Organic chemistry Flashcards
What are the two ways cracking can be done
-Passing alkane vapour over a catalyst
-Mixing alkane vapour with steam
Before heating to a very high temperature
Where would cracking place in industry?
Cracking unit in fractional distillation column
How would cracking happen in a lab
Porcelain chips would act as catalyst. Vapour would be passed over hot powdered aluminium oxide catalyst
Long chain molecules split apart on surface of specks of catalyst
How can you crack carbons with vapour?
Mix with steam, and heat to high temp
How can product gas prove it has alkenes in it?
Bubble through bromine water because alkenes more reactive than alkanes and so they react with bromine water turning this liquid from orange to colourless.
What is an alkene
A hydrocarbon with a double c=c bond (covalent)
What is the formula for alkenes
CnH2n
Why do alkenes not have methane as part of their series
Because methane is one carbon and alkenes have to have a double bond so need more than one carbon
Why are alkene molecules unsaturated
Because they contain fewer hydrogen atoms than the alkane with the same number of carbon atoms
Name the first 4 alkenes
Ethene
Propene
Butene
Pentene
Explain but-1-ene
Means the double bond is in the first c-c bond of the butene molecule
How are alkenes more reactive than alkanes?
The c=c bond can open make a single bond allowing 2 carbon atoms to bond with other atoms
Which hydrocarbon fractions are in the greatest demand?
Fractions containing smaller hydrocarbons- used for fuels. Global demand for small hydrocarbons high and excess of large. Solution is cracking.
Larger carbons for Road surfacing e.g. Bitumen
How do most alkenes react
Via addition reactions.
C=c bond will open up and leave a single bond and a new atom to each carbon
What 4 reactions do alkenes undergo?
Hydrogen
Oxygen
Halogens
Water (steam)
Explain alkene reaction with hydrogen
Saturated alkANE made.
Reaction called hydrogenation and occurs at 150°c with nickel catalyst
Explain alkene reaction with oxygen
Combustion reactions.
Don’t generally combust alkenes however because:
Burn with smokey flame due to incomplete combustion
Useful as starting materials for making polymers, alcohols, medicines
Explain alkene reaction with halogens
Addition reaction.
Hydrogen atoms added across c=c bond to make any c-c bond (saturated)
Explain alkene reaction with water (steam) and explain what conditions are required
Addition reaction
OH, H added across c=c bond: hydration reaction.
High temps, high pressure and concentrated phosphoric catalyst needed.
What is the alcohol functional group and how does the unit differ
- OH-
- ch2h-
What are the 4 reaction with alcohols
Water
Oxygen
Oxygen
Sodium metal
Explain reaction of alcohol with water
Alcohols posses covalent bonds that do not break easily, so dont react with water other than dissolve in it. Eg ethanol in vodka
Explain reaction of alcohol with oxygen (combustion)
Alcohols are flammable and burn in air why often used as fuels. Eg spirit burners. Burn cleanly and not smelly.
Produce co2 and h20
Explain reaction of alcohol with oxygen (mild oxidation)
A mild oxidising agent will gently add oxygen or remove hydrogen from a mol without breaking it apart.
Oxidising agents: O2 in air, microbes.
Produce CARBOXYLIC ACID
What is the most common example of alcohol with oxygen?
Wine containing ethanol oxidised in air to make vinegar (ethanol acid)
Explain the reaction of sodium metal with alcohol
Produce a hydrogen gas and basic solution.
Give 2 other uses of alcohols
Good solvents-n used to dissolve perfume molecules and medicines that are not soluble in water.
Aq solutions of ethanol are produced when sugar solutions are fermented using yeast- FERMENTATION.
Yeast
Sugar———> ethanol + co2
Conditions: yeast, no oxygen, room temp
What is crude oil
A finite resource
Mixture of large compounds (hydrocarbons)
How many bonds does an alkane have
1
What is an homologous series?
A group of compounds that react in similar ways
How do alkanes differ from one and other
CnH2n+n
What are the first 4 alkanes
Methane
Ethane
Propane
Butane
What is the smallest and biggest hydrocarbon
Methane and bitumen residue
Describe the process of fractional distillation
1.Crude oil is heated and most evaporated to vapour
2.Gases enter fractioning column and liquid drains off
There’s a temp gradient in the column- hot at bottom cooler as you go up
3. Longer HCs condense back into liquid and drain out of column near bottom because higher boiling point
4. Shorter HCs condense and drain out much later on at top of column because lower boiling point.
What is the final result of fractional distillation
Crude oil mixture separated into different fractions. Each fraction contains a mixture of HCs- similar number of carbon atoms and similar boiling points
What is fractional distillation?
HCs separated into fractions each containing molecules with similar number of carbon atoms.
These fractions can be processed to produce fuels and feedstock for chemical, industry eg. Make medicines or plastics.
What do the properties of hydrocarbons depend on
Their size
What factors influences how hydrocarbons are used as fuels?
Boiling point
Flammability
Viscosity
Describe boiling point
Larger molecule higher
Because greater intermolecular forces require more heat/ energy to gain enough speed or energy to leave the surface of the liquid and become a gas
Describe flammability
Smaller mol burn easier- used for fuels- weaker
Larger mol tend not to burn
Describe viscosity
Larger mol more tangled posses greater intermolecular forces less able to move past each other
Like spaghetti
What happens in the combustion of hydrocarbons
H oxidised to form H2O
C oxidised to form CO2
Energy given out in form of heat and light
Hydrogen+oxygen—> H2O+CO2
What is cracking
Thermal decomposition (large alkanes heated to vapour and broken up)
What is made in cracking
Mixture of alkenes and alkanes
What is the functional group of carboxylic acids
COOH
What do carboxylic acids react with
Water
Carbonates
Alcohols
How does a carb acid react with water
They dissolve easily in water
The partially ionic OH bond will partially react with water by partially dissociating to form carboxylate ion (COO)
Describe the dissociation process
Called IONISATION
results in production of H+ ions making solution acidic
As dissociation only partial only some H+ ions are made at one time and acid solution is weak- weak acids
Describe reaction of carb acid with carbonate
Form salt co2 and water
Describe carb acid with alcohols
Can be reacted together if small amount of concentrated sulfuric acid present to act as catalyst
Mol of water is removed from carb acid and alcohol and remaining fragments combine together
Conc of sulfuric acid able to catalyse reaction because it absorbs the water strongly encouraging reaction to proceed
ESTER IS MADE -COO
