ChemistryChapter 12: Halogens
Halide Tests (named)
School halide test: acidify with dilute HNO₃, add AgNO₃.
Learning objectives
- Explain Halide Tests (named) using Group 17 language.
- Link trends to size, shielding, forces and bond strength.
- Apply equations and observations in FBISE-style answers.
Definition
School halide test: acidify with dilute HNO₃, add AgNO₃. Precipitates: AgCl white, AgBr cream, AgI yellow. Solubility in ammonia helps confirm: AgCl dissolves in dilute NH₃, AgBr in concentrated NH₃, AgI remains insoluble. These are precipitate colours — not elemental halogen colours.
Core Concept
AgCl white · AgBr cream · AgI yellow Acidify (dilute HNO₃) → add AgNO₃ → observe ppt → test with NH₃. AgCl soluble in dilute NH₃; AgBr in conc. NH₃; AgI insoluble. F⁻: no AgF ppt (soluble) in the school story.
Beginner
Add acid, then silver nitrate. White ppt = chloride; cream = bromide; yellow = iodide. Ammonia: white dissolves easily, cream needs concentrated ammonia, yellow stays.
Intermediate
Always acidify first. Quote AgCl/AgBr/AgI colours exactly. Use NH₃ ladder for confirmation. Never swap elemental Br₂ red-brown with AgBr cream.
Advanced
Acidification removes interfering anions that also precipitate with Ag⁺. Ammonia works by forming soluble silver–ammine complexes for AgCl and (with concentrated NH₃) AgBr; AgI’s lattice/low solubility keeps it out of solution in the school model.
Remember
AgCl white · AgBr cream · AgI yellow · dilute NH₃ dissolves AgCl · conc NH₃ dissolves AgBr · AgI stays · NOT elemental colours.
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Halide Tests (named)
Sticky Notes · Quick Revision
Precipitate colours
- AgCl white
- AgBr cream
- AgI yellow
Method
- Acidify (HNO₃)
- Add AgNO₃
- Then NH₃
NH₃ ladder
- AgCl — dilute NH₃
- AgBr — conc NH₃
- AgI — insoluble
Not the same as
- Cl₂ greenish-yellow
- Br₂ red-brown
- I₂ violet vapour
60-second revision
- AgCl white, AgBr cream, AgI yellow after acidified AgNO₃.
- NH₃: AgCl dilute, AgBr concentrated, AgI stays.
- These are ppt colours, not elemental halogen colours.
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