3–4)

🧑‍🏫 TA Focus —

📋 Teacher Notes —

🎯 Cold Call

🎉 Lesson Complete!