Chapter 6 Flashcards
What is the general formula?
An algebraic formula that can describe any member of a family of compounds e.g. CnH2n+1
What is the empirical formula?
The simplest whole number ratio of atoms
What is the molecular formula?
The actual number of atoms of each element in a molecule
What is the structural formula?
Shows the arrangement of atoms carbon by carbon e.g. CH3CH2CH2OH
What is the skeletal formula?
Shows the bonds of carbon skeletal only. The hydrogen and carbon atoms aren’t shown
What does the displayed formula show?
How the atoms are arranged
What is nomenculture?
The naming of compounds
When there are 6 carbon atoms, what is the stem name?
Hex-
When there are 7 carbon atoms, what is the stem name?
Hept-
When there are 8 carbon atoms, what is the stem name?
Oct-
When there are 9 carbon atoms, what is the stem name?
Non-
When there are 10 carbon atoms, what is the stem name?
Dec-
If there’s more than one identical side-chain or functional group, what should you use?
Di-(2) Tri-(3) Tetra-(4)
What is a homologous series?
A bunch of organic compounds that have the same functional group and general formula
What is the suffix of alkanes?
-ane
What is the prefix of branched alkanes?
-alkyl
What is the suffix of alkene?
-ene
What is the prefix of halogenoalkanes?
Chloro/bromo/iodo -
What is the suffix of alcohols?
-ol
What is the suffix of aldehydes?
-al
What is the suffix of ketones?
-one
What is the prefix and suffix of cyclohexanes?
Cyclo- …. -ane
What is the suffix of carboxyclic acids?
-oic acids
What is an addition reaction?
Joining 2 or more molecules together to form a larger molecule
What is a polymerisation reaction?
Joining together lots of simple molecules to form a giant molecule
What is an elimination reaction?
When a small group of atoms breaks away from a larger molecule
What is a substitution reaction?
When one species is replaced by another
What is a hydrolysis reaction?
Splitting a molecule into 2 new molecules by adding H+ and OH- derived from water
What is an oxidation reaction?
A reaction in which species lose electrons
What is a reduction reaction?
A reaction in which a species gains electrons
What do curly arrows show?
How electron pairs move around
What are nucleophiles?
Electron pair donors, often negatively charged ions
As nucleophiles are electrons rich, what are they attracted to?
Areas that are electron poor, e.g. positive ions
What are electrophiles?
Electron pair acceptors, often positively charged ions
As electrophiles are electron poor, what are they attracted to?
Places that are electron rich, they like to react with negative ions, atoms with lone pairs
What do radicals have?
An unpaired electron
Why are radicals very reactive?
Because they have unpaired electrons, and radicals will react with anything, positive, negative or neutral
When are 2 molecules isomers?
If they have the same molecular formula but the atoms are arranged differently
What are the 2 main types of isomers?
Structural isomers and sterioisomers
What are the 3 types of structural isomers?
Chain isomers, Positional isomers, functional group isomers
What are chain isomers?
When the carbon skeleton can be arranged differently, e.g. as a branched or straight chain
What are positional isomers?
When the functional group is attached to a different carbon atom
What are functional group isomers?
When the same atoms can be arranged into different functional groups
What is the general formula of alkanes?
CnH2n+2
Alkanes are saturated, what does this mean?
All the carbon-carbon bonds are single bonds
What is heterolytic fission?
The bond breaks unevenly with one of the atoms receiving both of the electrons
What is homolytic fission?
The bond breaks evenly with each bonding atom recieving 1 electron, forming radicals
When halogens react with akanes, what do they form?
Halogenoalkanes
What are photochemical reactions?
Reactions that are started by light
When chlorine and methane react together, what are the 3 stages of the reaction mechanism?
- Initiation
- Propagation
- Termination
What happens in initiation reactions?
-Sunlight provides enough energy to break the Cl-Cl bond, the bond breaks evenly and radicals are formed
What is photodissociation?
When a chemical reaction is broken down by photons
What happens in the propagation reaction?
A radical Cl* attacks a methane molecule. The new methyl radical CH3 can attack a Cl2 molecule. The new Cl radical can attack another CH4 molecule until all the Cl2 or CH4 molecules are wiped out
What happens in the termination reaction?
Radicals are wiped out by reacting to form stable molecules e.g. Cl+Cl –> Cl2 CH3+Cl —> Ch3Cl
What are the main problems with when you react halogens with alkanes?
