VCE CHEMISTRY 3&4 REVISION LECTURE SPRING 2021

VCE CHEMISTRY 3&4

SPRING 2021

Presented by: Josh HamiltonCreated by: Jack Higgins

REVISION LECTURE

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QUESTIONS + RESOURCES

• Below the video you should all see a small box that says Questions. In there you can post a question which I will answer in dedicated answer times.

• Please note, I will answer the most upvoted questions, so if there is a question like yours already uploaded, please upvote that question rather than post it yourself ((:

• There should also be a resource spot where you can access these slides and links, these I will talk about at times throughout the lectureLECT

URE

PLAN

LECT

URE

PLAN

9:30 – 10:10

Something something something Le Chatelier?

10:10 - 10:2010:20 – 10:25

If you’ve forgotten redox its okay, oxidants happen ….

BREAK 1 + Questions and Promos

10:25 – 11:10

BREAK 2 + Questions and Promos11:10 – 11:20 11:20 – 11:25

11:25 – 11:50

The exam is 60% of your study score, make it count!

Come say hi and ask questions!

BLOCK 1:THERMOCHEM & EQUILIBRIA

BLOCK 2:REDOX & ORGANIC CHEM

BLOCK 3:ANALYTICAL CHEM

11:50 – 12:00Questions

WHO AM I

WHAT DO I NEED TO KNOW?

the one trick

examiners don’t

want you to

know!!!

guaranteed* to

boost your SS by

100%

WHAT DO I NEED TO KNOW? UNIT 3

FUELS ELECTROCHEMISTRYEQUILIBRIA– Fuel choices

– Definition of a fuel– Comparing different fuels,

advantages and disadvantages

– Fuel calculations– Thermochemical equations– Universal gas equation – Stoichiometric calculations

– Reaction rates– Collision theory– Maxwell-Boltzmann

distributions– Energy profile diagrams– Factors affecting rate

– Reaction extents– Understanding equilibrium

systems– Equilibrium constants and

reaction quotients– Le Chatelier’s principle– Concentration vs. time graphs

– Redox basics– Oxidation and reduction– Redox half equations and balancing

overall equations

– Galvanic cells– Energy transformation– Common design features (anode,

cathode, salt bridge etc.)– Understanding the EC series

– Fuel cells– Comparing to galvanic cells – Comparison against combustible fuels– Design features

– Electrolysis– General principles and structures – Using EC series to predict reactions – Stoichiometry and Faradays laws– Secondary cells

WHAT DO I NEED TO KNOW? UNIT 4

ORGANIC CHEM EXPERIMENTAL DESIGNFOOD CHEM

– Structure & Nomenclature– Isomerism – Structures of alkan/en/ynes, benzene,

haloalkanes, primary amines, primary amides, alcohols, carboxylic acids and esters.

– Naming (most) of the above molecules

– Properties and reactions– Trends in physical properties A whole

bunch of different organic reactions– Putting those reactions together to

form reaction pathways– Percentage yields and atom economy

– Analysis– Principles and applications of MS, IR,

NMR, chromatography and volumetric analysis.

– Using spectra to identify compounds

– Food molecules– Proteins – Carbs– Lipids – Vitamins

– Metabolism– Metabolism pathways– Enzyme function and

structure – Coenzymes– GI, lactose intolerance– Antioxidants

– Experimental things – Variables (independent vs dependent)– Writing scientific reports and their

structure (aim, hypothesis, method etc.)– Reliability vs validity – Errors – Identifying limitations of experiments

and suggesting improvements

TOPIC 1: FUELS

FUELSFUELSFUEL CHOICES OBTAINING ENERGY

FROM FUELSMainly memorisationFor some reason often not explained well by textbooks.Qualitative informationComparing advantages and disadvantages of various fuels

Mainly understanding

Requires lots of practice at doing calculationsQuantitative informationCalculating the amount of energy or pollution released from fuels

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A fuel is a substance that can be reacted with other substances (e.g. O2), leading to the release of energy that can be harnessed for a specific purpose.

