Organic Chemistry

covers the production and uses of hydrocarbons - including alkanes, alkenes, carboxylic acids and esters

source of hydrocarbons

source of hydrocarbons

crude oil

hydrocarbons

molecules made up of only hydrogen and carbon atoms

uses of crude oil

fuel (from the hyrdocarbons) and tarmac (from the tar)

long chain hydrocarbons properties

higher viscosity

less flammable

higher boiling points (low volatility)

short chain hydrocarbons properties

lower viscosity

more flammable

lower boiling points (high volatility)

Explain the steps involved in the fractional distillation of crude oil.

1. Crude oil is heated and vaporised. The vapour enters a fractionating column at the bottom.

2. The vapour rises up the column, decreasing in temperature as it rises.

3. The gases condense as they reach their boiling points, so different fractions collect as liquids on different levels.

4. Fractions leave the fractionating column as liquids.

complete combustion equation

hydrocarbon + oxygen → carbon dioxide + water

incomplete combustion equation

hydrocarbon + oxygen → carbon monoxide + water (+soot)

cracking

the process of decomposing long-chain hydrocarbon molecules into shorter chain hydrocarbons.

why do we crack hydrocarbons?

Short chain hydrocarbons are most useful, so are in higher global demand.

general equation for hydrocarbon cracking

large chain alkane — (500°C and catalyst of steam) → smaller chain alkane(s) + alkene(s)

general formula of alkenes

C_nH_2n

general formula of alkanes

C_nH_2n+2

first 4 prefixes of hydrocarbons

meth-

eth-

prop-

but-

homologous series

a ‘family’ of hydrocarbons which share the same general formula and similar chemical properties

are alkenes saturated and why?

Unsaturated because they contain a double carbon bond

what is the shortest alkene?

ethene

functional group of alkenes

C=C

addition reaction

when a double bond opens up allowing new atoms to bond

alkenes and halogens

React together to form a compound

A colour change takes place

Used as a test to distinguish between alkanes and alkenes

alkenes and hydrogen reaction

React together to form an alkane

Uses nickel as a catalyst

alkenes and water reaction

React together to form an alcohol

Uses phosphoric acid as a catalyst

combustion of alkenes

Incomplete combustion

Produces carbon monoxide + carbon + water

Burn with smoky flames

functional group of alcohols

OH

general formula of alcohols

C_nH2_n+1OH

uses of alcohols

alcoholic drinks

as solvents - perfumes, steriliser etc - many chemicals that are insoluble in water are soluble in alcohol

fuels - spirit burners, biofuels

alcohols and water reaction

mix easily to form neutral solutions

alcohols with smaller molecules mix better

combustion of alcohols

complete combustion - burn easily

produce carbon dioxide and water

alcohols with bigger molecules burn less cleanly, with a yellow flame

alcohols and sodium reaction

reacts to give sodium alkoxide and hydrogen

gentle fizzing and sodium slowly dissolves

oxidisation of alcohol

forms a carboxylic acid and water

colour change from orange to green

fermentation

common method for producing ethanol

fermentation equation

sugar solution + yeast → ethanol + carbon dioxide

conditions for fermentation

temperature of 37°C

slightly acidic solution

no oxygen (anaerobic reaction)

general formula of carboxylic acids

C_nH_2n+1COOH

functional group of carboxylic acids

COOH

are carboxylic acids weak or strong?

weak acids, because they only partially ionise in water

carboxylic acids and water reaction

form an acidic solution

carboxylic acids and alcohols reaction

react to form an ester and water

uses an acid catalyst

carboxylic acids and carbonates reaction

react to give a salt, carbon dioxide, and water

functional group of esters

COO

production of esters

made when carboxylic acids react with alcohols

condensation reaction - water is the other product

properties of esters

volatile (evaporate easily)

many have pleasant smells - used to produce perfumes