CHEMISTRY (YEAR 12) - Chapter 11, 12 and 13 (Module 4)

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What is a homologous series?
A series of organic compounds with the same functional group but successive members differing by CH2
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What is a functional group?
A group of atoms responsible for the characteristic reactions of a compound
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What is the system of naming organic compounds called?
Nomenclature
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What are hydrocarbons?
Compounds made up of molecules containing only hydrogen and carbon atoms.
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What are the three groups of hydrocarbons?
Aliphatic, Alicyclic, and Aromatic
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What are aliphatic hydrocarbons?
In which carbon atoms are joined in chains - branched or straight (unbranched) chains
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What are aromatic hydrocarbons?
Aromatic hydrocarbons have an benzene ring in the structure
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What are alicyclic hydrocarbons?
In which the carbon atoms are joined together in a ring structure but are not aromatic
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What are the three homologous series of aliphatic hydrocarbons?
Alkanes (single carbon-carbon bond), alkenes (double carbon-carbon bond), alkynes (triple carbon-carbon bond)
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What are the two types of alkanes?
Alkanes are aliphatic so they can be unbranched or branched
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Name the first ten members of the homologous series of alkanes
Methane, Ethane, Propane, Butane, Pentane, Hexane, Heptane, Octane, Nonane, Decane
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How does the naming of alkanes change when they become branched?
They have a prefix which detailed the side chains (alkyl group) attached to the main chain
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What do the stem, suffix and prefix of an organic compound detail?
Stem - details the main part of the name (given by the number of carbons in the parent chain), Suffix - identifies the most important functional group, Prefix - identifies the other functional groups/ carbon atoms (alkyl groups) they are attached to
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What is the general formula for the alkyl group?
C(n)H(2n+1)
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What rules are there to naming organic compounds using suffixes and prefixes?
Numbers must be used to indicate which carbon atom the functional group/alkyl group is joined to, commas seperate number, dashes separate numbers and words, and prefixes must be written in alphabetical order.
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For organic compounds with more than one identical group what should be added?
A prefix before the prefix must be added - namely 'di' 'tri' or 'tetra'
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Sophie is naming an an organic compound, which contains the functional group of alcohols. Sophie names it butane-2-ol. Explain why Sophie is wrong.
To help with pronunciation, if the suffix starts with a vowel the final 'e' from the alkane part of the name is removed, so the cmpound would be butan-2-ol
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What is the formula, prefix and suffix for the functional group of alcohols
-OH, prefix hydroxy-, suffix -ol
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What is the formula and suffix for the functional group of aldehydes?
-CHO, suffix -al
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What is the formula and suffix for the functional group of alkanes?
C-C, suffix -ane
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What is the formula and suffix for the functional group of alkenes?
C=C, suffix -ene
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What is the formula and suffix for the functional group of carboxylic acids?
-COOH, suffix -oic acid
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What is the formula and suffix for the functional group of haloalkanes?
F, Cl, Br, I, suffixes fluoro-, chloro-, bromo-, iodo-
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What is the formula and suffix for the functional group of ketone?
C-CO-C, suffix -one
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What is the difference between a saturated and an unsaturated hydrocarbon?
Unstaturated hydrocarbons contain double carbon bonds and therefore don't contain the maximum number of hydrogen they could. Saturated hydrocarbons contain only single carbon-carbon bonds and therefore contain all the hydrogens possible
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What is a general formula?
All the compounds in a homologous series share the same general formula, it is like a 'rule' for generating the molecular formula of individual compounds
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What is a displayed formula?
A displayed formula shows the relative position of all the atoms in a molecule and all the bonds between them
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True or false "In the displayed formula of propanol, the functional group of alcohols is written -OH"
False, ALL bonds are shown in the displayed formula so it should be written -O-H
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What is a structural formula?
A structural formula gives minimum detail about the arrangement of atoms in a molecule
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What is an emperical formula?
The simplest whole-number ratio of atoms of each element in a compound
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What is a molecular formula?
The exact number of atoms of each element in a compound.
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What is a skeletal formula?
A simplified structural formula diagram showing briefly the arrangement and functional groups of a compound (hydrogen atoms removed)
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How is skeletal formulae drawn?
A new direction is taken for alyl chain between carbons, so every vertex is a carbon atom, including the end of the chain. Double bonds are shown as two lines. Functional groups are drawn from the vertices using a line and their formula.
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What are isomers?
Isomers are organic compounds that have the same molecular formula but different arrangements of their atoms
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What are structural isomers?
Structural isomers are compounds with the same molecular formula but different structural formulae
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What are the three types of structural isomers?
Chain isomers, functional group isomers and position isomers
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What is chain isomerism?
Chain isomerism is when there is a difference in the arrangement of the carbon skeleton (ie. branched or unbranched carbon chains)
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What is functional group isomerism?
