Curriculum
Chemistry
Chapter 1 - Transition Elements and Iron Metallurgy
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1.1Where they are in the periodic table1.2The main transition elements (d-block)1.3The four transition series1.4Economic importance of the first-series elements1.5Electron configurations of the first series1.6Rules for filling1.7Configurations of the common ions1.8Why Fe(II) is easily oxidized to Fe(III) but Mn(II) is not1.9Oxidation-state rules for the series1.10Calculating oxidation states in compounds1.11Definition of a transition element
Chapter 2 - Chemical Analysis
0/221.1Revision of concepts and laws needed in this chapter1.2Importance1.3Kinds of analysis1.4Qualitative analysis1.5A. Identification of acid radicals (anions)1.6(1) Dilute hydrochloric acid group1.7(2) Concentrated sulphuric acid group1.8(3) Barium chloride group1.9Practical differentiation between pairs of salts (typical exam type)1.10Reasoning questions1.11Detailed Comparison Matrix: Diagnostic Silver Nitrate (AgNO3) Confirmatory Matrix
Chapter 3 - Chemical Equilibrium
0/221.1The equilibrium system1.2Types of chemical reactions1.3Chemical equilibrium1.4Rate of reaction1.5Factors affecting the rate of a reaction1.6Nature of the reactants1.7Concentration and the law of mass action1.8Temperature — collision theory1.9Pressure1.10Le Chatelier's principle1.11Catalysts1.12Light
2.1Strong and weak electrolytes2.2Hydronium ion2.3Definitions2.4Ostwald's dilution law2.5Hydronium ion concentration of a weak acid2.6Hydroxide ion concentration of a weak base2.7Ionization of water and the ionic product Kw2.8pH and pOH2.9Solubility and solubility product2.10Summary of key relations
Chapter 4 - Electrochemistry
0/331.1The starting experiment: zinc in copper sulphate1.2The idea behind the galvanic cell1.3Construction of the Daniell cell1.4What happens at each electrode1.5When does the current stop?1.6The salt bridge — what it is and why it is needed1.7Why we need a reference1.8The standard hydrogen electrode1.9Standard electrode potentials1.10Measuring an electrode potential (idea of the experiment)1.11Definition1.12What the series tells us (the conclusions to know)1.13Calculating the cell emf1.14Cell notation (cell diagram)
3.1The electrolytic cell3.2Example: electrolysis of copper(II) chloride solution3.3First law3.4Second law3.5The faraday3.6The working formula3.7Worked examples3.8Electroplating3.9Extraction of aluminium3.10Electrorefining of copper3.11Galvanic cells versus electrolytic cells3.12Scientists and the value of electrochemistry
Chapter 5 - Organic Chemistry
0/721.1Historical background1.2Modern definition1.3Why are there so many organic compounds?1.4Comparison: organic and inorganic compounds1.5Molecular formula1.6Structural formula1.7Isomerism1.8Detecting carbon and hydrogen in an organic compound1.9Classification of hydrocarbons1.10Structure and the homologous series1.11Alkyl radicals (R–)1.12IUPAC nomenclature of alkanes1.13Methane — occurrence and preparation1.14Physical properties1.15Chemical properties of alkanes
5.1Functional groups5.2Alcohols and phenols — the difference5.3Nomenclature of alcohols5.4Classification of alcohols5.5Ethanol — preparation5.6Denatured (methylated) alcohol — "red spirit"5.7Physical properties5.8Chemical properties of ethanol5.9Uses of alcohols5.10Phenols5.11Preparation5.12Physical properties5.13Chemical properties5.14Tests for phenol
6.1The carboxyl group6.2Types6.3Nomenclature6.4Preparation of acetic acid6.5Physical properties6.6Chemical properties6.7Aromatic acids: benzoic acid6.8Important acids and their uses6.9Definition and formation6.10Nomenclature6.11Preparation6.12Physical properties6.13Chemical properties6.14Applications of esters6.15Aspirin6.16Types of organic reactions (summary)6.17Revision key points for Part B
7.1The birth of organic chemistry and the vital-force theory7.2Why organic compounds are so abundant7.3Organic versus inorganic compounds7.4Molecular formula, structural formula and isomers7.5Detecting carbon and hydrogen in an organic compound7.6Hydrocarbons and the alkane series7.7The alkyl radical and IUPAC naming7.8Methane, physical and chemical properties of alkanes7.9Practice with answers7.10Ministry exam traps
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Text lesson
Lesson 2: Qualitative Analysis of Basic Radicals (Cations)
Lesson 2: Qualitative Analysis of Basic Radicals (Cations)
Overview
Overview
🌳 Concept tree
- Qualitative Analysis of Basic Radicals (Cations)
- ├── B. Identification of basic radicals (cations)
- └── Identifying an unknown (worked reasoning)
Lesson 2: Qualitative Analysis of Basic Radicals (Cations) · 1 / 4
B. Identification of basic radicals (cations)
B. Identification of basic radicals (cations)
- This is harder than anion analysis because there are many cations, they interfere with each other, and one metal may have several oxidation states.
