Organic compounds and their role in everyday life
Domain 6 - orgaanilised ühendid ja nende roll igapäevaelus - tests the hydrocarbons, alcohols, carboxylic acids and polymers you meet as fuels, solvents, food and plastics, and the formulas that distinguish them.
Hydrocarbons
- Carbon forms four bonds and can chain; alkanes CₙH₂ₙ₊₂ (methane CH₄, ethane C₂H₆, propane C₃H₈, butane C₄H₁₀) are saturated and burn cleanly with enough oxygen.
- Alkenes CₙH₂ₙ (ethene C₂H₄) contain a C=C double bond and decolourise bromine water - the standard test.
- Natural gas is mainly methane, LPG is propane/butane, petrol and diesel are alkane mixtures from oil.
Oxygen-containing compounds
- Alcohols contain –OH: methanol CH₃OH (toxic, causes blindness), ethanol C₂H₅OH (drinks, solvent, fuel), glycerol C₃H₅(OH)₃ (moisturisers).
- Ethanol is made by fermentation of glucose (C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂) with yeast, and industrially by hydration of ethene.
- Carboxylic acids contain –COOH: methanoic HCOOH (ant stings), ethanoic CH₃COOH (vinegar, about 5 %). They turn litmus red and react with carbonates, releasing CO₂.
- Fats and oils are esters of glycerol and fatty acids; carbohydrates include glucose, starch and cellulose; proteins are built from amino acids.
Polymers
- Addition polymers: ethene → polyethene, chloroethene → PVC, styrene → polystyrene. They are long, unreactive chains, slow to decompose, so sorting and recycling matter.
Worked example
How do you tell ethanol from ethanoic acid with two tests? Add universal indicator: ethanol is neutral (pH ≈ 7), ethanoic acid is acidic (pH ≈ 3). Add sodium carbonate: ethanoic acid fizzes (2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂), ethanol gives nothing. The carbonate test is decisive because it detects the –COOH group.
Traps that cost marks
- Swapping the alkane and alkene general formulas.
- Confusing methanol and ethanol - methanol is not drinkable.
- Describing vinegar as pure ethanoic acid, or as an alcohol.
- Saying ethanol burns without products: CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O.
- Thinking 'organic' means only from living organisms - urea and plastics are made industrially.