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HSC CHEMISTRYSUMMARY NOTESModule 5 - Equilibrium and Acid ReactionsIQ1: What happens when chemical reactions do not go through to completion?5.1. conduct practical investigations to analyse the reversibility of chemical reactionsDehydration of cobalt(II) chloride hydratesCo Cl 2 (s)+ 6 H 2 O(s)¿⇌Co ...

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HSC CHEMISTRY SUMMARY NOTES

Module 5 - Equilibrium and Acid Reactions IQ1: What happens when chemical reactions do not go through to completion? 5.1.1. conduct practical investigations to analyse the reversibility of chemical reactions Dehydration of cobalt(II) chloride hydrates

CoCl 2 ( s )+6 H 2 O (s) Co Cl2 ∙6 H 2 O(l) ⇌ ¿ pink Solid dehydrated cobalt(II) chloride is blue but when reacted with water, pink hydrated cobalt(II) chloride is produced. This reaction is reversible as when heated, the water evaporates and becomes blue again. Combustion of magnesium and steel wool Burning these two substances are both irreversible reactions as cooling will not reverse the reactions.

5.1.2 model static and dynamic equilibrium and analyse the differences between open and closed systems Dynamic and static equilibrium A dynamic equilibrium is when the rate of reaction is equal in the forward and reverse reaction. As such, the ratio between reactants and products remain unchanged. o It is dynamic as there is always movement of particles in both the forward and reverse reactions A static equilibrium is when the rate of reaction is equal and close to zero in the forward and reverse reaction. o There is no reaction in either direction once equilibrium has been reached and all particles in the system are at rest o An example is the conversion between graphite and diamond Open and closed systems In an open system, matter and energy can be exchanged with the surroundings. In a closed system, only matter can be exchanged with the surroundings. o Equilibrium can only be achieved in a closed system Answering model-type questions Understand what a model is for: o Simplify complex phenomena o Make predictions about future phenomena Advantages and disadvantages: o Generic advantage - makes it easier to understand

o Generic disadvantage - oversimplification o Specific advantages and disadvantages to the model Evaluation and justification as effective or ineffective

5.1.3 analyse examples of non-equilibrium systems in terms of the effect of entropy and enthalpy Enthalpy and entropy Enthalpy is the internal energy of a system, measured in J mol-1 or kJ mol-1 Only the change in enthalpy (ΔH) can be calculated. The standard formation is the ΔH associated with the formation of 1 mol of a substance in its standard state of 25°C and 100kPa from its constituent elements. The o The standard formation of an element at its standard state is 0kJ/mol If ΔH0, the reaction has a backward/reverse enthalpy drive - endothermic. Entropy is the measure of the state of disorder in a chemical system, measured in J mol-1 K-1 or kJ mol-1 K-1 Absolute entropy is always positive. The change in entropy (ΔS) is the difference in the sum of entropies of the products and the sum of entropies in the reactants. If ΔS>0, the reaction has a forward entropy drive. If ΔS103 the equilibrium position lies to the right o When K secondary > primary, in terms of basicity

−¿ ¿ RN H 2 (aq)+ H 2 O (l ) ⇌ RN H 3 ( aq)+ OH ( aq) Industrially, the alkylation of ammonia with alcohols is the most important method for the production of amines:

RO H ( aq ) + NH 3 ( aq ) → RNH 2( aq) +H 2 O( l ) Amides Amides contain a carbonyl functional group attached to a nitrogen atom. They are not basic. They are derived from carboxylic acids in which the -OH has been replaced by an amino group

7.5.5 investigate the structure and action of soaps and detergents Structure of soaps and detergents Soaps and detergents are surfactants designed to be more efficient at cleaning than water alone, as water is not good at dissolving non-polar substances, such as fats, oils and grease. Surfactants are substances which lower the surface tension of a liquid (the tendency of a liquid to decrease its surface area – consider a drop of water) The structure of a surfactant can be divided into two parts: hydrophilic head and hydrophobic tail. The chain length and cation influences the properties of a soap: o Longer chains with sodium heads make hard soaps

o

Shorter chains with potassium heads make semi-solid and liquid soaps

Soaps are compounds which are composed of a long hydrocarbon tail with a carboxylate ion (-COO-) head. However, they struggle in hard water, which contains Ca2+ and Mg2+ to form scum (solid precipitate). This precipitate reduces the efficacy of the soap and can leave undesirable marks behind (clothes-washing).

