HSC Trials Chemistry Notes (FULL) PDF

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HSC Chemistry Full Course Notes (HSC Mark 96)...

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Trial Chemistry Notes (FULL) Identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum Ethylene is one of the most important chemicals within the petrochemical industry and can be found natural in petroleum. However, within petroleum, there is only a small amount of naturally occurring ethylene, therefore the industrial source of ethylene is from the cracking of some of the fractions from the refining of petroleum. There are two ways to refining petroleum, thermal cracking and catalytic cracking. 1. Thermal cracking: The breaking down of larger hydrocarbons into hydrocarbons with a smaller molecular mass through the use of steam and heat. This usually is an expensive process, as it requires a lot of energy in order to be able to break the covalent bonds within the hydrocarbons. The heat needed is 700˚C to 900˚. Example: Ethene and propane from natural gas deposits 2. Catalytic cracking: The breaking down of hydrocarbon with larger molecular masses into hydrocarbon with lower molecular masses though the use of a catalyst called zeolite. Example: C18H38 4CH2=CH2 + C10H22

Identify that ethylene, because of the high reactivity of its double bond, is readily transformed into many useful products Ethylene contains a double bond, a double C=C bond within every ethylene compound as it belongs to the homogenous series of alkene. This double bond within ethylene allows the compound (and other alkene compounds) to undergo addition reactions. Addition reactions is a chemical reaction where the double bond of an alkene is broken and ‘opened up’ to allow other molecules to bond with the compound without any loss of other atoms or molecules. Therefore, ethylene are able to undergo addition reaction due to the high reactivity of the double bond present in ethylene. In ethylene, the double bond will react with other molecules due to its high reactivity, such as when two new atoms or molecules are added across the double bond, and hence breaking the double bond. When the double bond is broken, it allows the ethylene compound to have more bonding capacity and it will bond with other molecules, one new atom/molecule to each carbon atom that was linked by the double bond. This change the unsaturated ethylene compound that have a high reactivity double bond into a saturated compound. There are 4 types of addition reaction. 1. Hydrogenation When an alkene undergoes addition reaction where hydrogen atoms are added across the double bond, the alkene will be converted into an alkane. For example, ethylene is converted into ethane when ethylene is heated with hydrogen in the presence of a metal catalyst such as nickel, platinum or palladium. This is because, the double bond will be weaken by the metal catalyst, and reacts with the hydrogen atoms added, causing the double bond to break and hence bond with the hydrogen atoms. This will result into single covalent bonds present within the compound, all bonding hydrogen atoms to carbon atoms, thus being an ethane. Example: C2H4(g) + H2(g) C2H6(g)

2. Halogenation Halogenation is when halogens such as chlorine or bromine are added to alkenes. For example, when chlorine/bromine is added to ethylene, the double bond opens out and an addition reaction take places, forming a compound with the halogen. Also halogenation addition reactions are good for distinguishing between saturated and unsaturated hydrocarbon compounds. For example, when bromine solution with a distinct colour of red-brown is added to an alkene, it will lose it colours whilst when it is added to an alkane, it will retain its colour. Example: C2H4(g) +Br2(l) 1,2-dibromoethane(l)

When bromine is added to ethane, it was mentioned above that the red brown colour of the solution would be retain, which is a case where there is not chemical reaction between the bromine solution and ethane. However, if ultraviolet light is present, a chemical reaction will take place between bromine solution and ethane, although it is not an addition reaction. It would be a substitution reaction. 3. Hydrohalogenation Hydrohalogenation is when a compound with comprising of hydrogen and halogen is added to an alkene. For example, hydrogen chloride is added across ethylene’s double bond, where an addition reaction occurred. Example: C2H4(g) +HCl(aq) Chloroethane (l) 4. Hydration Hydration is an addition reaction where water is added to the alkene. For ethylene, hydration is an important addition reaction, as it would produce ethanol, an alcohol that has a potential for a fuel. Example: C2H4(g) +H2O(l) C2H5OH(l)

