AS - Unit 2 - Basic concepts and hydrocarbons Flashcards
What is a hydrocarbon?
An organic compound that contains carbon and hydrogen only
What is a saturated hydrocarbon?
A hydrocarbon with single bonds only
What is an unsaturated hydrocarbon?
A hydrocarbon containing carbon-to-carbon multiplde bonds
What is an aliphatic hydrocarbon?
A hydrocarbon with carbon atoms joined together in straight or branched chains
What is an alicyclic hydrocarbon?
A hydrocarbon with carbon atoms joined together in a ring structure
What is a functional group?
The part of the organic molecule responsible for its chemical reactions
What is a homologous series?
A series of organic compounds with the same functional group but with each successive member differing by CH2
What is an alkane?
A homologous series with the general formula CnH2n+2
What is the shape and angle of carbon atoms in an alkane?
A tetrahedral shape with a bond angle of 109.5
What is nomenclature?
The system of naming compounds
What is an alkyl group?
A alkane with a hydrogen atom removed e.g. CH3, C2H5. Any alkyl group is often shown as R
What is empirical formula?
The simplest whole-number ratio of atoms of each element present in a compound
What is molecular formula?
The actual number of each element in a molecule
How do you calculate empirical formula?
Divide the percentages by their elements relative formula mass
then multiply the answers by the smallest answer there
you should get a simple ratio
that is the empirical formula
How do you calculate molecular formula?
Find the relative empirical mass of the empirical formula
then divide the relative molecular mass by the relative molecular mass by the relative empirical mass
The number you are left with is how many times larger the formula is than the empirical formula
What is general formula?
The simplest algebraic formula for a member of a homolgous series
What is a displayed formula?
The relative positioning of all the atoms in a molecule and the bonds between them
How is structural formula useful in chemistry?
It shows the minimal detail for the arrangement of atoms in a molecule
Explain skeletal formula
It is a simplified organic formula, the hydrogen atoms are removed from alkyl chains, leaving just a carbon skeleton and associated functional groups
What are structural isomers?
Molecules with the same molecular formula but with different structural arrangements of atoms
What are stereoisomers?
Compounds with the same structural formula, but with different arrangement of the atoms in space
What is E/Z isomerism?
A type of stereoisomerism in which different groups attached to each carbon of a C=C double bond may be arranged differently in space because of the restricted rotation of the C=C bond
What is cis-trans isomerism?
A special type of E/Z isomerism in which there is a non-hydrogen group and hydrogen on each C of a C=C double bond.
How is a cis isomer (Z isomer) displayed?
(Z isomer) has the H atoms on each carbon on the same side
How is a trans isomer (E isomer) displayed?
(E isomer) had the H atoms on each carbon on different sides
When naming E/Z isomers, in which order are the groups attached to the double bond named?
Based on their atomic number.
Group with the highest atomic number is given highest priority
What is homolytic fission?
The breaking of a covalent bond, with one of the bonded electrons going to each atom, forming two radicals
What is a radical?
A species with an unpaired electron
What is heterolytic fission?
the breaking of a covalent bond with both of the bonded electrons going to one of the atoms, forming a cation and an anion.
What is a nucleophile?
an atom that is attracted to an electron-deficient centre or atom, where it donates a pair of electrons to form a new covalent bond
What is an electrophile?
A atom that is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond
What is an addition reaction?
A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule
What is a substitution reaction?
A reaction in which an atom or group of atoms is replaced with a different atom or group of atoms
What is an elimination reaction?
The removal of a molecule from a saturated molecule to make an unsaturated molecule
What does percentage yield measure?
The proportion of products formed in a reaction
What does atom economy measure?
The proportion of products that are used
What is fractional distillation?
The separation of the components in a liquid mixture into fractions which differ in boiling point and by means of distillation, typically using a fractionating column
How does chain length affect the boiling point of crude oil?