Detergents were developed to not form scum and be more effective in hard water, especially with the addition of phosphate builders. Anionic detergents o Negatively charged ion for the head o Often features a sulfonate group (-SO 3) o Quite harsh and cannot be used on human skin without irritation o Used in dishwasher detergents o Slightly less effective in hard water

Cationic detergents o Positively charged ion for the head o Usually features a quaternary ammonium o More expensive but less harsh o Used as hair conditioners and mouthwash o Not affected by hard water

Non-ionic detergents o Features repeating polyethylene glycol head o Uncharged but still polar o Less lather build-up than anionic detergents o Preferred in laundry detergents and are added in some shampoos and conditioners o Not affected by hard water

Action of soaps and detergents A surfactant molecules acts on the surface of a liquid, forming a monolayer.

If the surfactant molecule encounters a non-polar substance stuck onto a surface. 1. Surfactant comes into contact with grease or oil: o Hydrophilic head is attracted to water molecules, via hydrogen bonding o Hydrophobic tail interacts with grease and oil, via dispersion forces o Emulsion: two immiscible liquids coming together 2. With agitation, small droplets of grease or oil are lifted off the surface and momentarily suspends in water and micelles are formed 3. Micelles are established via repulsion forces between polar heads so that grease droplets do not mix together again 4. Micelles trapped with fat or grease can freely move through water and simultaneously be repelled from each other by the spherical outer surface

7.5.6 draft and construct flow charts to show reaction pathways for chemical synthesis

IQ6: What are the properties and uses of polymers? 7.6.1 model and compare the structure, properties and uses of addition polymers of ethylene and related monomers, for example polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS) and polytetrafluoroethylene (PTFE) Polymers Polymers are molecules composed of a large number of identical repeating subunits called monomers. Polymerisation is the process of linking monomers to form polymers. Plastics are any polymers than can be moulded via treatment: o Thermoplastics: polymers that can be moulded into the required shape continuously o Thermosetting plastics: polymers that are moulded when they are first made Properties of polymers Crystallinity

Branching

Chain length Side groups Cross-linking

Degree of structural order, achieved by compact polymer chains o Greater IMF o Characterised by high MP, opacity, rigidity Secondary polymer chains linked to the primary backbone o Weaker IMF between chains = low density, rigid, more flexible Measure of average number of monomer units per chain o More chain lengths = higher MP, more rigid Affects ability of the china to flex and move o Larger side group = less flexible Occurs when chains are connected in two or three dimensions o Greater cross-links = more rigid

Addition polymerisation Addition polymerisation involves sequential addition reactions of an unsaturated or reactive monomer to form a polymer that retains all molecules. Addition polymers are most commonly found in synthetic polymers formed from ethylene and its derivatives.

Low density polyethylene (LDPE) - plastic shopping bags, food packaging, plastic cling-wrap, electrical insulation o o

Produced in high temperatures and extremely high pressures Under these harsh conditions, the polymer is formed too rapidly for the molecules to be neat and symmetrical.

o o

o

Chemically unreactive: saturated C-H and C-C bonds Electrical insulator: no free charge carriers present in the structure Soft and flexible: branched polymer chains prevent the tight

o o

o

packing of individual molecules, compromising rigidity Transparent: low degree of light scattering, Low melting point (80oC): weaker dispersion forces, arising from the branched nature of the molecule Non-toxic

High density polyethylene (HDPE) - chairs, kitchenware, pipes, containers o o

o

Produced in high temperatures and low pressures Produced using the Zeigler-Natta catalyst, avoiding the need for high pressures Features very few branches

o

o

o o

Chemically unreactive, electrical insulator and non-toxic, as per LDPE High rigidity: tight packing of linear, unbranched polymer molecules Opaque: higher degree of light scattering High MP: strong dispersion forces

Polyvinyl chloride (PVC) - flexible tubing, rain coats, shower curtains, plastic furnishings, bank cards o

Formed when monomers of ethene with chlorine atoms in place of hydrogen atoms undergo addition polymerisation

o o o o

o

Rigid: linear chains with large Cl atom side groups Brittle: hard but breaks easily under tension Moderately resistant to chemical degradation High MP: presence of electronegative chlorine introduces dipoles  higher IMF Can add plasticisers to make resistant to UV