- You get a mixture of products
- You have to separate from unwanted products
- A mixture of structural isomers can be formed
What is petroleum?
Crude oil - sticky black stuff out of oil wells
What is crude oil a mixture of?
Hydrocarbons - mostly alkanes
How does fractional distillation work?
- Crude oil is vaporised at 350 C
- The vaporised crude oil goes into a fractionating column.
- As the crude oil vapour goes up the fractionating collumn, it gets cooler and the fractions are drawn off at different levels
In fractionating columns, why do the largest hydrocarbons form a residue at the bottom?
They don’t vaporise at all as their boiling points are too high
In crude oil, what can 5-12 carbons be used for?
Petrol
In crude oil, what can 11-15 carbons be used for?
Jet oil
What is ‘cracking’?
Breaking long chain alkanes into smaller hydrocarbons, which includes breaking the C-C bonds
What is thermal cracking?
Cracking at a high pressure and temperature which produces a lot of alkenes
What is catalyctic cracking?
Cracking which uses a zeolite catalyst and produces mostly aromatic hydrocarbons and motor fuels
What are aromatic hydrocarbons?
Compounds that contain a ring of 6 carbon atoms with a delocalised ring of electrons
What is knocking?
Where alkanes explode on their own accord when the fuel/air in the mixture is compressed
How do you make knocking less likely?
Adding branched chain and cyclic hydrocarbons to the petrol makes knocking less likely
Name 2 types of compound that are produced by reforming?
Cycloalkanes, branched alkanes
What happens when you burn alkanes in oxygen?
You get carbon dioxide and water
What is a combustion reaction?
When you burn alkanes in oxygen
What is incomplete combustion?
When there isn’t much oxygen around, so mainly carbon monoxide, carbon and water are produced
Why are alkanes excellent fuels?
Because they release so much energy when they burn
What is methane used for?
Central heating and cooking in homes
Why is carbon monoxide bad?
Carbon dioxide is better at binding to haemoglobin than oxygen, so less oxygen can be carried around the body
How does sulfur dioxide and nitrogen oxides lead to acid rain?
Sulfur burns to produce sulfur dioxide gas and then enters the atmosphere, dissolves in the moisture and is converted into sulfuric acid
What do catalyctic converters do?
They remove some pollutants from car emissions by using a platinum catalyst to change them into harmless gases, like water vapour and nitrogen or carbon dioxide.
What are biofuels made from?
Living matter over a short period of time
What is bioethonal?
Ethanol made from the fermentation of sugar from crops such as maize
What is biodiesel?
Made from refining renewable fats and oils such as vegetable oil
What is biogas?
Gas produced by the breakdown of organic waste matter
Why are biofuels classed as carbon neutral?
The produce the CO2 when burnt, but it is the same amount they absorbed while growing
What is the main problem from switching to biofuels in transport?
Petrol car engines would have to be modified to use fuels with high ethanol concentrations
What is the general formula of alkenes?
CnH2n
Why are alkenes unsaturated?
They can make more bonds with extra atoms in addition reactions
What are sigma bonds?
Single covalent bonds in organic molecles
When is a sigma bond formed?
When 2 orbitals overlap, in a straight line, in the space between two atoms
What does the high electron density in sigma bonds mean?
There is strong electrostatic attraction between the nuclei and the shared pair of electrons
Why are sigma bonds the strongest type of covalent bonds?
There is strong electrostatic attraction between the nuclei and shared pair of electrons so sigma bonds have high bond enthalpy
What is a double bond made up of?
A sigma bond and a pi-bond
When is a pi bond formed?
Two lobes of two orbitals overlap sideways
Why is the electrostatic attraction between the nuclei and shared pair of electrons weaker in pi bonds?
The elcectron density is spread out above and below the nuclei, so the elctrostatic attraction is weaker
In alkenes, what are all the C-C and C-H bonds?
Sigma bonds
In alkenes what are all the C=C bonds?
Sigma and pi bonds
As all the carbon atoms in a C=C double bonds and the atoms bonded to them are in the same plane, what does this mean?
All the angles are the same
Why can’t atoms rotate round a C=C bond?
Because of the way the p-orbitals overlap to form a pi-bond
What are sterioisomers?
Compounds that have the same structural formula, but different arrangement in space
Why can alkenes have sterioisomers?
Because of the lack of rotation around the double bond
When do sterioisomers occur?
When the two double-bonded carbon atoms each have 2 different groups attached to them
What does the Z isomer have?