• Wording is important – don’t say ‘fuels can be combusted’! What about batteries? What about nuclear fission?

• Explicitly stated on the study design that you need to know a definition for a fuel, so remember one!

WHAT IS A FUEL?FUELS

Definition:

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WHAT IS A FUEL?FUELS

A non-renewable resource cannot be replenished by natural processes within a relatively short period of time.

RENEWABLE NON-RENEWABLE

A renewable resource can be replenished by natural processes within a relatively short period of time (short period = human timescale).

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FOSSIL FUELSBIOFUELS

Fuels derived from living matter compressed underground for millions of years.

Derived from plant matter and can be produced at the same rate we consume it.

FOSSIL FUELS VS. BIOFUELS

Coal Coal seam gas (CSG)

Crude oil/PetroleumLiquefied Petroleum Gas (LPG)

FUELS

FOSSIL FUELS

Biogas Bioethanol

Biodiesel

BIOFUELSSpecifically, we need to be able to compare the fuels listed, with respect to:

Energy content

Renewability

Environmental impacts relating to sourcing and combustion

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FOSSIL FUELS VS. BIOFUELS FUELS

BIOGAS

~60%CH4

~32%CO2

~8%

Biogas is composed of mostly methane (~60%), a little bit of carbon dioxide (~32%) and trace amounts of N2, H2S, H2O and O2.

CH! g + O" g ⟶ CO" g + 2H"O(l)

Because it contains less methane than fossil fuel gases (e.g. CSG, which is ~96% CH4), it releases less energy.

Key point: Produced by the anaerobic bacterial decomposition of organic wastes.

Image credit: Wikipedia commons

Anaerobic bacteria

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BIOETHANOL

C#H$"O# aq ⟶ 2 C"H%OH aq + 2CO" aq

Often used for vehicle transport. If you’ve seen E10 fuel at petrol stations, this is a blend of 90% petrol, 10% bioethanol!

Key point: Produced by the fermentation of glucose by yeast.

glucose ethanol carbon dioxide

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BIODIESEL

Key point: Produced by using plant oils or animal fats (triglycerides) in a transesterification reaction.

𝑡𝑟𝑖𝑔𝑙𝑦𝑐𝑒𝑟𝑖𝑑𝑒 + 𝑚𝑒𝑡ℎ𝑎𝑛𝑜𝑙 ⟶ 𝑔lycerol + 𝑏𝑖𝑜𝑑𝑖𝑒𝑠𝑒𝑙

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FUELS SUMMARY FUELS

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Type of fuel Energy content (roughly) Combustion environmental effects Sourcing environmental effects

Crude oil/Petroleum -Petrol produces more CO and particulates than smaller, gaseous fossil fuels; larger molecules result in a lower amount of complete combustion.

-Potential oil spills damaging aquatic ecosystems-Large amounts of energy required to power an oil rig, of which is mostly sourced from GHG emitting fossil fuels. -Risk of explosion releasing GHG into atmosphere.

LPG (C3 – C4) See belowPetrol (C8-C12) ~47.9 MJ Kg-1 (octane)Kerosene (C10-C18) ~46.2 MJ Kg-1

Petrodiesel (C12-C20) ~48.0 MJ Kg-1 (more dense than petrol, more energy per litre.)

Liquified Petroleum Gas (LPG) (propane and butane)

~46.2 MJ Kg-1 -Burns ‘more cleanly’ than other liquid and solid fossil fuels, producing less particulates, less sulfur oxides, and less nitrogen oxides.

-See crude oil.

Coal seam gas (CSG) (96% methane, 2% CO2)

~55.6 MJ Kg-1 (methane) -Burns ‘more cleanly’ than other liquid and solid fossil fuels, producing less particulates, less sulfur oxides, and less nitrogen oxides.

