Organic Chemistry

Question 1

What is the difference between a hazard and a risk?

Answer 1

A hazard is something that could cause harm to the user, whereas a risk is the chance of the hazard causing harm on the user.
In aqueous solutions you might have more than one hazard.

Question 2

What is a risk assessment?

Answer 2

It is a procedure carried out to identify the hazards in an experiment, assess the risks related and set control measures (guidelines) for it accordingly.

Question 3

Give examples of guidelines/control measures (precautionary measures).

Answer 3

Keep away from heat, gas produced so carry out in a fume cupboard, wear gloves, keep cap on bottle after using a substance, work on a smaller scale.

Question 4

Guidelines for apparatus

Answer 4

Mercury in thermometers is hazardous, use digital thermometer instead. Electric heating mantle instead of bunsen burner, tripod, gauze.

Question 5

Important rule/s for naming organic compounds

Answer 5

• Prefixes are written in alphabetical order

- Start numbering carbons in ascending order starting at the carbon closest to the functional group

Question 6

Define: oxidation, reduction, substitution, addition and polymerisation reactions

Answer 6

Oxidation- A species loses an electron
Reduction- A species gains an electron
Polymerisation- Where small molecules aka monomers are joined together to form a long chain of repeating monomers called polymer
Addition- Reactants combined to form one product
Substitution- Functional group is replaced by a diff one

Question 7

Types of bond breaking and define

Answer 7

Homolytic- Each atom gets equal no. of electrons from the bonded ones
Heterolytic- One atom takes all the bonding electrons

Question 8

Define free radical and electrophile

Answer 8

Free radicals are species that have an unpaired electron, they are highly reactive.
Electrophile is an electron acceptor and is attracted to areas of high electron density

Question 9

General formula of alkanes, alkenes, cycloalkanes, halogenoalkane, alcohol

Answer 9

CnH2n+2
CnH2n
CnH2n
CnH2n+1X
CnH2n+1

Question 10

Relate heterolytic fission to electrophiles

Answer 10

Heterolytic fission takes place when one of the atoms is more electronegative than the other, so it attracts the electron pair. That atom becomes a negative ion. The positive ion then becomes attracted to regions of high electron density. It will be labeled S+ and the high electron density region will be labeled S-. We use this in reaction mechanisms.

Question 11

Alkanes can be used as fuels. What three processes can be used to convert crude oil into fuels

Answer 11

Fractional distillation, cracking and reforming

Question 12

Name all the fractions in fractional distillation of crude oil.

Answer 12

Top to bottom: Refinery gas, Gasoline, Naptha, Kerosene, Diesel oil, Lubricating oil, Fuel oil, Bitumen

Question 13

Process of fractional distillation

Answer 13

Crude oil is vapourised then passed into the fractional column. There is a temperature gradient in the column, it gets cooler as you go up.

Question 14

Where are the compounds with larger molecules, long chains and higher boiling points found in the fractional column?

Answer 14

They are found at the bottom. They are also the most viscous.

Question 15

When does cracking take place and why

Answer 15

There is a high demand for hydrocarbons with shorter chains because they are better fuels and can be used to make polymers. There aren’t enough of them so we use cracking to make them from longer chains.

Question 16

Cracking conditions and process

Answer 16

Hydrocarbon is passed through a heated catalyst, usually zeolite. So conditions heat and catalyst.

Eg. decane broken down to octane and ethene. Ethene used to make polymers, octane used for petrol.

Question 17

Why reforming? Process and conditions.

Answer 17

Straight chained alkanes burn less efficiently and slower than branched ones. Reforming is used to turn straight chained alkanes into branched alkanes and cyclic hydrocarbons. Conditions are heat and a catalyst such as platinum.

They then burn more smoothly in the engine.
Eg. pentane gives cyclopentane and h2
heptane gives methylbenzene and h2

Question 18

Types of combustion of alkanes and their reactions

Answer 18

Complete- gives carbon dioxide and water.

Incomplete- gives carbon, carbon dioxide and water. This forms soot in a burner and can be seen as gas in the air as well.

Incomplete 2- gives carbon monoxide, a toxic gas which binds to haemoglobin in the blood and prevents transport of oxygen. Other products carbon dioxide and water.

