Organics Flashcards
Crude oil
A mixture of unrefined hydrocarbons
How is crude oil formed?
- Millions of years ago, huge numbers of plankton died and fell to the bottom of the sea. Their remains were covered by mud
- As the mud was buried further, and the temperature and pressure increased, it started to change into rock. The dead plankton were slowly cooked, changing gradually into oil
- The oil rose due to pressure from below, getting trapped under impermeable rocks, such as those in the sedimentary layer of the Earth’s crust
Hydrocarbon
A compound made up of carbon and hydrogen atoms only
How are the following properties affected as the number of carbon atoms in a hydrocarbon increases:
- Boiling point
- Darkness of hydrocarbon
- Viscosity
- Flammability
- Smokiness of flame
Boiling point: increases Darkness: increases Viscosity: increases Flammability: decreases Smokiness: increases
Fractional distillation
Used to separate hydrocarbons of different sizes into fractions
How does fractional distillation work? (4 points)
- All of the crude oil is heated and vaporised
- It is then fed into a fractionating tower
- This is hot at the bottom and cold at the top
- The hydrocarbons rise up the tower and condense at different points due to their differing boiling points
- As each fraction contains a mixture of hydrocarbons, the boiling point of each fraction is a range
Why is the boiling point of each fraction a range?
Each fraction contains a mixture of different hydrocarbons
Order the following six in order of increasing boiling point and give a use for each: Bitumen Gasoline Refinery gases Diesel oil Kerosene Fuel oil
- Refinery gases: everyday cooking
- Gasoline: petrol
- Kerosene: jet fuel
- Diesel oil: diesel fuel
- Fuel oil: ship fuel
- Bitumen: road tar
Combustion reaction
A chemical reaction where a compound and an oxidant react to produce heat and a new product
Fuel
A substance that reacts with oxygen to release useful energy, mostly as heat energy
What are the two kinds of combustion?
- Incomplete
2. Complete
Complete combustion:
- When does it occur?
- General word equation
- When there is a steady supply of oxygen
2. Hydrocarbon + oxygen → carbon dioxide + water
Incomplete combustion:
- When does it occur?
- General word equation
- When the supply of oxygen is poor
2. Hydrocarbon + oxygen → carbon monoxide + carbon + water
How can the occurrence of incomplete combustion lead to death?
Carbon monoxide is poisonous. It can be fatal if inhaled, as it cuts off oxygen supply by binding irreversibly to the haemoglobin in red blood cells
Three common air pollutants and how they are formed
- Carbon monoxide: incomplete combustion of the fuel in car engines
- Nitrogen oxides: formed from the heat and pressure found in a car engine
- Sulphur dioxide: sulphur impurities in fuels burn
How are nitrogen oxides formed?
The energy from the spark plug in a car is sufficient for the usually unreactive nitrogen gas in air to react with oxygen
What hazards does the emission of nitrogen oxides lead to?
- They react with other pollutants in sunlight to form a photochemical smog, causing breathing difficulties
- Acid rain
What hazard does the emission of sulphur dioxide lead to?
Acid rain
What effects does acid rain have on the environment?
- Kills plants
- Poisons aquatic life
- Erodes stonework e.g. limestone
- Corrodes metals
Steps for experiment to separate crude oil into fractions
- Pour crude oil into a boiling tube
- Fit a thermometer into the boiling tube
- Connect a delivery tube to the boiling tube
- Heat the crude oil gently at first, then more strongly
- Collect each fraction in a different test tube
Which two methods can you use to confirm that water is formed during complete combustion?
- Cobalt chloride paper should turn pink
2. Anhydrous copper sulphate should turn blue
How can you confirm that carbon dioxide is formed during complete combustion?
Limewater should turn cloudy
Why are shorter hydrocarbons more useful?
- More flammable
- Burn for longer
- Less smoky i.e. cleaner
Catalytic cracking
The process by which longer chain alkanes are broken down into more useful products
What is catalytic cracking an example of?
Thermal decomposition
What two conditions are needed for catalytic cracking?