-Minor habitat destruction and fragmentation.-Contamination of local underground aquifers/water table as a result of fracking.

Coal (impure lumps of C(s)) Brown coal: 30 MJ Kg-1

Black coal: 35 MJ Kg-1-Releases large amounts of particulates/ash. -Inefficient combustion and energy transformations results in larger amounts of GHG emissions.

-Major habitat destruction -Large amounts of energy required to extract coal.

FOSSIL FUELS

Note: VCAA does not require you to know specific energy content values, but you do need to how the relative energy content of different fuels.

FUELS SUMMARY FUELS

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BIOFUELSType of fuel Production Energy content Combustion environmental effects Sourcing environmental effectsBiodiesel/FAME(Fatty acid methyl esters)

Produced from the transesterification of triglycerides, using a hydroxide catalyst and methanol.

~41 MJ Kg-1 -May not produce SO2 depending on source. -Relatively low CO2 net emissions as CO2

consumed during growing of crops. -Burns more completely, reducing particulates.

-Requires intensive farming, which may lead to land degradation and competition with land meant for food. -Crops required large amounts of energy to grow, resulting in large amounts of CO2 emissions -Methanol required, which is usually made in an unrenewable fashion from fossil fuels.

Bioethanol(Ethanol)

Fermentation of glucose by yeast. Same structure as ethanol.

~29 MJ Kg-1 -Releases CO2 upon combustion. -Burns more completely than petrol, less unburnt hydrocarbon released. -Lower NOx emissions. -Fewer particulates formed. -Lower energy content means more has to be combusted.

-Requires large amounts land and crops that could otherwise be used for food production. -Growing crops requires large amounts of energy, most of which is sourced from fossil fuels. -Relatively carbon neutral.

Biogas(60% methane, 32% CO2, small amounts of nitrogen gas, hydrogen sulphide, oxygen and hydrogen)

Anaerobic decomposition of organic wastes in an anaerobic digester.

~34 MJ Kg-1 -Releases CO2, both in the combustion of CH4 and as a large fraction of biogas. -H2S is a toxic constituent.

-Utilises waste products that would otherwise go unused.-Gas leak may emit large amounts of CH4 into the atmosphere.

Note: VCAA does not require you to know specific energy content values, but you do need to how the relative energy content of different fuels.

FOSSIL FUELS VS. BIOFUELSFUELS

FOSSIL FUELS

ADVANTAGES ✔ DISADVANTAGES ✖High energy content

Easy to release energy from

Relatively easy to obtain

Extensive existing infrastructure

NOT RENEWABLE!

Emits large amounts of CO2, a potent green house gas. Release other toxic chemicals, such as nitrogen & sulfur oxides

Extraction extremely damaging to the environment

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FOSSIL FUELS VS. BIOFUELSFUELS

BIOFUELS

ADVANTAGES ✔ DISADVANTAGES ✖RENEWABLE! Relatively carbon neutral; CO2 released during combustion somewhat offset by CO2 used by plant to grow.Burn more cleanly than fossil fuels, less harmful chemicals released Easy to source material used for production, can be produced from crop waste.

Lower energy content than fossil fuels

Can be complicated and costly to produce; making fuel out of plants isn’t as simple as digging up fuel from the ground! Can require large amounts of water to grow crops. Fertile land required to grow crops for fuel, which may compete with land to grow food.

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BIODIESEL VS. PETRODIESELFUELS

• VCAA specifically state on the study design that they want students to be able to compare biodiesel and petrodiesel!

BIODIESEL PETRODIESEL

3

Produced via transesterification of waste oils

Stronger dipole – dipole bonding makes it more viscous, can clog fuel lines at low temps

Burns more cleanly than petrodiesel, producing less particulates and other toxic chemicals.

Extracted from crude oil.

Large hydrocarbon chains experience only weaker dispersion forces, less viscous.