Polystyrene (PS) - CD cases, drinking classes, disposable cups, disposable plates o o

o

Addition reaction of styrene monomers Benzene rings are covalently bonded to every second carbon atom in the polymer chain Produced in both crystal and expanded forms – gas pumped (expanded is Styrofoam)

Crystalline o Rigid and hard o Impermeable to water Expanded o Lightweight o Heat insulator

Polytetrafluoroethylene (PTFE) - non-stick frypans, medical devices, other machinery o o

Formed from tetrafluoroethylene monomers Electronegative fluorine atoms reduce strength of IMF with other substances, affecting the properties of the polymer

o o o o

Rigid and durable Chemical unreactive Heat-resistant with high MP Non-stick and low-friction

7.6.2 model and compare the structure, properties and uses of condensation polymers, for example nylon and polyesters Condensation polymerisation Condensation polymerisation is the formation of polymers involving the production of some other small molecular product (water/ammonia). To successfully undergo condensation polymerisation, monomers with two functional groups (one at each end) are required. These must be capable of condensing out a small molecule when they react together. They may also occur between two different monomers (co-polymers), provided these monomers have compatible functional groups.

Common examples of condensation polymers include cellulose, starch, nylons, polyesters. Hence, o Additional polymers are formed when a number of the same monomer bonds together o Condensation polymers are formed when different monomers bond together in regular patterns

Nylon (polyamides) vs. polyesters Polyamines (nylon)

Polyesters (PET)

- firearms, guitar strings, machine parts -

- plastic bottles, food containers, frozen dinners -

o o

o o

Amide bonds link monomers together Di-carboxylic acid monomers polymerise with di-amine monomers Water is released H-bonding and dipole-dipole interactions exist

Structure:

o o

o o

Ester bonds link monomers together Di-carboxylic acid monomers polymerise with di-hydroxyl monomers Water is released Dipole-dipole interactions between chains only

Structure:

o o

Line or chain H-bonding

o o o

Properties: o High tensile strength o Ductile o Rigid o Resistant to thermal and chemical degradation

Long, crystalline chains Benzene ring Dipole-dipole forces and dispersion forces

Properties: o Colourless o Semi-crystalline o Resistant to water o High tensile strength o Virtually shatterproof

Specific comparison Name

Nylon

Polyest er

Structure

Properties Nylon is strong and elastic and is somewhat water resistant. It is strong, resilient, and heat resistant Polyester is a hydrophobic polymer that is very durable, chemical resistant, elastic and strong

Uses Nylon is used in clothing items such as stockings, elastics, socks, activewear, etc. Polyester is used in clothing items, such as polyester suits, shirts, pants etc. Polyester is also commonly used to make bottles

Module 8 - Applying Chemical Ideas IQ1: How are the ions present in the environment identified and measured? 8.1.1 analyse the need for monitoring the environment Contaminants in the environment Waterways o Still waterways: long-term accumulation of contaminants without opportunity for washout o Moving waterways: contaminants may be deposited in various areas far from the original source Soil o o

The soil supports a diverse range of organisms Contamination of soil  prevention of plant life growing, comprised ability to support thriving ecosystem

Atmosphere o Atmospheric pollution can cause rapid spreading of pollutants  affects health of organisms that respire Need for monitoring Monitoring is required to: o Prevent health consequences for organisms in the area o Prevent disruption of food chains and ecosystems o Ensure the air and water sources remain safe for human habitation Monitoring is important as: o The chance of pollution occurring is high o There are substantial consequences of pollution Chemical spills When chemicals (acids, bases, organic compounds) are spilt in the environment, it can cause harm. Spills can occur at the sight of production, during transportation, in storage or during use. e.g. pesticides may spill into nearby waterways and into the soil To minimise the risk of chemical spills: o Safety protocols must be in place strictly adhered to o Soil and water quality must be regularly monitored Fertilisers in waterways Fertilisers are a threat as: o They are frequently used in large quantities in agriculture o They contain high concentrations of nitrates and phosphates

Nitrates and phosphates accelerate the growth of algae (especially cyanobacteria) in water ways. This leads to eutrophication - the degradation of a waterway by the presence of excess plant life due to: o Dissolved oxygen may be depleted  unsuitable environment for remainder of the ecosystem o Dying/decomposing algae may accumulate  pristine waterways become swamps and marshes