Question 19

Explain the danger of the pollutants carbon monoxide and oxides of sulfur and nitrogen.
Also carbon dioxide.

Answer 19

Carbon monoxide- toxic gas. binds to haemoglobin to restrict oxygen transport in the blood. Leads to death.

Oxides of nitrogen and sulfur- rise up in the air and react with water to form sulfuric and nitric acid. Contribute to acid rain.

Carbon dioxide- Released with combustion, it is a greenhouse gas and causes global warming.

Question 20

Why do we need alternative fuels?

Answer 20

To reduce emissions of co2 and other pollutants.
Fossil fuels will run out or are depleted.
We need to reduce the effects of global warming and climate change.

Question 21

What are biofuels?

Answer 21

Fuels obtained from living matter that has died recently (rather than millions of years ago). Some biofuels are carbon neutral.

Question 22

Key things to focus on when comparing biofuels?

Answer 22

Yield- How much of fuel does it produce, how much can be grown or should be grown for good amount of the fuel
Land-How much land is required to grow the crop, should the land be used for other things?
Carbon neutrality- Is it carbon neutral?
Manufacture and transport- How much energy is used to grow, process and transport the crop?

Question 23

Compare biofuels to natural gas

Answer 23

Bio fuels use lots of land and it might replace land that is used to grow food whereas natural gas doesn’t require the use of land.

Biofuels have a low yield but it is gradually increasing. Natural gas has a very high yield.

No exploration or drilling costs for biofuels, but considerable costs for manufacturing and processing as well as transport. Natural gas high costs of exploration and drilling, low processing costs and low transportation costs because through pipelines.

Biofuels more carbon neutral. Natural gas is not carbon neutral at all.

Question 24

Conditions for chlorination of methane and what type of reaction is it

Answer 24

Substitution reaction. UV light needed.

Question 25

What type of bond breaking takes place in the halogenation of methane?

Answer 25

Homolytic fission. It happens in the initiation step to form 2 free radicals of the halogen.

Question 26

First and second step of halogenation? Write down their reactions.

Answer 26

Initiation- Homolytic bond fission to form 2 free radicals. Propagation- Free radicals react with stable molecules to form more free radicals. Use TB for written reactions.

Question 27

Last step of halogenation and write down the reactions.

Answer 27

Termination- Two free radicals react to form stable molecules. Use TB for reactions.

Question 28

Why can the yield sometimes be low for halogenation?

Answer 28

Because hydrogens are further substituted to form dichloromethane, trichloromethane and tetrachloromethane etc. Many of them will form instead of just chloromethane so the yield of chloromethane will be low.

Question 29

Explain the formation of the carbon-carbon double bond in alkenes.

Answer 29

After the three sigma bonds are made (1 C-C and 2 C-H bonds), there is one electron remaining in the p-orbitals of each carbon that is unbonded. These p orbitals on each carbon overlap vertically, creating regions of negative charge above and below the C=C double bond.

Question 30

# Define stereoisomerism. What is geometric isomerism as a branch of stereoisomerism?

Answer 30

When compounds have the same structural formula but are different in 3D arrangement. Geometric isomerism is when the atoms or groups of two compounds are attached at different positions on opposite sides of a C=C bond. So it has to be the same group/atom but attached on the other carbon and at different positions.

Question 31

What is E and Z?

Answer 31

E is trans and Z is cis. Cis means the groups are attached at the same position on the carbons. E means they're attached at diff positions on the carbons.

Question 32

Why does geometric isomerism only occur in alkenes and not alkanes?

Answer 32

This is because due to the presence of the C=C double bond in alkenes there is restricted rotation around the double bond. This allows for the groups attached to each C in C=C to only be in one of two possible positions. In alkanes, there is no double bond. This means the carbons and the attached hydrogens to them can rotate freely without restriction.

Question 33

Give the process and conditions for hydrogenation of alkenes.

Answer 33

Adding hydrogen to an alkene. Conditions are heat and a nickel catalyst.

Question 34

Describe what happens during addition reactions to alkenes.

Answer 34

Alkenes have a double bond. When a molecule is added to the alkene, pi-bond electrons are used to make new bonds with the attacking molecule. Eg. hydrogens will form bonds with the carbons using the pi-bond electrons. The pi-bond between the carbons is therefore broken and the bond becomes a single sigma bond. The product is more stable because it contains sigma bonds which are stronger than pi-bonds. Electrons in a pi-bond are more exposed to electrophilic attack because of the way the p orbitals overlap.