- Silicon dioxide OR aluminium oxide catalyst
2. High temperature (600–700˚C)
Two types of hydrocarbon compounds
- Alkanes
2. Alkenes
What is the general formula for:
- Alkanes?
- Alkenes?
- CnH2n+2
2. CnH2n
What are the two general product outputs of cracking a hydrocarbon?
- All alkenes + hydrogen
2. Alkenes + an alkane (no hydrogen)
What are the three different kinds of formulae?
- Molecular: shows how many atoms there are of each element in the compound
- Structural: a written formula showing how the atoms are bonded together
- Displayed: a diagram showing all the bonds within the molecule
What is the molecular formula for butane?
C₄H₁₀
What is the structural formula for butane?
CH₃CH₂CH₂CH₃
What is the displayed formula for butane?
H H H H
| | | |
H–C–C–C–C–H
| | | |
H H H HDraw the displayed formula for CH₃CH₂CH₂OH
H H H
| | |
H–C–C–C–O–H
| | |
H H HSteps to name a molecule
- Figure out the stem name
- Alkane or alkene?
- Position of the double bond (in an alkene)
- Any branches
What is the stem name based on?
The longest number of carbon atoms in a chain
List the first five stem names for hydrocarbons
- Meth–
- Eth–
- Prop–
- But–
- Pent–
What is the saturation of:
- Alkanes?
- Alkenes?
- Fully saturated - all single bonds
2. Unsaturated - has a double bond
What is the suffix for:
- Alkanes?
- Alkenes?
- –ane
2. –ene
How do you find the position of the double bond in an alkene?
- Number the carbon atoms 1 to n in series
- Number them in the direction that produces the smallest numbers in the molecule name
- This number goes between the stem name and the –ene e.g. but-2-ene
Give the molecule name for the following: H H H H | | | | C=C–C–C–H | | | H H H
But-1-ene
Give the names for the following branch side chains:
- –CH₃
- –CH₂CH₃
- Methyl–
2. Ethyl–
What is the following molecule called?
H
|
H–C–H
H | H H H
| | | | |
H–C–C–C–C–C–H
| | | | |
H H H H H2-methyl pentane
What is the following molecule called?
H
|
H–C–H
H H | H
| | | |
C=C–C–C–H
| | |
H H H3-methyl but-1-ene
What does the suffix –ol denote?
Alcohol - ends in OH
How many bonds do the following atoms have:
- Carbon
- Hydrogen
Carbon: 4
Hydrogen: 1
Structural isomers
Molecules with the same molecular formulae, but different structural formulae
What are different isomers the result of?
Differences in branching
Give the names and displayed formulae for the two isomers of butane (C₄H₁₀)
H
|
H–C–H
H H H H H | H
| | | | | | |
H–C–C–C–C–H H–C–C–C–H
| | | | | | |
H H H H H H H
Butane 2-methyl propane
Why do more carbon atoms in a chain lead to a higher boiling point?
The intermolecular forces are stronger
Homologous series
A series of compounds that have similar properties and the same general formula
What characteristics do homologous series have?
- Same functional group
- Differ by CH₂
- Same general formula
- Trend in physical properties
- Similar chemical properties
What is the trend in physical properties for straight chain alkanes?
1–4 are gases, 5+ liquids
Reactions of alkanes
- Combustion (complete and incomplete)
2. Substitution reaction with bromine (requires UV light)
Reactions of alkenes
- Combustion (complete and incomplete)
2. Addition reaction with bromine (no UV light needed)
Why don’t people use alkenes in combustion reactions?
The presence of a double bond makes them more useful for other things
Substitution reaction of methane with bromine
Methane + bromine → bromomethane + hydrogen bromide
CH₄ + Br₂ → CH₃Br + HBr
*UV light needed
Addition reaction of ethene with bromine
Ethene + bromine → dibromoethane
C₂H₄ + Br₂ → C₂H₄Br₂
*no UV light needed
How would you test for an unsaturated hydrocarbon?
The reaction with bromine: alkenes turn the solution colourless quickly
What colour is:
- Bromine water?
- The products of the reactions of bromine with both alkanes and alkenes?
- Orange-brown
2. Colourless
