Chemistry III: Inorganic and Environmental Chemistry
❦
Periodic Trends and Groups
| Group or block | Key ideas |
|---|---|
| Group 1 | Reactivity increases down; flame colours (Li red, Na yellow, K lilac); Na⁺ and K⁺ are vital ions in the body (nerve impulses, fluid balance) |
| Group 2 | Mg²⁺ and Ca²⁺ in biology (chlorophyll, bones and teeth, muscle contraction); solubility trends |
| Group 13 | Aluminium: amphoteric oxide; uses |
| Group 14 | Carbon allotropes; silicon; tin and lead (lead is a toxic metal) |
| Group 15 | Nitrogen and phosphorus: ammonia, nitrates, phosphates, fertilizers; ATP and DNA contain phosphate |
| Group 16 | Oxygen, ozone, sulfur; sulfuric acid; hydrogen peroxide (an antiseptic) |
| Group 17 | Halogens; oxidizing power decreases down; fluoride in dental health; iodine in thyroid hormones; chlorine in water treatment |
| Group 18 | Noble gases; helium and xenon have medical uses |
| d-block | Variable oxidation states; coloured ions; catalysts; complex ions. Iron in haemoglobin, zinc in enzymes, copper and cobalt (vitamin B₁₂) |
Complex Ions and Biology
Haemoglobin contains iron(II) in a porphyrin complex; carbon monoxide binds more strongly than oxygen, causing poisoning. Chelation therapy removes toxic metals; the anticancer drug cisplatin is a platinum complex.
Qualitative Analysis (Summary)
| Ion | NaOH (a few drops) | Excess NaOH |
|---|---|---|
| Al³⁺ | White precipitate | Dissolves |
| Zn²⁺ | White precipitate | Dissolves |
| Pb²⁺ | White precipitate | Dissolves |
| Fe²⁺ | Green precipitate, darkening in air | Insoluble |
| Fe³⁺ | Red-brown precipitate | Insoluble |
| Cu²⁺ | Pale blue precipitate | Insoluble |
Anion tests: carbonate (effervescence with acid); sulfate (white precipitate with acidified BaCl₂); chloride (white precipitate with AgNO₃, dissolving in dilute ammonia); nitrate (brown ring test). Record observations separately from inferences.
Industrial Chemistry
The Haber process (iron catalyst; about 400 to 450 °C; about 200 atm) makes ammonia for fertilizer. The Contact process (V₂O₅; about 450 °C) makes sulfuric acid. The Ostwald process makes nitric acid. Chlor-alkali electrolysis gives chlorine and sodium hydroxide. Pharmaceutical manufacture, water treatment, and soap production are applications of chemistry in health.
Environmental Chemistry
Ozone depletion by chlorofluorocarbons, the greenhouse effect, acid rain, photochemical smog; water quality (dissolved oxygen, BOD, COD), eutrophication; heavy metals and pesticides in the food chain; waste management. Green chemistry (Anastas & Warner, 1998) seeks to prevent waste and to use safer chemicals. Link these topics with Chapter 13.
Laboratory Safety
Know hazard symbols, wear eye protection, handle acids and bases with care, and dispose of waste correctly.
Common Mistakes
- Memorizing reactions without understanding trends.
- Confusing observations with conclusions.
- Forgetting catalysts and conditions in industrial processes.
CHAPTER 18