The same groups either both above or both below the double bond
What does the E isomer have?
The same groups positioned across the double bond. E=opposite
How do you work out which is the Z isomer, and which is the E isomer for any alkene?
- The atom with the higher atomic number is given priority.
- When looking at the isomer, see how the groups of the same priority are arranged
What does ‘cis’ mean?
The same groups on the same side of the double bond
What does ‘trans’ mean?
The same groups on opposite sides of the double bond
When doesn’t the cis/trans naming system work?
When the carbon atoms have different functional groups attached to them so there is no way of deciding which is cis and which is trans
What happens to alkenes in an electrophillic addition reaction?
The alkene double bond opens up and atoms are added to the carbon atoms
Why do electrophillic addition reactions happen to alkenes?
The double bond has got plenty of electrons so is easily attacked by electrophiles
What are electrophiles usually?
Positively charged ions and polar molecules
What happens when you add hydrogen to C=C bonds? What are the reaction conditions?
They produce alkanes. It required a nickel catalyst and a temperature of 150 C
When halogens react with alkanes, what do they form?
Dihalogenoalkanes
When you shake an alkene with brown bromine water, what happens?
The solution quickly decoulorises
Why does the solution decoulorise when you shake an alkene with bromine?
Because dibromoalkane is a colourless solution
How can you manufacture ethanol from ethene?
Alkenes can be hydrated by steam at 300 C and a pressure of 60 atm to form ethanol. A solid phosphoric acid catalyst is required for the reaction
What is a diol?
An alcohol with 2 -OH groups
If you shake an alkene with acidified potassium manganate, what happens to the purple solution?
It is decoulorised, as you’ve oxidised the alkene and made it a diol
When alkenes undergo addition reaction with hydrogen halides, what is formed?
Halogenoalkanes
What does primary carbocation mean?
1 alkyl group
What does tertiary carbocation mean?
3 alkly groups attached to the carbon
Why are carbocations with more alkyl groups more stable?
Because the alkyl groups feed electrons towards the positive charge
Which carbocation is most likely to attract a bromine atom out of a primary and secondary carbocation?
A secondary carbocation as it is more stable
What can the double bond in alkenes open up and join together to make?
Long chains called polymers
What is addition polymerisation?
When alkenes open up their double bonds and join together to form a polymer
How do you find the monomer used to make a polymer?
Take the repeat unit, add a double bond between the carbons
What are the 3 main ways of disposing of polymers?
Burying them, reusing them, burning them
When is landfill used?
-When the plastic is difficult to separate from other waste, too difficult to recycle
How do you reuse waste plastics?
- melting and remoulding them
- cracking them into monomers
How do you burn waste plastics to get electricity?
Heat can be used to generate electricity, however toxic gases can be released, which is why waste gases are passed through scrubbers which can neutralise gases
How should a polymer be designed? (2 main factors)
To minimise the impact on human health and the environment
What are the set of principles that chemists must follow when designing a sustainable polymer manufacturing process?
- Use reactant molecules that are safe and environmentally friendly
- Renewable materials
- Energy use should be kept at a minimum
- Limit waste products
- Make sure lifespan of polymer is appropriate
What are the advantages of using renewable materials?
- Don’t run out
- When they biodegrade, if the polymer is plant based it will release the same amount of CO2 as it has absorbed
- Save energy
What sort of materials can biodegradable polymers be made from?
Starch, oil fractions such as isoprene
What is the purpose of scrubbers?
To neutralise gases, by allowing them to react with a base
What are halogenoalkanes?
Alkanes with halogen atoms
What is a primary halogenoalkane?
Where there is one alkyl group and 2 hydrogen atoms
What is a tertiary halogenoalkane?
Where there is no hydrogen atoms and 3 alkyl groups
How can halogenoalkanes be hydrolysed to alcohols?
By reacting them with water
When bromoethane reacts with water, what is formed?
Ethanol + H+ + Br-
When you mix a halogenoalkane with water and an alcohol is formed, why would you also want to put silver nitrate in the solution also?
The silver ions will react with the halide ions, giving a silver nitrate precipitate
Describe an experiment where you can compare the reactivities of halogenoalkanes using experiments?
- Set up 3 test tubes containing a different halogenoalkanes, ethanol and silver nitrate solution
- Time how long it takes for a precipitate to form in each test tube
What solution forms a precipitate faster out of a primary and tertiary halogenoalkanes?