Produces particulates and other toxic chemicals when combusted.

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• For this topic, VCAA are particularly keen to test your ability to comparefuels. So, when answering questions, make sure you actually compare!

Example question: With reference to chemical structure, compare the suitability of biodiesel and petrodiesel as fuels to power vehicles in cold climates.

No comparison: Petrodiesel only experiences weak dispersion force attractions. Thus it has a lower cloud point, making it more suitable for use at low temperatures.

Good comparison: While biodiesel experiences dipole – dipole attractions, petrodiesel only experiences weaker dispersion forces. Thus, petrodiesel has a lower cloud point than biodiesel, making it a more suitable fuel at low temperatures, as it is less likely to solidify and clog fuel lines.

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Source -Can be produced from waste fats and oils or purposely grown oils.-Produced through a transesterification reaction, involving a triglyceride warmed with methanol in a hydroxide catalyst, forming glycerol and FAME.-Equilibrium reaction.

-A constituent of crude oil, obtained through fractional distillation. -Non-renewable

Chemical Structure

-Fatty acid methyl esters. -C10-C15, 75% aliphatic, 25% aromatic hydrocarbons

Combustion Products

-Emits CO2, but has a net lower impact as CO2 has recently been consumed in the production of oils.-Emits no SO2.-Burns more completely and produces less particulates.

-Emits CO2

-Produces some SO2. -Emits particulates and unburned hydrocarbons.

Fuel line flow -Electronegative O atoms in biodiesel result in dipole-dipole bonding, increasing its viscosity. -Polar bonds also result in biodiesel being hydroscopic, which may increase corrosion of fuel lines, degradation of fuel and blockages of fuel lines.-Can gel at low temperatures, clogging fuel lines and hence inhibiting engine functioning.

-Lower viscosity and a lower cloud point. -Not hygroscopic. -Large, non-polar hydrocarbons, only bonded together by weak dispersion forces.

Environmental impacts of production

-Large amounts of biodiesel production requires dedicated farming of crops, using land and plants that could otherwise be food.-Large amounts of energy and resources required to cultivate crops. Much of this energy may come from GHG emitting fuels, increasing GHG production.

-Crude oil spills can significantly damage ecosystems.-Risk of fire and explosion, releasing large amounts of GHGs. -Significant emissions in refining.


3

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BIODIESEL PETRODIESEL

PRACTICE QUESTIONFUELS

26VCAA 2016 Q3

PRACTICE QUESTIONFUELS

27VCAA 2016 Q3

UNIVERSAL GAS EQUATION THER

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CHEM

ISTRY

• Often we’ll be given the volume of a gas at a certain temperature.• However, volumes aren’t really useful (we can’t do stoichiometry with it

usually), so we want to convert to an amount in mol.

𝑃𝑉 = 𝑛𝑅𝑇𝑃 = pressure (𝑘𝑃𝑎)𝑉 = volume (𝐿)𝑛 = amount in mole of gas (𝑚𝑜𝑙)𝑅 = universal gas constant (8.314 𝐽 𝐾!" 𝑚𝑜𝑙!")𝑇 = temperature (𝐾)

Note: By using this equation, we assume the gas follows ideal behaviour. Ask me during a break if you wanna talk about this :)

Key point: Make sure you use the correct units! Pay particular attention to temperature, this is often given in ℃!

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• For constant conditions, the volume occupied per mol of gas is constant.

• The volume taken up per mol of an ideal gas is known as the molar volume.

Where does this number come from?

MOLAR VOLUMES

24.8 L mol-1SLC

NOTE: In the older study design the Vm at SLC was 24.5, so if you’re doing old exams use this value.

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V! = 24.8 L mol"#

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MOLAR VOLUMES

𝑃 = 100 kPa𝑇 = 298 K𝑅 = 8.31 𝐽 𝐾!"𝑚𝑜𝑙!"