Question 35

Name the chemical test for a C=C double bond and its product and conditions.

Answer 35

Bromine gas or water test. Positive result: Decolourisation of bromine. Red-brown to colourless. Conditions: Away from sunlight. This is because alkanes will react with bromine by a free radical reaction in the presence of UV light/sunlight.

Question 36

Halogenation process and result? Give an example.

Answer 36

Halogen is added to an alkene. Forms a dihalogenoalkane. | Eg. dibromoethane with ethene and bromine

Question 37

Hydration process, product and conditions?

Answer 37

Adding steam to alkenes. H and OH are added. Product is an alchohol. Conditions are heat and acid catalyst.

Question 38

Addition of hydrogen halides process, product and conditions?

Answer 38

Adding a hydrogen halide eg. hydrogen chloride to an alkene. Forms mono-substituted halogenoalkanes. Eg. Ethene and HBr make bromoethane. This can't be used as a bromine test because the reactants are colourless as well.

Question 39

Describe oxidation of alkenes and give the product and conditions.

Answer 39

Double bond is oxidised and it forms a diol with two OH groups attached. Conditions acidified potassium manganate(VII). Product for ethene will be ethane-1,2-diol. Colour change observed purple to colourless.

Question 40

Describe the electrophilic addition of hydrogen halides to alkenes.

Answer 40

HBr and ethene example. Br is more electronegative than H and so there is a polarity difference. H S+ and Br S- form when the HBr molecule approaches the ethene double bond. Heterolytic fission takes place where the electrons in the HBr double bond both move to the Br S- atom. The electrons in the ethene double bond attract the H S+ atom. The hydrogen is now bonded to ethene. In a major product, the hydrogen will bond to the carbon that is bonded to less carbons/hydrogens. The Bromine is now a negative ion and a carbocation forms at the ethene. The opposite charges attract and Bromine bonds to the carbocation, forming the final product: Bromoethane. (not IUPAC name)

Question 41

Why is a Br2 molecule polar in electrophilic addition of halogens to ethene?

Answer 41

This is because as the Br2 molecule approaches the alkene double bond, the electrons in the double bond repel the electrons in the Br--Br bond inducing the molecule to become polar.

Question 42

Diff between minor and major product?

Answer 42

A major product is formed from the more stable carbocation, that is the one that has more electron releasing alkyl groups attached to the carbon. Minor product forms with the less stable carbocation, with less alkyl groups attached to it.

Question 43

When would an alkene have two possible products: minor/major?

Answer 43

When both the alkene and attacking molecule are asymmetrical. This means, for the alkene, that the atoms attached on either side of the double bond are different, and for the attacking molecule, that the two atoms are diff from each other. Ethene will have one possible product, but propene would have 2. That being said, it will only form 2 if the attacking molecule is a hydrogen halide because Br--Br or Cl--Cl are not asymmetrical.

Question 44

What are primary, secondary and tertiary carbocations and which is most stable?

Answer 44

Primary is only attached to one alkyl group. Secondary is attached to 2, and tertiary to 3. Tertiary forms the most stable products because it has more carbons to spread the charge over.

Question 45

Describe addition polymerisation of alkenes.

Answer 45

Alkenes are short-chained monomers which join together to form long chain polymers. The double bond is broken to form a repeating unit.

Question 46

Name two ways to limit problems caused by polymer disposal

Answer 46

Removal of the toxic gases released by incineration of polymers and production of biodegradable polymers.

Question 47

Give advantages and disadvantages of incineration as a way of polymer disposal.

Answer 47

Advantages: -Polymer waste can be converted into heat energy which can be used to generate electricity or for heating homes and factories. Disadvantage: -It releases carbon dioxide and toxic gases into the environment.

Question 48

Give advantages and disadvantages of producing biodegradable polymers.

Answer 48

Advantages: -They can be broken down by microbes in the environment which makes them easily disposable. Disadvantages: -They are made from plant material so land is needed to grow these plants, which can replace land used to grow plants for food. -When they break down, carbon and hydrogen atoms that remain cannot be directly used.