The shorter the chain the less points of contact there are between the molecules meaning there are less van der Waalsā forces holding it to other molecules, meaning less energy needed to break the bonds and thus a lower boiling point
How does branching of alkanes affect the boiling point of crude oil?
With a branched molecule there are less points of contact between molecules leading to fewer van der Waalsā forces between molecules.
Also branched molecules cant get as close to each other as unbranched molecules and therefore decreasing the intermolecular forces between the molecules and therefore lowering the boiling point
Give a reason for longer alkane chains being dangerous to use in cars
the longer chains donāt combust as easily and often undergo incomplete combustion, leaving carbon monoxide behind
Give two uses for short chained alkanes and alkenes
Alkane - Fuels
Alkene - Polymer production
What is cracking?
The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes
What is a catalyst?
A substance that increases the rate of a chemical reaction without being used up in the process
What different things are created by cracking?
Straight chain molecules into branches molecules
Straight chain molecules into cyclic molecules
Which kind of alkanes are most efficient in petrols?
Cyclic and branches molecules as they promote more efficient combustion than straight-chain alkanes
What is the H+ product of branching alkanes used for?
making margarine
ammonia production
What negative effects does burning hydrocarbons have on the environment?
Carbon monoxide - formed by incomplete combustion
Carbon dioxide - greenhouse effect
Nitrogen oxides - acid rain and destruction of forests
Sulphur dioxide - acid rain
Explain how biofuels can help the environment
Ethanol can be used by fermenting sugar and other carbohydrates
it burns efficiently in a plentiful supply of oxygen to produce carbon dioxide and water
ethanol can be blended with petroleum causing the fuel to burn more efficiently.
Significantly reduced harmful exhaust emissions
Which plant can be used to create biodiesel?
Rapeseed
can be used in compatible engines 100% pure but it is usually blended with normal diesel
What is radical substitution?
A type of substitution reaction in which a radical replaces a different atom or group of atoms
What is a mechanism?
A sequence of steps showing the path taken by electrons in a reaction
What are the three steps of radical substitution?
Initiation
Propagation
Termination
Explain the initiation stage of radical substitution
The bond in a chlorine molecule is broken by homolytic fission forming two chlorine radicals.
UV radiation provides the energy for this bond fission
Explain the propagation stage of radical substitution with reference to chlorination
Methane reacts with the Cl radical, a methyl radical is produced and HCl is also produced
Then the methyl radical reacts with a chlorine molecule forming chloromethane and a Cl radical again
Explain the termination stage of radical substitution with reference to chlorination
Cl + Cl = Cl2 (two radicals)
CH3 + CH3 = C2H6 (two radicals)
CH3 + Cl = CH3Cl (two radicals)
What is initiation?
The first step in a radical substitution in which the free radicals are generated by ultraviolet raditation
What is propagation?
The two repeated steps in radical substitution that build up the products in a chain reaction
What is termination?
The step at the end of a radical substitution when two radicals combine to form a molecules
What is a pi-bond?
The reactive part of a double bond formed above and below the plane of the bonded atoms by sideways overlap of p-orbitals
What is a sigma bond?
The electrons directly bonding the atoms together, showing the overlap of orbitals, each carbon atom in a C=C bond contributes one electron to the electron pair in the sigma bond
Why is there no free rotation in a double bond?
The pi bond fixes the carbon atoms in place at either end of the double bond, preventing any free rotation
What is the general shape of an alkene molecule?
Trigonal planar, with an angle of 120 degrees, there are three areas of electron pair repulsion
What is the average bond enthalpy of a C-C single bond?
+347
What is the average bond enthalpy of a C=C double bond?
+612
Why are alkenes more reactive than alkanes?
Because of the double bond
What do bond enthalpies tell you?
The general strength of a bond
What happens to the pi and sigma bonds when an alkene reacts?
The pi bond breaks and the sigma bond remains intact
What are the reagents and conditions when hydrogenating an alkene?