- Cations are divided into six analytical groups, each with its group reagent.
- The classification depends on the different solubilities of their salts.
- For example, the first group (Ag+, Hg₂2+, Pb2+) chlorides are sparingly soluble in water and are precipitated as chlorides by the group reagent, dilute HCl.
- A usual summary of the six groups (for orientation only; you are examined on the examples below):
| Group | Group reagent | Precipitate | Examples |
|---|---|---|---|
| 1 | dilute HCl | chlorides | Ag+, Hg₂2+, Pb2+ |
| 2 | H₂S in acidic medium | sulphides | Cu2+, Cd2+, Bi3+ |
| 3 | NH₄OH | hydroxides | Al3+, Fe2+, Fe3+ |
| 4 | H₂S in alkaline medium | sulphides | Zn2+, Ni2+, Co2+, Mn2+ |
| 5 | (NH₄)₂CO₃ | carbonates | Ca2+, Sr2+, Ba2+ |
| 6 | no common group reagent | — | Mg2+, Na+, K+, NH₄+ |
- We study examples from several groups.
- Second analytical group — example Cu2+. Precipitated as sulphides in acidic medium: dissolve the salt in water, acidify with dilute HCl and pass H₂S.
- CuSO₄ + H₂S → H₂SO₄ + CuS↓ (black copper(II) sulphide, soluble in hot nitric acid: 3CuS + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 3S + 4H₂O).
Third analytical group — Al3+, Fe2+, Fe3+.→Precipitated as hydroxides by ammonium hydroxide (group reagent) when no other interfering cations are present.
| Cation | NH₄OH | NaOH (confirmatory) |
|---|---|---|
| Al3+ | White gelatinous ppt. Al(OH)₃: Al₂(SO₄)₃ + 6NH₄OH → 3(NH₄)₂SO₄ + 2Al(OH)₃↓ (soluble in dil. acids and in caustic soda) | White gelatinous ppt. that dissolves in excess NaOH giving sodium meta-aluminate: Al₂(SO₄)₃ + 6NaOH → 3Na₂SO₄ + 2Al(OH)₃↓; Al(OH)₃ + NaOH → NaAlO₂ + 2H₂O |
| Fe2+ |
|
White-green ppt. of Fe(OH)₂: FeSO₄ + 2NaOH → Na₂SO₄ + Fe(OH)₂↓ |
| Fe3+ | Reddish-brown gelatinous ppt.: FeCl₃ + 3NH₄OH → 3NH₄Cl + Fe(OH)₃↓ (soluble in acids) | Reddish-brown ppt.: FeCl₃ + 3NaOH → 3NaCl + Fe(OH)₃↓ |
Fifth analytical group — example Ca2+.→Precipitated as carbonates by ammonium carbonate (group reagent).
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| • |
| CaCl₂₂CO₃2NH₄ClCaCO₃ |
| Confirmatory | dilute H₂SO₄ gives a white ppt. of CaSO₄: CaCl₂ + H₂SO₄ → 2HCl + CaSO₄↓ | diluteH₂SO₄giveswhite |
| Flame test | calcium salts colour the Bunsen flame brick red | calciumsaltscolourBunsen |
Lesson 2: Qualitative Analysis of Basic Radicals (Cations) · 2 / 4
Identifying an unknown (worked reasoning)
Identifying an unknown (worked reasoning)
✍️ Worked examples
- Example 3.1.
