ChemistryChapter 18: Qualitative Analysis
Tests For Aqueous Ions (overview)
Besides gases and flames, school qualitative analysis uses precipitates.
Definition
Besides gases and flames, school qualitative analysis uses precipitates. Sodium hydroxide and ammonia are common reagents for cations. Silver nitrate (with dilute nitric acid first) for halides. Barium chloride (with HCl) for sulphate. These are identity tests, not amounts.
Overview
Two reagent families:
Cations With Alkali
Cu2+: blue ppt with NaOH, does not dissolve in excess NaOH (does in excess NH3 in the usual table). Fe2+: green ppt. Fe3+: brown ppt. Ca2+: white ppt, insoluble in excess NaOH. Learn the book's table; colours must match it.
Examples Clean tubes · Add slowly, then excess · Not a drain-cleaner experiment
Anions
Cl-: white ppt with AgNO3, dissolves in dilute NH3. Br-: cream. I-: yellow. SO4 2-: white ppt with BaCl2, insoluble in acid. CO3 2-: acid -> CO2 that turns limewater milky (gas page).
Examples Acidify before AgNO3 as taught · Distinguish sulphate from sulphite if the book does · Do not mix unknown leftover chemicals
Explanation
A confirmatory test is a second, different observation. Sodium's yellow flame can hide potassium: use blue glass as on the flame-test page.
In simple words
Precipitate colour in a dirty tube is worthless. Qualitative analysis is as much cleanliness as memory.
Key points
- precipitate colours
- NaOH and NH3
- AgNO3 and BaCl2
- blue Cu
- brown Fe3+
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Tests For Aqueous Ions (overview)
Sticky Notes · Quick Revision
Core Idea
- Besides gases and flames, school qualitative analysis uses precipitates.
Key Points
- precipitate colours
- NaOH and NH3
- AgNO3 and BaCl2
Simple Check
- Explain tests for aqueous ions (overview) in your own words and connect it to one chapter example.
How to Answer
- Define the idea, show the main rule or evidence, apply it, and check the final statement.
Common Mistake
- Precipitate colour in a dirty tube is worthless. Qualitative analysis is as much cleanliness as memory.
FBISE Exam Tip
- Use the exact term, show working where needed, and include units or labelled evidence.
60-second revision
- precipitate colours
- NaOH and NH3
- AgNO3 and BaCl2
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