ChemistryChapter 18: Qualitative Analysis
Oxygen
Oxygen supports combustion.
Learning objectives
- State the main idea of oxygen in clear words.
- Explain why oxygen is useful in chemistry.
- Apply the correct method, observation, equation, or comparison.
- Avoid the common mistakes and write a complete exam answer.
Definition
Oxygen supports combustion. A glowing splint relights in O2. In the lab it often comes from H2O2 decomposition (with a catalyst such as MnO2). A gas that makes a flame burn more vigorously without a pop is oxygen, not hydrogen.
Important terms
- supports combustion
- Oxygen supports combustion.
- glowing splint relights
- Oxygen supports combustion.
- H2O2
- Oxygen supports combustion.
- decomposition
- Oxygen supports combustion.
- more vigorously
- Oxygen supports combustion.
- without a pop
- Oxygen supports combustion.
Overview
The test and a common mix-up:
The Glowing Splint
Light a splint, blow it out so the tip still glows, then put it in the gas. If it relights, the gas is oxygen. The same gas will not milk limewater, so you can tell it from CO2.
Examples Glowing splint relights · Limewater stays clear · H2O2 -> O2 + H2O
Oxygen vs Hydrogen
Hydrogen pops with a burning splint. Oxygen relights a glowing splint and can make a flame burn more vigorously without a pop. Use the matching splint: burning for H2, glowing for O2.
Examples H2: POP · O2: relights · Stronger flame, no pop: O2
WHAT — Core idea
Oxygen supports combustion. A glowing splint relights in O2. In the lab it often comes from H2O2 decomposition (with a catalyst such as MnO2). A gas that makes a flame burn more vigorously without a pop is oxygen, not hydrogen.
WHY — Why it matters
SO2 is a different gas: acidified potassium manganate(VII) goes from purple to colourless. Do not use a splint test for SO2. Splints are for H2 and O2; limewater is for CO2; litmus stories are for ammonia and chlorine.
HOW — Method, evidence, or comparison
1. 1. THE GLOWING SPLINT: Light a splint, blow it out so the tip still glows, then put it in the gas. If it relights, the gas is oxygen. The same gas will not milk limewater, so you can tell it from CO2. 2. 2. OXYGEN VS HYDROGEN: Hydrogen pops with a burning splint. Oxygen relights a glowing splint and can make a flame burn more vigorously without a pop. Use the matching splint: burning for H2, glowing for O2.
HOW — Answer in an exam
Glowing splint relights = oxygen. Burning splint pops = hydrogen. Burning more vigorously without pop still points to oxygen.
Explanation
SO2 is a different gas: acidified potassium manganate(VII) goes from purple to colourless. Do not use a splint test for SO2. Splints are for H2 and O2; limewater is for CO2; litmus stories are for ammonia and chlorine.
In simple words
Glowing splint relights = oxygen. Burning splint pops = hydrogen. Burning more vigorously without pop still points to oxygen.
Key points
- supports combustion
- glowing splint relights
- H2O2
- decomposition
- glows
- relights
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Oxygen
Sticky Notes · Quick Revision
WHAT
- Oxygen supports combustion.
Key Points
- supports combustion
- glowing splint relights
- H2O2
- decomposition
- more vigorously
HOW
- Light a splint, blow it out so the tip still glows, then put it in the gas.
- Hydrogen pops with a burning splint.
Example
- Glowing splint relights
- Limewater stays clear
- H2O2 -> O2 + H2O
Common Mistake
- Oxygen relights a glowing splint; hydrogen gives a pop with a burning splint.
Exam Tip
- Glowing splint relights = oxygen.
- Burning splint pops = hydrogen.
60-second revision
- Oxygen supports combustion.
- A glowing splint relights in O2.
- Light a splint, blow it out so the tip still glows, then put it in the gas.
- Hydrogen pops with a burning splint.
- Glowing splint relights = oxygen.
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