ChemistryChapter 18: Qualitative Analysis
Chlorine
Chlorine bleaches. Damp blue litmus goes red, THEN bleaches white.
Learning objectives
- State the main idea of chlorine in clear words.
- Explain why chlorine is useful in chemistry.
- Apply the correct method, observation, equation, or comparison.
- Avoid the common mistakes and write a complete exam answer.
Definition
Chlorine bleaches. Damp blue litmus goes red, THEN bleaches white. Damp is needed so the gas can dissolve and act. If you have only seen red so far, continue watching: the bleach is the part that names chlorine, not the red alone.
Important terms
- damp blue litmus
- Chlorine bleaches.
- red
- Chlorine bleaches.
- THEN bleaches white
- Chlorine bleaches.
- Damp
- Chlorine bleaches.
- continue watching
- Chlorine bleaches.
Overview
The colour change has two stages:
The Test
Use damp blue litmus. Acidic chlorine solution turns it red first. Then bleaching takes the colour all the way to white. A gas that only reddens litmus and stops there is not confirmed as chlorine.
Examples Blue -> red -> white · Stop at red: not enough · Dry paper: weak or no change
Uses
Chlorine is used as a bleach and as a disinfectant (kills microbes in water). Those uses match the lab test: it destroys coloured dyes and living cells. Handle it with care; it is toxic.
Examples Bleaching cloth · Treating drinking water · Pool disinfection
WHAT — Core idea
Chlorine bleaches. Damp blue litmus goes red, THEN bleaches white. Damp is needed so the gas can dissolve and act. If you have only seen red so far, continue watching: the bleach is the part that names chlorine, not the red alone.
WHY — Why it matters
Red then white is the full story. Hydrogen chloride would redden damp litmus but would not bleach it white. Watch until the paper is white, or say the test is incomplete.
HOW — Method, evidence, or comparison
1. 1. THE TEST: Use damp blue litmus. Acidic chlorine solution turns it red first. Then bleaching takes the colour all the way to white. A gas that only reddens litmus and stops there is not confirmed as chlorine. 2. 2. USES: Chlorine is used as a bleach and as a disinfectant (kills microbes in water). Those uses match the lab test: it destroys coloured dyes and living cells. Handle it with care; it is toxic.
HOW — Answer in an exam
Damp blue litmus: red THEN white. If the answer only says "turns red," it could be any acidic gas. The bleach is the chlorine signature.
Explanation
Red then white is the full story. Hydrogen chloride would redden damp litmus but would not bleach it white. Watch until the paper is white, or say the test is incomplete.
In simple words
Damp blue litmus: red THEN white. If the answer only says "turns red," it could be any acidic gas. The bleach is the chlorine signature.
Key points
- damp blue litmus
- red
- THEN bleaches white
- Damp
- red first
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Chlorine
Sticky Notes · Quick Revision
WHAT
- Chlorine bleaches.
Key Points
- damp blue litmus
- red
- THEN bleaches white
- Damp
- continue watching
HOW
- Use damp blue litmus.
- Chlorine is used as a bleach and as a disinfectant (kills microbes in water).
Example
- Blue -> red -> white
- Stop at red: not enough
- Dry paper: weak or no change
Common Mistake
- Chlorine changes damp blue litmus red and then white; red alone is not confirmation.
Exam Tip
- Damp blue litmus: red THEN white.
- If the answer only says "turns red," it could be any acidic gas.
60-second revision
- Chlorine bleaches.
- Damp blue litmus goes red, THEN bleaches white.
- Use damp blue litmus.
- Chlorine is used as a bleach and as a disinfectant (kills microbes in water).
- Damp blue litmus: red THEN white.
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