THER

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ISTRY

𝑛 =𝑉𝑉!

Formula in data booklet

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THERMOCHEMICAL EQUATIONS THER

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ISTRY

• To compare the amounts of energy released or absorbed by systems, we use the concept of enthalpy change/heat of reaction.

• For the scope of VCE chemistry, the best way to think about enthalpy change is that its just fancy way of saying how much energy is released or absorbed.

𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑦 𝑐ℎ𝑎𝑛𝑔𝑒 ∆𝐻 ≈ 𝑒𝑛𝑒𝑟𝑔𝑦 𝑐ℎ𝑎𝑛𝑔𝑒*

• Enthalpy change is represented by ∆𝐻.

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MO

CHEM

ISTRY

CH! g + O" g ⟶ CO" g + 2H"O l ∆𝐻 = −890 𝑘𝐽 𝑚𝑜𝑙#$

Energy(enthalpy)

Reaction progress

CH4, O2

CO2, H2O

𝐻!"#$%#&%'

𝐻(!)*+$%'

Δ𝐻

∆𝐻 < 0

Δ𝐻 = 𝐻!"#$%&'( − 𝐻")*&'*+'(

EXOTHERMIC REACTION

‘Releases energy’

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MO

CHEM

ISTRY

6CO" g + 6H"O l ⟶ C%H$"O% + 6O" ∆𝐻 = +2816 𝑘𝐽 𝑚𝑜𝑙#$

Energy(enthalpy)

Reaction progress

C6H12O6, O2

CO2, H2O

𝐻!"#$%#&%'

𝐻(!)*+$%'

Δ𝐻

∆𝐻 > 0

Δ𝐻 = 𝐻!"#$%&'( − 𝐻")*&'*+'(

ENDOTHERMIC REACTION

‘Consumes energy’

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MO

CHEM

ISTRY

∆𝐻 > 0

Δ𝐻 = 𝐻!"#$%&'( − 𝐻")*&'*+'(

ENDOTHERMIC REACTION

‘Consumes energy’

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∆𝐻 < 0

Δ𝐻 = 𝐻!"#$%&'( − 𝐻")*&'*+'(

EXOTHERMIC REACTION

‘Releases energy’

THERMOCHEMICAL EQUATIONS

7 molecules

2 molecules 4 molecules

6 molecules

3120 𝑘𝐽 of energy! } 6.02 ×10",times! =

If we do this reaction 1 mole times we release 3120 kJ of energy, but how much energy is released by the combustion of 1 mole of ethane?

THER

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• Thermochemical equations are made of two parts:

1. Chemical equation 2. Enthalpy change value

2C"H# g + 7O" g ⟶ 4CO" g + 6H"O l ∆𝐻 = −3120 𝑘𝐽 𝑚𝑜𝑙?$

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THERMOCHEMICAL EQUATIONS

• It follows that when we manipulate thermochemical equations, we should alter the ∆𝐻 as follows:

Multiply coefficients of equation ⇒ multiply ΔH 2C,H- g + 7O, g ⟶ 4CO, g + 6H,O l ∆𝐻 = −3120 𝑘𝐽 𝑚𝑜𝑙./

4C,H- g + 14O, g ⟶ 8CO, g + 12H,O l ∆𝐻 = −6240 𝑘𝐽 𝑚𝑜𝑙./

Reverse the equation ⇒ negate ΔH 6CO, g + 6H,O l ⟶ C-H/,O- + 6O, ∆𝐻 = +2816 𝑘𝐽 𝑚𝑜𝑙./

C-H/,O- + 6O, ⟶ 6CO, g + 6H,O l ∆𝐻 = −2816 𝑘𝐽 𝑚𝑜𝑙./

Add two equations ⇒ add their ΔH values!

