Lesson Notes By Weeks and Term v4 - SHS 3
EQUILIBRIA
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EQUILIBRIA
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Subject: Chemistry
Class: SHS 3
Term: 2nd Term
Week: 4
Grade code: 1.1.1.LI.3
Strand code: 1
Sub-strand code: 2
Content standard code: 1.1.2.CS.1
Indicator code: 1.1.1.LI.3
Theme: PHYSICAL CHEMISTRY
Subtheme: EQUILIBRIA
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Good day, future scientists and engineers! Today, we are diving into a very practical and important aspect of chemistry called Qualitative Analysis. Think of it as chemical detective work. In our daily lives in Ghana, we are surrounded by chemical compounds. How do we know if our borehole water is safe to drink and free from harmful ions like lead from 'galamsey' activities? How does the Food and Drugs Authority (FDA) check that the correct active ingredient is in a medicine? The answer lies in identifying the specific ions present in a substance.
This lesson is built on one central idea: selective precipitation. We add a specific chemical (a reagent) to our unknown solution, which will react with only certain ions to form an insoluble solid called a precipitate. The colour of this precipitate, and whether it dissolves in excess reagent, gives us clues to the ion's identity. Part 1: The Foundation - Solubility Rules
Before we can do any tests, we must know which compounds are generally soluble or insoluble in water. These are not absolute laws, but very reliable guidelines.
General Solubility Rules for Ionic Compounds in Water:
| Soluble Compounds | Exceptions (These are Insoluble) | | :--- | :--- | | All Nitrates (NO₃⁻) | None | | All salts of Group 1 metals (Li⁺, Na⁺, K⁺) | None | | All Ammonium (NH₄⁺) salts | None | | All Chlorides (Cl⁻), Bromides (Br⁻), and Iodides (I⁻) | Salts of Silver (Ag⁺), Lead(II) (Pb²⁺), and Mercury(I) (Hg₂²⁺). *(Note: PbCl₂ is slightly soluble in hot water)* | | All Sulfates (SO₄²⁻) | Salts of Barium (Ba²⁺), Strontium (Sr²⁺), Lead(II) (Pb²⁺), and Calcium (Ca²⁺). |