Functional group isomerism are where the arrangement of atoms gives the molecule a different functional group
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What is position isomerism?
Position isomerism is when there is a difference in the position of the same functional group within the molecule
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What is stereoisomerism?
When organic compounds have the same molecular and structural formula but a different arrangement in space
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Name the two types of stereoisomerism
Geometric or E/Z isomerism and optical isomerism
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What is E/Z isomerism?
E/Z isomerism is the different arrangement of substituents around a double carbon bond with limited rotation
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How can you tell if an isomer is E or Z?
If the highest priority substituents are on the same side, the isomer is Z, if they are on opposite sides the isomer is E
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How can you tell which substituent on a caron is higher priority ?
By looking at the relative atomic mass of the atom the carbon is bonded to
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What is cis-trans isomerism?
A type of E/Z isomerism where one substituent groups on either side of the carbon are the same
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TRUE OR FALSE: A trans isomer is always a an E isomer
False, the substituents that are 'opposite' eachother may not be the highest priority for each carbon (see Br,Cl C=C Cl, C)
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If a cis-trans isomer is an Z-isomer is it cis or trans?
Cis isomer (same groups are parallel to eachother)
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What is the criteria for stereoisomerism?
1. Must have a double carbon-carbon bond (limited rotation) 2. Each carbon must have two DIFFERENT substituents attached
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What are the three homologous series of aliphatic hydrocarbons?
Alkanes (single carbon-carbon bond), alkenes (double carbon-carbon bond), alkynes (triple carbon-carbon bond)
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What is homolytic fission?
When a covalent bond breaks each electron does to a different bonded atom.
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What are the products of homoloytic fission called?
Free radicals (highly reactive, neutral species)
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What is the definition of a free radical?
A species with an unpaired electron
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How can homolytic fission be shown in an equation?
X-Y -> X• + Y•
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What is heterolytic fission?
When a covalent bond breaks, both electrons go to the same bonded atom
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What are the products of heterolytic fission?
An anion and a cation
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Why do alkanes have a low reactivity with many reagents?
The covalent bonds within alkanes are very strong and have high bond enthalpies also the carbon-hydrogenδ− bonds have such low polarity they are considered non-polar
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At what point does an alkane undergo complete combustion?
When there is a plentiful supply of oxygen
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Give the general word equation for complete combustion of alkanes
alkane + oxygen -> carbon dioxide + water
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Why does complete combustion give out the maximum amount of thermal energy possible?
The carbon and hydrogen in the alkane are fully oxidised
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At what point does an alkane undergo incomplete combustion?
When there is a limited supply of oxygen
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Name all the products that can be made during incomplete combustion of alkanes
Carbon dioxide, carbon monoxide, carbon (soot) and water
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What is the most common general word equation for incomplete combustion of alkanes
alkane + oxygen -> carbon monoxide + carbon + water
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What order should combustion reactions be balanced in?
C, H, O ( remember Miss Hockaday's rules initials CHO)
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What is the reaction mechanism for the production of haloalkanes for alkanes called?
Radical substitution
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What conditions must there be for the radical substitution reactions of alkanes?
UV lights and high temperatures (300 degrees Celsius)
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Describe briefly what happens during the radical substitution of alkanes
A hydrogen atom in an alkane is substituted by a radical halogen atom
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What are the three stages of the radical substition mechanism?
Initiation, propagation, termination
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What happens during initiation?
Radicals form from the diatomic molecules of the halogens through homolytic fission
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What happens during propagation?
A two step chain reaction that builds up the desired products
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What happens during termination?
Two radicals collide and make a stable product
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What is further substitution? How long can this continue?
If the reaction conditions are maintained, the chain reaction from the propagation stage continues but with a halogen replacing a hydrogen atom each time the cycle repeats. This can continue till all the hydrogen atoms have been substituted.
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How many reactions are there in each stage of the radical substitution mechanism?
Initiation: 1 Propagation: 2 Termination: 3
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Benny says "Propagation will only stop when all reactants have been used up." Explain why Benny is wrong
Propagation doesn't only stop when all the original reactants have been used up, termination often stops propagation as when the two reactants collide they are both removed from the reaction mixture
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Why does the Cl• radical in the first propagation stage not pull the whole alkane molecule to it?
It is not strong enough to pull the whole molecule and can only pull one hydrogen out of the molecule
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Why can the propagation stage of radical substitution give us isomers?
The propagation stage can give us several mono-substituted position isomers, where the mono-substituted halogen is in several places.
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Yasmin says "chain isomers have the same molecular mass so therefore must have the same boiling point." Explain why Yasmin is wrong.
Chain isomers do have the same molecular mass and thus the same number of electrons, however the more branched an isomer, the less surface area contact there is between molecules as they fit together less neatly and thus have weaker London forces.
