ChemistryChapter 18: Qualitative Analysis
Hydrogen
Lab hydrogen: dilute H2SO4 + Zn -> ZnSO4 + H2.
Learning objectives
- State the main idea of hydrogen in clear words.
- Explain why hydrogen is useful in chemistry.
- Apply the correct method, observation, equation, or comparison.
- Avoid the common mistakes and write a complete exam answer.
Definition
Lab hydrogen: dilute H2SO4 + Zn -> ZnSO4 + H2. Collect it inverted (it is less dense than air). A burning splint gives a POP. The reaction is 2H2 + O2 -> 2H2O. This is not the glowing splint test. The first portion can mix with air, so test with caution.
Important terms
- dilute H2SO4
- Lab hydrogen: dilute H2SO4 + Zn -> ZnSO4 + H2.
- Zn
- Lab hydrogen: dilute H2SO4 + Zn -> ZnSO4 + H2.
- ZnSO4 + H2
- Lab hydrogen: dilute H2SO4 + Zn -> ZnSO4 + H2.
- inverted
- Lab hydrogen: dilute H2SO4 + Zn -> ZnSO4 + H2.
- less dense
- Lab hydrogen: dilute H2SO4 + Zn -> ZnSO4 + H2.
- burning splint
- Lab hydrogen: dilute H2SO4 + Zn -> ZnSO4 + H2.
Overview
Collect it, then light it with care:
Making and Collecting
Zinc and dilute sulfuric acid make hydrogen. Because H2 is less dense, hold the tube inverted or collect over water. Let the first bubbles pass if you can: they often carry air, and an air mix can bang harder.
Examples Zn + dilute H2SO4 · Tube held upside down · Discard the first portion
The Pop Test
Bring a burning splint to the mouth of the tube. A squeaky POP means hydrogen. A glowing splint is the oxygen test, not this one. The chemistry of the pop is 2H2 + O2 -> 2H2O (a small explosion).
Examples Burning splint: POP · Glowing splint: wrong test · H2 burns to water
WHAT — Core idea
Lab hydrogen: dilute H2SO4 + Zn -> ZnSO4 + H2. Collect it inverted (it is less dense than air). A burning splint gives a POP. The reaction is 2H2 + O2 -> 2H2O. This is not the glowing splint test. The first portion can mix with air, so test with caution.
WHY — Why it matters
If a gas burns more vigorously without a pop, think oxygen, not hydrogen. Hydrogen pops. Oxygen relights.
HOW — Method, evidence, or comparison
1. 1. MAKING AND COLLECTING: Zinc and dilute sulfuric acid make hydrogen. Because H2 is less dense, hold the tube inverted or collect over water. Let the first bubbles pass if you can: they often carry air, and an air mix can bang harder. 2. 2. THE POP TEST: Bring a burning splint to the mouth of the tube. A squeaky POP means hydrogen. A glowing splint is the oxygen test, not this one. The chemistry of the pop is 2H2 + O2 -> 2H2O (a small explosion).
HOW — Answer in an exam
Hydrogen: burning splint, POP, collect inverted. Oxygen: glowing splint, relights. Mix them up and the whole gas question falls.
Explanation
If a gas burns more vigorously without a pop, think oxygen, not hydrogen. Hydrogen pops. Oxygen relights.
In simple words
Hydrogen: burning splint, POP, collect inverted. Oxygen: glowing splint, relights. Mix them up and the whole gas question falls.
Key points
- dilute H2SO4
- Zn
- ZnSO4 + H2
- inverted
- Zinc
- less dense
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Hydrogen
Sticky Notes · Quick Revision
WHAT
- Lab hydrogen: dilute H2SO4 + Zn -> ZnSO4 + H2.
Key Points
- dilute H2SO4
- Zn
- ZnSO4 + H2
- inverted
- less dense
HOW
- Zinc and dilute sulfuric acid make hydrogen.
- Bring a burning splint to the mouth of the tube.
Example
- Zn + dilute H2SO4
- Tube held upside down
- Discard the first portion
Common Mistake
- Use a burning splint for hydrogen, not a glowing splint.
Exam Tip
- Hydrogen: burning splint, POP, collect inverted.
- Oxygen: glowing splint, relights.
60-second revision
- Lab hydrogen: dilute H2SO4 + Zn -> ZnSO4 + H2.
- Collect it inverted (it is less dense than air).
- Zinc and dilute sulfuric acid make hydrogen.
- Bring a burning splint to the mouth of the tube.
- Hydrogen: burning splint, POP, collect inverted.
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