THER

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CHEM

ISTRY I, 𝑙 → 𝐼, 𝑠 ∆𝐻 = −16 𝑘𝐽 𝑚𝑜𝑙./

I, 𝑠 → 𝐼, 𝑔 ∆𝐻 = +62 𝑘𝐽 𝑚𝑜𝑙./

I, 𝑙 → 𝐼, 𝑔 ∆𝐻 = +46 𝑘𝐽 𝑚𝑜𝑙./

+

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THER

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ISTRY THERMOCHEMICAL EQUATIONS

DON’T FORGET THE ∆𝐻 SIGN >:-[

Key point:

6CO" g + 6H"O l ⟶ C%H$"O% + 6O" ∆𝐻 = 2816 𝑘𝐽 𝑚𝑜𝑙#$

6CO" g + 6H"O l ⟶ C%H$"O% + 6O" ∆𝐻 = +2816 𝑘𝐽 𝑚𝑜𝑙#$

• You will lose marks if you forget and more importantly you’ll make me disappointed…

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HEAT OF COMBUSTION

VCAA Chemistry Data Booklet, Page 10

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HEAT OF COMBUSTION

• The heat of combustion of a fuel is the amount of energy released when a specified amount (1 mol, 1 g, etc.) of that fuel undergoes complete combustion.

• Heat of combustion is denoted by the symbol ∆𝐻%

• It is very similar to enthalpy change/heat of reaction/∆𝐻, but there are some subtle but key differences!

Hydrogen, H2(g) ΔHc = 282 kJ mol!"

Ethyne, C2H2(g) ΔHc = 1300 kJ mol!"

Butane, C4H10(l) ΔHc = 2880 kJ mol!"

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• One of the key differences between ∆H and ∆HB is what the ‘per mol’ part means in each!

2CH3OH l + 3O2 g → 2CO2 g + 4H2O g ΔH = −1452 kJ mol#$

However, from data book, we have ΔHc methanol = 726 kJ mol#$

HEAT OF COMBUSTION

∆H gives us the amount of release per mol of reaction

∆H$ gives us the amount of release per mol of fuel used

Key point: ∆H is linked to the equation, ∆H$ is linked to the fuel.

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HEAT OF COMBUSTION

Key point: Heat of combustion is defined to be a positive number!!! When writing it down, you do not need to include any sign! For example…

Δ𝐻C(𝑒𝑡ℎ𝑎𝑛𝑜𝑙) = 1360 𝑘𝐽 𝑚𝑜𝑙!"

C%H&OH l + 3O% g ⟶ 2CO% g + 3H%O(l) Δ𝐻 = −1360 𝑘𝐽 𝑚𝑜𝑙!"

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HEAT OF COMBUSTION

Key point: When writing thermochemical equations under SLC conditions, water should technically be shown in the liquid state.

C%H&OH l + 3O% g ⟶ 2CO% g + 3H%O(l) Δ𝐻 = −1360 𝑘𝐽 𝑚𝑜𝑙!"

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HEAT OF COMBUSTION

vs ΔH!ΔH‘per mol of reaction’ ‘per mol of fuel’

Needs a + or – sign Has no sign

Changes depending on reaction Always the same value

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• Okay cool cool cool, so we know all about how fuels each have a heat of combustion, but how can we figure these values out in the first place???

¯\_(ツ)_/¯

Answer:

H!OStay hydrated kiddos

Key point: We know exactly how much energy it takes to heat water. We use this knowledge to perform Calorimetry!

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CALORIMETRY

• This is how we relate the mass, temperature change, and flow of energy from a substance!

𝑞 = 𝑚𝑐Δ𝑇

CALORIMETRY

𝑞 = energy absorbed or released (warning: J, not kJ)𝑚 = mass of substance (g) (NOT VOLUME)

𝑐 = specific heat capacity of substance (J g-1 °C-1 or J g-1 K-1)Δ𝑇 = change in temperature of substance (°C or K)

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• We can use 𝑞 = 𝑚𝑐Δ𝑇 in combination with Δ𝐻 = DE

to find the enthalpy change of a reaction!