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Explain why pentane has a higher boiling point than branched isomers of the same molecular mass
Pentane is a straight-chain isomer therefore Pentane molecules fit together more neatly than branched molecules and thus have more surface area contact between molecules. The stronger London forces require a greater amount of energy to overcome.
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What are the general properties of alkanes? What is the general formula of the alkanes?
Alkanes are saturated hydrocarbons (only single bonds) with very low reactivity. They have general formula CnH2n+2
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Name a use of alkanes
As fuels
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What are the covalent bonds between the carbons and hydrogen and carbons and carbons in an alkane called?
Sigma bonds
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How is a sigma bond formed?
A sigma bond is the result of a direct overlap between orbital of bonding atoms
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What is the shape around each carbon atom in an alkane? What is the bond angle?
Tetrahedral, bond angle 109.5
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Why do alkanes from butane onward not have a rigid shape?
The sigma bond in an alkane allow for free rotation (like an axes) after butane this means that an alkane can have several different shapes
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Why does a butane have a higher boiling point than ethane?
Butane is a longer carbon chain than ethane, which means that there are more points of surface area contact between adjacent molecules of butane. Therefore the London forces between molecules is greater and more energy is needed to overcome them.
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Why do structural isomers of alkanes have different boiling points, though they have the same molecular mass?
Less branched isomers fit together more neatly and therefore have more surface area interactions between molecules, thus the London forces between molecules is greater and more energy is needed to overcome them.
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What are the general properties of alkenes? What is the general formula for the alkenes?
Alkenes are unsaturated hydrocarbons (double carbon-carbon bonds) and are highly reactive. The general formula for the alkenes is CnH2n.
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For each carbon in a double bond how many electrons are used to make sigma bonds?
Three electrons, one sigma bond MUST go to the other carbon in the double bond
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What is a pi bond?
A pi bond is the the sideways overlap of adjacent p-orbitals above and below the bonding carbon atoms.
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A pi bond makes the double bond an electron dense area - where is this electron density concentrated?
Above or below the line joining the nulei of the two bonded atoms.
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True or false: "A pi bond between two atoms can form by itself"
False, a pi bond can only form after a sigma bond has already formed between the two atoms
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Which bond is stronger: Pi or Sigma?
Individual sigma bonds are stronger than individual pi bonds
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How does the Pi bond affect the shape of a molecule?
It locks the carbons in the double bond in place and restricts rotation around the double molecule
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What is the shape around each of the atoms in a double carbon-carbon bond?
The shape is trigonal planer
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Explain the shape and bond angles around each carbon in a double bond
There are three regions of electron density around each atom which repel each other equally, giving the molecule bond angles of 120 and each atom a trigonal planar shape. Due to pi bond restricting rotation the whole molecule is in the same plane
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What feature of alkenes causes them to be reactive?
The pi bond. The electrons in a pi bond are on the outside of the double bond (exposed) and create an area of electron density around the bond that attracts regeants. It is also weaker than a sigma bond and so is broken more readily
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What is the general formula for addition reactions of alkenes?
Unstaturated alkene + small molecule -> saturated molecule
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In the addition reactions of alkenes where is the small molecule added?
Across the double bond
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What is hydrogenation?
The reaction between hydrogen and an alkene, to produce an alkane
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What are the conditions for hydrogenation?
Nickel catalyst Ni, and temp 150 degrees
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What is halogenation?
The reaction between a diatomic halogen molecule and an alkene to produce a dihaloalkane
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What is the bromine water test for alkenes?
An alkene will discolour orange bromine water
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What is hydration of alkanes?
When an alkene is reacted with steam (H20) to form an alcohol
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What are the conditions for hydration of alkenes?
Phosphoric acid catalyst (H3PO4) temperatures of 300 degrees and pressure of 65 atm
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Jodie writes the hydration of ethene as C2H4 + H2O -> C2H5OH. Jodie is wrong. Why?
She has forgotten the (g) state symbol that indicates it is a reaction with steam and not water. Don't be like Jodie.
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What is the addition of hydrogen halides to alkenes?
When a hydrogen halide is added across the double bond (one hydrogen, one halide) to form a haloalkane
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Name two ways HCl, HBr or HI could be reacted with an alkene
HCl, HBr and HI are gases at room temperature so they can either be bubbled trhough liquid alkenes of mixed with gaseous alkenes
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What is the mechanism for the addition reactions of alkenes? Why?
Electrophillic addition reactions - the pi bond in a double carbon-carbon bond is an electron-rich area, which can attract electrophiles (*mostly* positive atoms/molecules attracted to electron dense areas and accept an electron pair)
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What is an electrophile?
An electrophile is an atom of a group of atoms attracted to an electron-rich area which will accept an electron pair. Generally have a positive charge or slight positive charge.