Heavy metal ions in waterways Heavy metals are high density metals and when in high concentrations, they become harmful to humans and other organisms. They are found naturally dissolved in water sources, especially where water is exposed to the soil for long periods of time. These natural concentrations are usually insufficient to cause harm. Human activity can cause toxic increases in concentrations of heavy metal ions: o Industrial activity  release of contaminants o Waste materials being improperly disposed of into the environment o Combustion  atmospheric pollutants dissolve into water bodies Heavy metals can bioaccumulate and biomagnify, becoming a significant threat: o Bioaccumulation - the process by which substances build up in the tissues of a single organism o Biomagnification - process by which substance concentrations amplify up a food chain Heavy metal

Source Lead water pipes (e.g. corrosion) o Lead-acid batteries in cars which have been improperly disposed of o Atmospheric lead pollution o

Lead

o o Merc ury

Coppe r

o

o o o o

Mining Burning of fossil fuel Mercury-based products being produced or disposed of Digging from copper mines Copper-based paints Some pesticides Copper-piping

Health effects o o o o o

o o o o o o o o

Nausea and vomiting Acute and chronic confusion Chronic kidney disease Other neurological deficits Haematological compromises (anaemia) Nausea and vomiting Kidney disease Neurological deficits Inflammation of mouth and gums Gastrointestinal upset Liver failure Vomiting blood or rectal bleeding Anaemia

Environmental effects o

o

o

o

o

o o

Bioaccumulation and biomagnification Disruption in phytoplankton, disturbing aquatic ecosystem Soil dysfunction

Bioaccumulation and biomagnification Particularly builds up in apex aquatic organisms and avian predators Harmful to freshwater fish Soil contamination, damaging health of land-based

environment

8.1.2 conduct qualitative investigations - using flame tests, precipitation and complexation reactions as appropriate - to test for the presence in aqueous solution of ions listed Qualitative vs. quantitative testing for ions Qualitative testing involves identifying whether or not a specific ion is present, without determining the quantity present. (Is ion X present here?) Quantitative testing involves determining the precise quantity of a specific ion present. (How much of ion X is present here?) Flame tests In a flame test, aqueous transition metal ions are exposed to a flame, exciting electrons to high energy orbitals. o Transition metals (elements with a partially filled d-subshell) tend to absorb and release photos with frequencies that correspond to the visible light spectrum. o

ground state

input of photons →

excited state

output of photons →

ground state

Flame tests cannot be used for anions, as the photos released upon excitation and relaxation of their electrons fall outside the visible light spectrum. Some colours produced by various metal cations: Cation 2+

Barium (Ba ) Calcium (Ca2+) Magnesium (Mg2+) Lead(II) (Pb2+) Silver ion (Ag+) Copper(II) (Cu2+) Iron(II) (Fe2+) Iron(III) (Fe3+)

Flame colour Apple green Orange-red None Pale blue None Blue-green Green Orange-brown

Note: o The photons released in magnesium and silver lie outside the visible light spectrum and therefore do not produce a colour o A flame test is not usually performed for lead(II) ions as it is a neurotoxin

Precipitation reactions Precipitation reactions involve two solutions mixing together, resulting in the formation of a precipitate. o The insoluble solid may be present in clumps or as “cloudiness” in the mixed solution Whether or not a product salt is soluble or insoluble can be determined by applying the following solubility rules in order: 1. Group 1, nitrate, acetates are soluble 2. Silver, lead, mercury, copper salts are insoluble 3. Halides are soluble

4. Carbonates, sulphides, oxides, hydroxides, phosphates are insoluble 5. Sulfates are insoluble except calcium and barium Complexation reactions A complex ion is an ion which has a metal ion at its centre, surrounded by other attached ions or molecules. A complexation reaction is a chemical reaction that takes place between a metal ion and a ligand. Ligands are molecules/ions that are electron pair donors (Lewis base) and donate both electrons, to form coordinate covalent bonds. o It contains at least one atom with an unshared pair of electrons which it can donate to an empty orbital on the central metal cation to form a coordinate covalent bond o The most common ligands are water, ammonia, hydroxides, cyanides and chloride o The coordination number for a complex ion refers to the number of ligands tha...