• Note that these formulas are given in your data booklet, no need to memorise!

CALORIMETRY THER

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Warning: VCAA will no longer accept that: 1 g = 1 mL

CALORIMETRY

If given the volume of water, must used density to calculate mass.

𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = FGHHIJKLFM

Now there is a bunch of slides after this on Calorimetry, since these are very much Unit 4 I have left them in but we will skip them for time (:

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TOPIC 2: RATES & EQUILIBRIA

RATES & EQUILIBRIA

REACTION RATES EQUILIRBIUM

How and why reactions occurWhy different reactions occur at different ratesHow we can change the rate of reaction

Irreversible vs. reversible reactions

Dynamic equilibrium and the extent of a reactionQuantifying the extent of a reaction (equilibrium constant)Calculations and predicting changes in equilibrium position

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RATES &

EQUILIBR

IA

• Chemical reactions are a result of collisions between molecules.

• However, not all collisions result in a reaction!• Collisions that result in reaction = successful (or ‘fruitful’)

Two main aspects determine whether a collision is successful:

COLLISION THEORY RATES &

EQUILIBR

IA

1. Collisions must be sufficiently energetic

2. Collisions must occur with correct orientation

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COLLISION THEORY

reactants

products

𝐸3= Activation energy

Δ𝐻

energy

reaction progress

RATES &

EQUILIBR

IA

1. Collisions must be sufficiently energetic:

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Energy of collision ≥ Activation energy

COLLISION THEORY

2. Collisions must occur with correct orientation:

RATES &

EQUILIBR

IA

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We are concerned with making reactions go faster. What can we do?There are two fundamental ways to increase reaction rate:

Method 1: Increase collision frequency• Higher temperature• Higher pressure and concentration• Higher surface area

Method 2: Increase the proportion of successful collisions• Higher temperature• Catalysis

As we will see, we can utilise both methods to increase reaction rate :)

RATES OF REACTION RATES &

EQUILIBR

IA

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Method 1: Increase collision frequency:Increase temperature

Increase concentration (solutes), pressure (gases)

Increase surface area (solids or surfaces)

Higher temp ⇒ faster movement of particles ⇒ higher collision frequency ⇒higher frequency of successful/fruitful collisions ⇒ higher reaction rate

More particles ⇒ more collisions ⇒ more successful/fruitful collisions ⇒higher reaction rate

Higher surface area ⇒ more ‘stuff’ to bump into ⇒ more collisions ⇒ more successful/fruitful collisions ⇒ higher reaction rate

RATES &

EQUILIBR

IA RATES OF REACTION

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Method 2: Increase proportion of successful collisions:

Increase temperature

• Higher temp ⇒ higher collision freq.• Higher temp ⇒ higher success rate (**)

Higher temp ⇒ particles move faster ⇒ have more energy ⇒ more collisions overcome EA

Key point: Increasing temperature affects reaction rate in both ways!

RATES &

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Use a catalyst

Method 2: Increase proportion of successful collisions:

Catalysts provide an alternative reaction pathway with lower activation energy (EA) that allows more collisions to succeedImportant: alternative reaction pathway – catalysts change the reaction mechanism!

RATES &

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reactants

products

𝐸#=activation energy

Δ𝐻

energy

reaction progressnon-catalysed pathwaycatalysed pathway

When you successfully catalyse your reaction and its now 1017 times faster

RATES &

EQUILIBR


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To summarise, 5 major factors:

• Surface area of solid reactants

• Concentration of reactants in solution

• Gas pressure

• Temperature

• Presence of catalysts

Be careful with these!