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What is a nucleophile
A nucleophile is an atom of a group of atoms that will donate an electron pair. They generally have a negative charge or slight negative charge.
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When showing the hydrogen halogen addition reactions of alkenes, which atom is attracted to the double bond? Why?
The hydrogen, because it is a polar molecule ( halogen more electronegative) making the hydrogen positively charged.
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When showing the halogenation of alkenes, which atom is attracted to the double bond? Why?
The one closest to the bond as this creates an induced dipole across the molecule (repels electrons) causing the atom closest to it to gain a slight positive charge.
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When showing the hydrogenation of alkenes, which atom is attracted to the double bond? Why?
The one closest to the bond as this creates an induced dipole across the molecule (repels electrons) causing the atom closest to it to gain a slight positive charge.
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When showing the hydration of alkenes, which atom is attracted to the double bond?
The H2O molecule is polar, with the OH being more electronegative and thus the hydrogen having a slight positive charge that means it is attracted to the double bond
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What type of fission takes place in the small molecule involved the addition reaction of alkenes?
Homolytic fission - one atom gets no electrons, the other atom gets both
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When the pi bond is broken, what is the carbon atom left unbonded called?
A carbocation (very reactive)
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What things must be shown in an electrophillic addition mechanism to gain marks?
The first two arrows must be drawn from the bond directly to the atom, in the direction of electron-transfer, the slight charges must be drawn over the small molecule. The last arrow must be drawn from the electrons to the charge on the carbocation
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What are the conditions for isometric products to be able to form?
An unsymmetrical alkene must bond with an unsymmetrical molecule.
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Which two electrophilic addition reactions can result in isometric products?
Addition of hydrogen halides and hydration of alkenes (unsymmetrical molecules)
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How is Markownikoff's rule used?
It is a rule that helps us to decide which of the isomeric products is the major and which is the minor product (i.e. which is produced more)
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What acrostic can be used to spell Markownikoff?
My Armanien Rotweiller Kayaks In Western Northumberland Incognito, Knowingly Overlooking Faraway Fiji
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What is Markownikoff's Rule?
A hydrogen will bond to the carbon atom with the most hydrogen atoms
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Why does the hydrogen bond to the carbon with the most number of hydrogens?
This leaves the halide/OH ion to bond with a more stable carbocation
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What is the stability of a carbocation determined by?
How many carbons it is attached to (including alkyl groups)
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What is a polymer?
A polymer is a large molecule made up of repeated units of monomers
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How do alkenes undergo addition polymerisation?
The pi bond breaks and the electrons used to make a sigma bond with the carbons of neighbouring molecules
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What things need to be remembered when drawing out the repeated unit of a polymer?
The repeat unit must be drawn in square brackets with an n outside and the lines representing the bonds must extend through the brackets.
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What is poly(ethene) used for?
Plastic bottles and bags
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What is poly(propene) used for?
Ropes and crates
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What is poly(chloroethene) used for?
Electrical cable insulation
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What is poly(phenylethene) used for? What is its other name?
Packaging and its other name is polystyrene
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What is poly(tetraflouroethene) used for?
Non-stick coating on cooking pans
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Name all six ways plastics can be disposed of?
Landfill, combustion, combustion with electricity, reusing, recycling, using them as organic feedstock
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Describe the problems associated with disposing of plastic waste through landfill
Plastics are not biodegradable, and so do not decompose in the ground. They can then become a danger to wildlife.
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Describe the problems associated with combusting disposed plastics
They contain large amounts of carbon, so release carbon dioxide when burnt. Carbon dioxide is a greenhouse gas (climate change). Other harmful chemicals like sulphur can cause acid rain.
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Describe the problems associated with recycling plastics
Separating plastics is expensive (machinery or labour-intensive) - not separated the usefulness of the process is undermined. Limited market - companies are concerned about the quality of plastics and contamination.
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What particularly are the issues with disposing of PVC?
It is neither biodegradable nor sustainably combustible, as it releases high amounts of hydrogen chloride which is corrosive as well as dioxines.
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What new way of recycling PVC is there?
Dissolving is with solvents and regaining high-grade PVC using precipitation.
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Describe the advantages of recycling
Conserves finite fossil fuels and reduces amount of plastics going into landfill
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What is feedstock recycling?
Using thermal and chemical processes to reclaim raw materials from disposed plastics that resemble the materials gleaned from fossil fuels.
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What are bioplastics?
Plastics produced from plant biomass (ie. plant oil, cellulose etc) or protiems
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What are biodegradable polymers?
Plastics that can be broken down - either these are made only from biodegradable polymers or traditional polymers with additives that mean they can be attacked by micro-organisms
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What are photodegradable polymers?
Oil-based polymers where either the bonds absorb sunlight or they contain additives that do. Once light is absorbed this weakens the structure and starts the breakdown of the polymers
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