Identify that ethylene serves as a monomer from which polymers are made All substances can be a monomer or join together to form a polymer. A monomer is a small molecule, in which many can bond and join together to form a long chain. The long chain formed from identical small monomers joining together is a large molecule called a polymer. Ethylene is a monomer in which multiple identical ethylene compounds will bond together to form an ethylene polymer called polyethylene. As mentioned, ethylene is widely used in the petrochemical industry, in which one uses is that ethylene is the feedstock, starting chemical, in manufacturing polymers that can be used to produce various plastics. Factors that affects the properties of polymers: • The length of the chain – Longer chain length have more and greater dispersion forces between the chains, hence is stronger than the shorter chains • The degree of branching from chain – More branching within the chain will restrict the chain from having an orderly packed arrangement, reducing the density of the chain. Hence, more chain branching will lead to low density and high flexibility but less chain branching will lead to high density and hardness.

Identify polyethylene as an addition polymer and explain the meaning of this term Polymerisation is the chemical reactions by which monomers bond/link together to form a polymer consisting of identical repeating units. Ethylene will undergo polymerisation, and more specifically addition polymerisation, and produce polyethylene. Addition polymerisation is a process that involves breaking ethylene’s reactive double bond and providing each carbon atom with extra bonding capacity, allowing it to form more bonds between the monomers. Therefore, the monomers will then bond together and hence, a polymer (polyethylene) is formed. Thus, ethylene is an addition polymer, where an addition polymer is a large molecule formed from addition polymerisation of identical monomers bonding together due to the addition reactions across the double bond.

Outline the steps in the production of polyethylene as an example of a commercially and industrially important polymer There are three steps in the production of polyethylene. 1. Initiation Initiation is the first step in the production of polyethylene, where an initiator, usually a catalyst or a free radical (unpaired free electrons), will activate the ethylene molecule by breaking and opening up the reactive double bond present in ethylene. Furthermore, the initiator will bond with the activated ethylene molecules, forming an activated species. 2. Propagation The second step of the production of polyethylene is propagation. Propagation is where more ethylene monomers would bond together with the activated species and forming a growing chain with ethylene monomers adding to it each time. 3. Termination Termination involves two activated chains to randomly collide with one another, forming a bond and stopping the chain from growing any further. This will produce a stable polymer chain.

With the three main steps in the production of polyethylene, with different conditions will produce different types of polyethylene. There are two main types of polyethylene. 1. Low Density Polyethylene • High pressure • High Temperature • Requires a radical to initiate the polymerisation process • Properties: Stretchy, transparent, not very strong, malleable, flexible, non conductor • Low density polyethylene is flexible, stretchy and malleable due to its chain branching. In low density polyethylene, there are many chain branching due to the process used as it is produced. Hence, by decreasing the density of the polymer chains, the dispersion forces within the polymer chains is weaker as the chains cannot orderly pack together, giving the polymer chain flexibility. • Uses: o Low density polyethylene plastics is permeable to oxygen and carbon dioxide gases but not to water, therefore allows plastic flips such as cling wraps to keep food fresh and prevent the food from drying out. o Low density polyethylene is stretchy and light, therefore is used to produced plastic bags supplied by supermarkets o Low density polyethylene is also an electricity non-conductor and being flexible, it is used for the insulation of cables and wires 2. High Density Polyethylene • Low pressure • Low temperature • Requires a catalyst to initiate the polymerisation process • Properties: Hard, rigid, opaque strong, chemical resistance, malleable, durable • High density polyethylene doesn’t have any chain branching and hence, the polymer chain can orderly pack together. As the chains are orderly packed together, the dispersion forces within the polymers are closer and hence, are stronger, giving the polymer chains the property of hard and rigid (because breaking the strong dispersion forces between the polymer chains requires more energy). • Uses: o High-density polyethylene is used to manufacture gas pipes to carry natural gases, as it is chemically resistant and hard. o High density polyethylene being malleable can also be molded into containers to hold detergent and acid. o Due to high density polyethylene’s durability and strong strength, it is used to manufacture toys for kids

Identify the following as commercially significant monomers:

– Vinyl chloride – Styrene by both their systematic and common names Monomer Common Name: Vinyl Chloride Monomer Systematic Name: Chloroethene Polymer Common Name: Polyvinyl chloride Polymer Systematic Name: Polychloroethene