H2, Nickel catalyst and 150 degrees C
What is halogenation?
When you add an X2 (halogen molecule) to an alkene to form a di-substituted halogenalkane
What happens when you add bromine to an alkene?
The bromine will go from orange to colourless due to the double bond breaking and the bromine now being included in the alkene to form a halogenoalkane
How do you create ethanol from ethene?
Add H2O in the form of steam and an acid catalyst
What is Markovnikovās rule?
In a HX addition reaction the hydrogen of the HX becomes bounded to the carbon atom that has the greatest number of hydrogen atoms
What is electrophilic addition?
A type of addition reaction in which an electrophile is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond
`What is a carbocation?
A organic ion in which a carbon atom has a positive charge
What is a curly arrow?
A symbol used in reaction mechanisms to show the movement of an electron pair in the breaking or formation of a covalent bond
How do you add HBr onto an alkene?
HBr is polar, Br is more negative than H which causes a polar bond
Electron pain in the Pi bond is attracted to the polar H+ atom, breaking the double bond
New bond forms between one of the carbon atoms and the H atom
HBr bond breaks, electron pair going to the Bromine
Br- is formed and so is a carbocation on the alkene/alkane now
Carbocation is unstable and quickly forms a bond with the Br- ion to form an organic product
How do you add Br2 to an alkene?
As the bromine approaches the pi bond, the electrons in the pi bond repel the electrons in the Br2 bond, making the Br2 slightly polar
pi bond in alkene attracted to Br+ in the Br2 which causes the double bond to break
new bond formed between one of the carbon atoms and the bromine atom
The Br-Br bond breaks by heterolytic fission leaving a Br- ion to form with the carbocation left on the organic molecule
What is used to hydrogenate and alkene?
H2
Ni catalyst
150 degrees C
How do you make an alcohol from and alkene?
Steam
H3PO4 catalyst
High temp
High pressure
What is a polymer?
A long molecular chain built up from monomer units
What is a monomer?
A small molecules that combines with many other monomers to form a polymer
What is addition polymerisation?
The process in which unsaturated alkene molecules (monomers) add on to a growing polymer chain one at a time, to form a very long saturated molecular chain (the addition polymer)
What is an addition polymer?
A very long molecular chain, formed by repeated addition reaction of many unsaturated alkene molecules
Which process makes poly(phenylethene), poly(styrene) and branched poly(ethene)?
Radical polymerisation
When was the first margarine invented?
1909
When was poly(styrene) first created?
1930
When was PVC first created?
1938
What is repeat unit?
A specific arrangement of atoms that occurs in the structure over and over again.
Repeat units are given in brackets outside of which is the symbol ānā
What is biodegradable material?
A material that is broken down naturally in the environment by living organisms
Give some uses for polystyrene
foam packaging
model-making in the food retail trade
Give some uses for poly(propene)
Food packaging
dishwasher safe containers
fibre in carpets
synthetic ropes
Give some uses for polythene
Grocery bags
Shampoo bottles
Toys
What two stages are involved in recycling?
Sorting
Reclamation
How are plastics sorted to be recycled?
Scanning techniques to separate PET from HDPE
When PET bottles are recycled what are they made into?
Carpets
clothing
new bottles
When HDPE plastic is recycled what is it made into?
Re-used to make hard plastic materials such as boxes, water butts and bins
When LDPE plastic is recycles what is it made into?
Plastic refuse sacks
Some polymers are used as fuels, explain how this is possible
Burning under controlled conditions, produces heat energy can be harnessed to make electricity
What are biodegradable plastic bags made out of?
Starch, maize, cellulose, lactic acid
Give some positives of biodegradable plastics
Break down as a result of bacterial activity
Break down by biological processes composting to carbon dioxide, water, inorganic compounds, and biomass
Break down in a similar time frame as naturals compostable materials such as cellulose
