1 / 16

Unit 2 The World of Carbon

Unit 2 The World of Carbon. Fuels. -substances which burn releasing energy. Petrol – from fractional distillation of crude oil and reforming of naphtha fraction. Reforming produces - branched chain alkanes, - cycloalkanes

della
Download Presentation

Unit 2 The World of Carbon

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Unit 2 The World of Carbon

  2. Fuels -substances which burn releasing energy. Petrol – from fractional distillation of crude oil and reforming of naphtha fraction. Reforming produces - branched chain alkanes, - cycloalkanes - aromatic compounds. - decreases ‘knocking’ from auto-ignition. Lead compounds improve combustion but no longer used. Winter petrol blends have more volatile hydrocarbons than summer blends.

  3. Alternative fuels Ethanol - from fermentation of sugar cane; renewable. Methanol - from synthesis gas (from steam reforming of CH4) Advantages: virtually complete combustion; no aromatic carcinogens; cheaper than petrol; less explosive than petrol Disadvantages: absorbs water making in corrosive to engine; toxic; increases greenhouse gases unless CH4 from biogas Methane- renewable if formed by anaerobic fermentation of organic waste e.g. manure; main constituent of biogas. Hydrogen – can be produced by electrolysis of water using solar energy; clean burning, only produces water; difficult to store and distribute.

  4. Hydrocarbons Compounds of hydrogen and carbon only Homologous series: families of compounds which • share general formula • have similar chemical properties (react the same) • show regular changes in physical properties with increasing size (by CH2 each time)

  5. Hydrocarbons Alkanes • CnH2n+2 • single C-C bonds, saturated • slow, substitution reactions Cycloalkanes • CnH2n • single C-C bonds, saturated cyclic compounds • slow, substitution reactions Alkenes • CnH2n • at least 1 double C=C bond, unsaturated • fast, addition reactions

  6. Hydrocarbons Alkynes • CnH2n-2 • at least 1 triple C=C bonds, unsaturated • fast, addition reactions Naming hydrocarbons Name indicates • number of carbon atoms in molecule: meth-1, eth-2, prop-3, but-4, pent-5, hex-6, hept-7, oct-8 (monkeys eat peanut butter penguins hate hairy oranges) • family e.g. -ane, -ene, -yne

  7. Naming hydrocarbons Choose longest carbon chain, be sure to include functional group e.g. double bond Number carbons, if any branches are present keep numbers as low as possible (this might mean going from right to left!) e.g. Branches name indicates number of carbons -CH3, methyl; -C2H5, ethyl; -C3H7, propyl etc Isomers – same molecular formula, different structures (moving double bond produces isomer)

  8. Addition reactions Alkenes addition of • a halogen (1) • hydrogen (2) • a hydrogen halide (3) • water (4)

  9. Addition reactions Alkynes • two-stage process: • alkyne→ alkene→ alkane • possibility of isomers being produced. • compared to an alkene, complete addition to an alkyne will require twice the quantity of • halogen (1) • hydrogen (2) • hydrogen halide (3)

  10. Aromatic compounds • Benzene • very important feedstock • ‘mother’ of all aromatics • C6H6 • does not decolourise bromine rapidly, hence saturated • each carbon forms only 3 bonds, leaving a ‘spare’ electron • the ‘spare’ electrons can move (delocalised) around the ring

  11. Aromatic compounds • basically benzene with at least 1 hydrogen substituted with • another atom/group of atoms • phenyl group, -C6H5 benzene ring minus 1 hydrogen • used in manufacture of, e.g., plastics (including Bakelite), • explosives, drugs, dyes

  12. Alcohols (Alkanols) • contain the hydroxyl functional group, -OH • names end in –ol e.g. methanol CH3OH; ethanol C2H5OH • need to specify carbon with –OH from propanol onwards • when naming, longest carbon chain must include –OH • e.g. • primary alcohols (with exception of methanol) have 1 C • attached to –COH, secondary alcohols have 2C, tertiary have • 3C attached to -COH

  13. Reactions of alcohols • made by catalytic hydration of alkenes or reduction of ketones • and aldehydes • dehydrated, using aluminium oxide as a catalyst, to alkenes • undergo combustion producing carbon dioxide and water • primary and secondary alcohols undergo partial oxidation • with mild oxidising agents: • - acidified potassium dichromate (H+/Cr2O72-, orange to green) • - acidified potassium permanganate (H+/MnO4-, purple to colourless) • - hot copper (II) oxide (black to red)

  14. Partial oxidation of alcohols • primary alcohols partially oxidised to alkanals (aldehydes) which • can be partially oxidised further to alkanoic acids • secondary alcohols partially oxidised to alkanones (ketones), • these cannot be further partially oxidised • tertiary alcohols do no undergo partial oxidation

  15. Alkanals (aldehydes) and alkanones (ketones) • made by partial oxidation of primary and secondary alkanols • (alcohols) (see previous slide) • can be reduced to the alcohol from which they were made • aldehydes can be further partially oxidised to alkanoic acids • contain the carbonyl group, C=O • carbonyl group polar as O greater electronegativity than C • when naming, carbon chain must include carbonyl group • number carbons from end closest to carbonyl group e.g.

  16. Experimentally distinguishing aldehydes from ketones • ketones are resistant to partial oxidation, because the carbonyl • group is flanked by two C atoms • alkanals (aldehydes) can be partially oxidised to the • corresponding alkanoic acid

More Related