Describe the uses of the polymers made from the above monomers in terms of their properties 1. Polyvinyl Chloride (Polychloroethene) Polyvinyl chloride (PVC) is the polymer of vinyl chloride (systematic name: chloroethene). It is a thermoplastics addition polymer (hence formed from the addition polymerisation process). It has the properties of hard and brittle but with the inclusion of additives, properties such as thermal stability and flexibility is included and allows PVC to be used for various functions. • Rigid – Allows PVC to be used as water pipes • Flexible – Allows PVC to be used as garden hose • Electrical insulator – Allows PVC to be used as a electrical conduit 2. Polystyrene (Polyethylbenzene) Polystyrene is the polymer of styrene (systematic name: Ethylbenzene). It is a plastic most commonly used in the form of Styrofoam. Blowing gas through liquid polystyrene where the foam will form and once cooled, it will produce Styrofoam. This gives Styrofoam the properties of lightweight and electrical non-conductor. It has the properties of hard, clear, brittle, and clear. • Clear – Allows polystyrene to be used as CD cases as it is clear, allowing the content to be seen • Styrofoam, lightweight – Allows polystyrene to be used as disposable, Styrofoam cups and plates • Low density – Allows polystyrene to be used as body boards and core of surfboards as the low density will allow the board to float.

Identify data, plan and perform a first-hand investigation to compare the reactivities of appropriate alkenes with the corresponding alkanes in bromine water Aim: To compare the reactivates of cyclohexene and cyclohexane in bromine water Equipment: Bottle A, Bottle B, bromine water, 2 test tubes, 10mL measuring cylinder, test tube rack, 2 corks Method: 1. Measure 5mL of solution from bottle A using the 10mL measuring cylinder and pour it into a test tube 2. Measure 2mL of bromine water using the measuring cylinder and pour it into the test tube containing the solution 3. Put the cork into the test tube 4. Holding the cork, thoroughly shake the test tube for 30 second 5. Observe and record the changes. If the bromine water decolourises, then the liquid in bottle A is a cyclohexene 6. Repeat step 1 – 5 for the liquid in bottle B 7. Repeat step 1 – 6, 2 more times for reliability Risk Assessment: Bromine water, cyclohexene and cyclohexane is toxic via all routes,

therefore to prevent direct inhalation, perform the experiment in a fume box or ventilate the room Results: Observation Colour change

Other observation seen when bromine water is added

Bottle A Red orange colour of bromine water changed to colourless decolourisation Two distinct layer produced ‘Bubbles’, clear and oily like layer at the bottom

Bottle B Red orange colour remained

Two distinct layer produced Red – orange layer at the bottom whilst the clear layer at the top

Analyse information from secondary sources such as computer simulations, molecular model kits or multimedia resources to model the polymerisation process Aim: To compare the reactivates of cyclohexene and cyclohexane in bromine water Equipment: Bottle A, Bottle B, bromine water, 2 test tubes, 10mL measuring cylinder, test tube rack, 2 corks Method: 1. Measure 5mL of solution from bottle A using the 10mL measuring cylinder and pour it into a test tube 2. Measure 2mL of bromine water using the measuring cylinder and pour it into the test tube containing the solution 3. Put the cork into the test tube 4. Holding the cork, thoroughly shake the test tube for 30 second 5. Observe and record the changes. If the bromine water decolourises, then the liquid in bottle A is a cyclohexene 6. Repeat step 1 – 5 for the liquid in bottle B 7. Repeat step 1 – 6, 2 more times for reliability Risk Assessment: Bromine water, cyclohexene and cyclohexane is toxic via all routes, therefore to prevent direct inhalation, perform the experiment in a fume box or ventilate the room Results: Observation Colour change

Other observation seen when bromine water is added

Bottle A Red orange colour of bromine water changed to colourless decolourisation Two distinct layer produced ‘Bubbles’, clear and oily like layer at the bottom

Bottle B Red orange colour remained

Two distinct layer produced Red – orange layer at the bottom whilst the clear layer at the top

Analyse information from secondary sources such as computer simulations, molecular model kits or multimedia resources to model the polymerisation process Discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry As mentioned above, petroleum is a non-renewable fossil fuels where non-renewable means that it is a source that cannot be quickly replenished and takes millions of years to form.

