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Identify hydrocarbons and alkene test results

Organic chemistry • Carbon compounds as fuels

Key concepts

What you'll likely be quizzed about

  • Hydrocarbons contain only carbon and hydrogen.
  • They include alkanes and alkenes, defined by carbon-carbon bonding.
  • Alkanes have single bonds, while alkenes possess at least one double bond, affecting their chemical behavior.

Flashcards

Test your knowledge with interactive flashcards

What is the classification of C2H4?

Click to reveal answer

C2H4 is an alkene (ethene) fitting CnH2n.

Key notes

Important points to keep in mind

Alkanes follow CnH2n+2 for straight-chain, non-cyclic molecules.

Alkenes follow CnH2n for one double bond in straight-chain molecules.

Convert condensed or displayed formulas to atom counts to compare with general formulas.

Bromine water decolorises (orange → colourless) in the presence of carbon–carbon double bonds.

Bromine water remains orange with alkanes under normal laboratory conditions.

Consider rings and heteroatoms before classifying by simple formulas.

False positives can occur; corroborate the bromine test with structural or spectroscopic evidence.

Count carbons (n) first, then calculate expected hydrogens using the general formula.

Displayed formulas show bonds and help confirm single vs double bonds.

Empirical formulas give ratios, not necessarily exact molecular composition.

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