7. Organic chemistry (alkenes, combustion of alkenes) Flashcards
What is an alkene?
An unsaturated hydrocarbon with the general formula CnH2n
What do alkenes contain?
C = C (double bonded carbons)
What is the bromine test for alkenes?
- Add bromine water to an alkene
- If alkene is present there is a colour change from orange to colourless
Why are alkenes very reactive?
they are very unstable, due to the carbon-carbon double bonds, so the carbons will react with anything to go back to its stable form
Describe the combustion of alkenes?
alkenes burn with a smoky flame due to incomplete combustion
What are the 3 addition reactions for alkenes?
- Hydrogenation
- Hydration
- Halogenation
What is hydrogenation?
reacting an alkene with hydrogen gas to produce an alkane
What is the process of hydrogenation?
- React alkene with hydrogen
- With high temperatures (150 degrees Celsius) and a Nickel catalyst
What is hydration?
reacting an alkene with water to produce an alcohol
What is an alcohol?
An organic compound that contains an -OH functional group
What is the process of hydration?
- React an alkene with steam
- High temperatures, high pressure and acid catalyst (phosphoric acid)
What is halogenation?
reacting an alkene with a halogen to produce a haloalkane
What is the process of halogenation?
- An alkene is reacted with a halogen
- Reaction readily occurs at room temperature
State the characteristics of methanol, ethanol, propanol and butanol
- dissolve in water to form a neutral solution
- react with sodium to form hydrogen
- burn in oxygen
- react with carboxylic acids in presence of acid catalysts to form esters
What are 3 uses of alcohols?
- fuels
- as a solvent in industry
- drinks
What are the properties of alcohols?
- they can be oxidised to carboxylic acids
- they are flammable
- they are soluble
- they have a pH of 7
State the conditions required for the fermentation of glucose
- 30 degrees celsius
- aqueous solution of the glucose
- absence of air
- yeast added
State the chemical equation for a fermentation reaction?
C6H12O6 (glucose) → 2 C2H5OH (ethanol) + 2 CO2 (carbon dioxide)
What are carboxylic acids?
Organic compounds that contain a -COOH functional group
State the characteristics of carboxylic acids
- dissolve in water to form an acidic solution
- react with metal carbonates to form carbon dioxide
- react with alcohols with an acid catalyst to form esters
- react with metals to give off hydrogen gas
What type of acid is carboxylic acid?
a weak acid
Explain why carboxylic acids are weak acid?
- They are partially dissociated in water
- thus the pH of a carboxylic acid in solution is not as low as the pH of a solution of a strong acid of the same concentration
What is an ester?
An organic compound with a -COO- functional group
How is an ester formed?
from carboxylic acid and alcohol in the presence of a sulfuric acid catalyst
What kind of smell does an ester have?
a fruity or sweet smell
What is the test to distinguish between alkanes and alkenes?
bromine water test
What is the general formula for carboxylic acids?
CnH2n+1COOH
How can multiple alkenes form polymers when reacted together?
multiple alkenes can break the double bond when reacting and form new carbon-carbon bonds forming polymers
What is the general formula for alcohols?
CnH2n+1OH
Is ethene a renewable or non-renewable resource?
non-renewable as it is made from crude oil
Ethanoic acid + ethanol produces…?
ethyl ethanoate
What is a functional group?
that part of the compound that reacts
What are the first 4 members of the homologous series of alkenes?
- ethene
- propene
- butene
- pentene
Why are alkenes unsaturated?
alkenes have carbon-carbon double bonds (C=C) which means they have fewer hydrogens than their corresponding alkanes