Therefore, being a non-renewable source, petroleum would run out and hence, vital chemical compounds that are used in the petrochemical industry are also affected. For example, ethylene is a vital compound presently obtained through the cracking of hydrocarbons from the petrochemical industry. Ethylene is one of the raw feedstock chemicals and is widely used to produce products such as plastics, fibres, fabrics, and medicines. However, with petroleum running out, ethylene will not be able to be obtained through the petrochemical industry in the future, thus an alternative source of compounds such as ethylene that is obtained from the present petrochemical industry is needed. These plastics produced are in a huge part of human life. Hence, the world is heavily reliant on the products manufactured in the petrochemical industry and requires alternative sources that are renewable and sustainable. Therefore, another source of ethylene can be obtained from the fermentation of cellulose, a biomass derived from plant materials. Biomass is the organic materials derived from living organisms including plants and animals materials. Biomass would be a good alternative source of compounds presently obtained from the petrochemical industry because biomass is a renewable source and are the major component in the biosphere containing the natural biopolymer cellulose.

Explain what is meant by a condensation polymer A condensation polymer is a polymer derived from the chemical process of condensation polymerisation. Condensation polymerisation is the chemical process in which two functional group, each belonging to a different molecule, or a molecule that contain two different functional group that will invert/rotate and align itself. Once the functional groups are aligned, they will react to form a bond between the two functional group. This chemical reactions occurs with the elimination of a small molecules, usually water. Condensation polymerisation is another chemical reaction that produces polymers, and usually, biopolymers are produced through condensation polymerisation such as cellulose. Example of a condensation polymer is cellulose, which is a biopolymer.

Describe the reaction involved when a condensation polymer is formed Cellulose is a biopolymer formed from condensation polymerisation. It is made out of glucose monomers. A molecule of -glucose will react with another glucose monomer where in the polymer, every second  - glucose monomer’s hydroxyl functional group will invert and align itself with the hydroxyl functional group of the first -glucose monomer. Once the hydroxyl functional group aligns, they will form a 1,4-glycosidic bond ( linkage) and eliminate a water molecule. n(C6H12O6)

(C6H10O5)n + nH 2O

Consequently, a condensation polymer is formed when condensation polymerisation occurs where there will be two monomers, each containing a functional group, or a monomer containing two different functional group will invert and align to react and form a bond. After the functional group bonds together, a water/small molecule will be eliminated, hence a condensation polymer is formed.

Describe the structure of cellulose and identify it as an example of a

condensation polymer found as a major component of biomass Cellulose is a polymer made from  - glucose monomers where between each monomer unit, there is a 1,4-glycosidic bond. Each -glucose monomer has a hexagonal shape where there is a hydroxyl functional group on the 4th carbon atom, alternating between the top and bottom position. Further complimenting the alternative position of the hydroxyl group, the hydrogen atoms also alternates in position starting with 1st carbon atom.

Cellulose is an example of a condensation polymer aforementioned but it is also an example of a biomass because it is an organic material derived from living organisms such as plants. Rather, it is a major component of biomass because cellulose is mostly found in plants material, where plants are one of the most abundant living organisms in the biosphere.

Identify that cellulose contains the basic carbon-chain structures needed to build petrochemicals and discuss its potential as a raw material As cellulose is a natural biopolymer made from repeating units of -glucose monomers, it contains the basic carbon chain structure, as there are 5 carbons as well as hydrogen atoms within the structure of -glucose molecule. This carbon chain structure within cellulose is essential in building petrochemicals, as the carbon chain is needed to build the raw feedstock of ethylene and ethanol. Cellulose has the potential as raw materials for the production of petrochemicals as it can be broken down and will be broken down in order to produce ethylene and ethanol. However, cellulose only has the potential to be a raw material due to the advantages and disadvantages Advantages Cellulose is a renewable and sustainable resource that can be easily replenished as it is a biomass that can be obtained through the cultivation of plants Plastics made from biopolymers like cellulose is biodegradable making it more environmentally friendly as that reduces the amoun...