- A solid white salt X, with dilute HCl, gives a colourless gas with an irritating smell that turns acidified dichromate paper green; with AgNO₃ solution X gives a white precipitate that turns black on heating.
- Conclusion the anion is sulphite, SO₃2−.
- Example 3.2.
- A salt solution gives a reddish-brown gelatinous precipitate with NaOH and with NH₄OH, insoluble in excess.
- The cation is Fe3+.
- If the precipitate had been white and dissolved in excess NaOH, it would be Al3+; if white-green turning brown in air, Fe2+.
- Example 3.3. Hydrochloric acid is added to three solid sodium salts: (1) a colourless gas that turns reddish brown at the mouth of the tube is NO from nitrite; (2) a gas with an irritating smell and a yellow turbidity is SO₂ and S from thiosulphate; (3) a gas that turns lime water milky and a white precipitate with MgSO₄ in the cold means carbonate.
Lesson 2: Qualitative Analysis of Basic Radicals (Cations) · 3 / 4
Part 4
Part 4
- 📖
🔍 In-Depth Explanations, Deductions & Multi-Book Insights:
Chemistry Thanaweya Amma (2026/2027)
- Lesson 2 – Qualitative Analysis of Basic Radicals (Cations)
- Detailed Academic Lesson Overview:
- Cation detection is more intricate than anion detection due to the vast multiplicity of basic radicals and their multiple oxidation states.
- Cations are divided into six analytical groups depending on the solubility of their precipitates.
🌳 Hierarchy Classification & Conceptual Roadmap
Analytical Groups of Cations
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| ├── Group I (Reagent | Dilute HCl) | Dilute |
| • | │ └── Ag+, Pb2+, Hg+ precipitated as insoluble Chlorides (AgCl, PbCl2, Hg2Cl2) | precipitatedinsolubleChloridesAgCl |
| ├── Group II (Reagent | H2S in acidic medium HCl) | acidicmedium |
| • | │ └── Cu2+ precipitated as black Copper(II) sulfide (CuS) | precipitatedblackCoppersulfide |
| ├── Group III (Reagent | Ammonium hydroxide NH4OH in presence of NH4Cl) | AmmoniumhydroxideNH4OHpresence |
| │ ├── Fe2+ |
| Dirtywhiteturninggreen |
| │ ├── Fe3+ | Reddish-brown gelatinous ppt of Fe(OH)3 insoluble in excess NaOH | Reddishbrowngelatinousinsoluble |
| │ └── Al3+ | White gelatinous ppt of Al(OH)3 soluble in excess NaOH forming Sodium Meta-aluminate | Whitegelatinoussolubleexcess |
| └── Group V (Reagent | Ammonium carbonate (NH4)2CO3) | Ammoniumcarbonate2CO3 |
| • | └── Ca2+ precipitated as white Calcium carbonate (CaCO3); gives brick-red flame test | precipitatedwhiteCalciumcarbonate |
| • | 📋 Master Teacher's Blackboard Rules & Exam Secrets | MasterTeacherBlackboardRules |
| RULE 1 |
| GroupreagentNH4OHamphoteric |
| RULE 2 | Ca2+ dry flame test gives a distinct characteristic brick-red coloration to the non-luminous Bunsen burner flame | flametestgivesdistinct |
| RULE 3 | Group II precipitation requires an acidic medium (dil. HCl) so that only CuS precipitates without precipitating Group III or IV sulfides | Groupprecipitationrequiresacidic |
| 📊 Detailed Comparison Matrix | Separation and Confirmatory Reactions for Group III Cations | SeparationConfirmatoryReactionsGroup |
| Cation | Precipitate with NH4OH | Effect of Excess NaOH | Confirmatory Characteristic |
|---|---|---|---|
| Al3+ | White gelatinous Al(OH)3 | Dissolves forming soluble NaAlO2 | Soluble in both acids and strong bases |
| Fe2+ | Dirty white Fe(OH)2 | Insoluble in excess base | Turns dirty green in air as it oxidizes |
| Fe3+ | Reddish-brown gelatinous Fe(OH)3 | Insoluble in excess base | Gives blood-red color with NH4SCN |
Lesson 2: Qualitative Analysis of Basic Radicals (Cations) · 4 / 4
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