Tertiary halogenoalkanes
In order to hydrolyse a halogenoalkane, what do you need to break?
The carbon-halogen bond
What reacts faster, a halogenoalkane with a a weaker carbon-halogen bond or a stronger carbon-halogen bond?
A halogenoalkane with a weaker carbon-halogen bond
Which halogen has the stronger C-X bond and which has the weakest C-X bond?
C-F is the strongest bond and C-I is the weakest bond
Which halogen is the most reactive halogenoalkane?
Iodine, as the C-I bond is the weakest bond
Why is the carbon-halogen bond polar?
Because the halogen atom is slightly more electronegative than the carbon atom
What is nucleophillic substitution in respect to halogenoalkanes?
A nucleophile bonds with the carbon atom in the halogenoalkanes and is substituted for the halogen
What happens when halogenoalkanes react with aqueous KOH?
An alcohol is formed (ROH) +KX
If you reflux a halogenoalkane with potassium cyanide in ethanol, what happens?
A nitrile is formed
What is a nitrile?
C=- N triple bond
When halogenoalkanes react with ammonia, what do they form?
Amines
What is an amine?
compounds that contain a nitrogen atom with a lone pair
If you warm a halogeoalkane with excess ethanolic ammonia, what happens?
The ammonia swaps place with the halogen
Once the ammonia has swapped place with the halogen, what happens next?
An ammoni molecule moves a hydrogen from the NH3 group to leave an amine
If you react a halogenoalkane with a warm alkali dissolved in ethanol, what do you get?
Alkene + Water + KX
When you react a halogenoalkane with a warm alkali dissolved in ethanol, what must the mixture be heated under?
Reflux
What is a primary alcohol?
An alcohol where the carbon the -OH is bonded to only connects to 1 other carbon
What is a tertiary alcohol?
An alcohol where the carbon the -OH is bonded to connects to 2 other carbons
What is PCl5?
Phosphorus pentachloride
If you react an alcohol with phosphorus pentachloride, what is produced?
A chloroalkane (RCl)
If you react an alcohol with hydrochloric acid, what is produced?
A chloroalkane (RCl)
When alcohols react with compounds containing bromide ions (e.g. KBr) in a substitution reaction, what can be formed?
A bromoalkane
How can you make iodoalkanes?
React an alcohol with phosphorus triiodide (PI3)
When alcohols are dehdrated, what do they form?
Alkenes
How do you dehdrate an alcohol?
Mix with an acid catalyst, and the alcohol will eliminate water
When butan-2-ol dehyddrates to form a mixture of products, what are the 3 possible isomer products?
But-1-ene E-but-2-ene Z-but-2-ene
What is the simplest way to oxidise alcohols?
Burn them ( complete combustion)
What are primary alcohols oxides to?
Aldehydes and then to carboxclic acids
What do secondary alcohols oxidise to?
Ketones only
WHat do teritary alcohols oxidises to?
Tertiary alcohols can’t be oxidised
What is an aldehyde?
Aldehydes have a hydrogen and one alkly attached to the carbonyl carbon atom
What is the carbon carbonyl atom?
C=O
What is a ketone?
Where there is 2 alkyl groups attached to the carbonyl carbon atom
When oxidising an alcohol, do you distil or reflux for an aldehyde, and do you distil or reflux to then get a carboxylic acid?
Distil for an aldehyde, reflux for a carboxylic acid
Do you reflux or distil to oxides a secondary alcohol?
You reflux
What does refluxing involve?
Heating a mixture in a flask fitted with a vertical Liebig condenser - this continuously boils, evaporates and condenses the vapours and recycles them back into the flask
Why do you reflux?
To make sure that you don’t lose any volatile organic substances
Why do you use distillation?
To separate substances with different boiling points
How does distillation work?
- By gently heating a mixture in a distillation apparatus
- The substances will evaporate out of the mixture in order of increasing boiling point
- When the thermometer shows the temp is changing, change the flask as a different liquid is being delivered
When would you use the technique of separation?
If a product is insoluble in water you can use separation to remove any impurities that do dissolve in water e.g.salts
How does separation work?
- Pour the mixture into a separating funnel, and add water
- The organic layer and aqueous layer do not mix
- Open up the tap and run each layer off
How do you remove traces of water from a mixture?
- Add an anhydrous salt such as magnesium sulfate or calcium chloride
- The salt binds to any water present to become hydrated
- You can filter the mixture to remove the solid drying agent