RATES &

EQUILIBR


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A mathematical model for the distribution of particle speeds that varies with temperature.• Shaded area represents number of particles with 𝐸 ≥ 𝐸P• Only collisions with energy above EA will be successful

MAXWELL-BOLTZMANN DISTRIBUTION

https://www.desmos.com/calculator/s2x18iawnh

RATES &

EQUILIBR

IA

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https://www.desmos.com/calculator/s2x18iawnh

MAXWELL-BOLTZMANN DISTRIBUTION RATES &

EQUILIBR

IA

EA

EA

EA

Increase in temp:

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MAXWELL-BOLTZMANN DISTRIBUTION RATES &

EQUILIBR

IA

EA

EA

EA

Use of catalyst:

66

• Rate of reaction:– How FAST the reaction occurs - how fast reactants are converted to products– In terms of equilibrium? How fast does it reach equilibrium

• Extent of reaction:– How FAR has the reaction gone – how much reactant has been converted to product– This is where equilibrium comes in!

RATE OF REACTION VS. EXTENT OF REACTION

Don’t mix these up!

RATES &

EQUILIBR

IA

67

• At equilibrium, the forward and reverse reactions exactly cancel each other out!!

• Chemical equilibrium is sometimes described as dynamic; even though it doesn’t look like any reaction is occurring, there is!

• No reaction appears to occur because the forwards and reverse reaction occur exactly at the same rate, meaning the amount of each doesn’t change.

EQUILIBRIUM RATES &

EQUILIBR

IA

68

EQUILIBRIUM RATES &

EQUILIBR

IA

Rate of forward reaction = rate of reverse reaction

Concentrations of chemicals don’t change!

69

EQUILIBRIUM CONSTANT RATES &

EQUILIBR

IA

70

N! g + O! g ⇌ 2NO(g)

Initial Equilibrium


EQUILIBR

IA

71

H! g + Br! g ⇌ 2HBr(g)

Initial Equilibrium

How do we quantify equilibrium and the extent of a reaction?

• The extent of a chemical reaction is described by its equilibrium constant (K).• We can think about what the value of K means by considering the following

‘generalised’ equation.

𝐾 =products &#),-.&.)+'(

reactants &#),-.&.)+'(

NQ g + OQ g ⇌ 2NO(g) K = 4.1 ×10!R" at 25 ℃HQ g + BrQ g ⇌ 2HBr(g) K = 1.9 ×10"S at 25 ℃


EQUILIBR

IA

72

Say we have some reaction….aA + bB ⇌ cC + dD

We define the equilibrium constant, K

K =C TUVB D TUV

W

A TUVX B TUV

Y

A TUV, … = concentration of A at equilibrium, so on

Like ΔH and E°, K values are associated with chemical equations.K depends only on temperature for a given reaction!!!


EQUILIBR

IA

73

Remember…

The equilibrium constant 𝐾 doesn’t depend on the starting conditions of reaction (reaction volume, concentration of reactants, etc.).

However, 𝐾 does depend on the reaction temperature.Example:

2NO2(g) ⇌ N2O4(g), ΔH = -57.1 kJ mol-1

What is the effect of ↑ temperature on the equilibrium constant?System wants to reduce temperature – favours endothermic reaction

EQUILIBRIUM CONSTANT

TEMPERATURE IS THE ONLY THING THAT CAN CHANGE THE K VALUE

Exothermic à

ß Endothermic

EQUILIBR

IA

In general..

Exothermic reactions:↑ temperature ⇒ ↓ 𝐊↓ temperature ⇒ ↑ 𝐊

Endothermic reactions:↑ temperature ⇒ ↑ 𝐊↓ temperature ⇒ ↓ 𝐊

EQUILIBRIUM CONSTANTEQ

UILIBRIA

• Reverse equation ⇒ 𝐾Z = "[

A + B ⇌ C + D K" =\ ]^ _

C + D ⇌ A + B KQ =^ _\ ] = "

`!• Double equation ⇒ square K

A + B ⇌ C + D 𝐾" =a bP c

2A + 2B ⇌ 2C + 2D 𝐾Q =a " b "

P " c " = 𝐾"Q


UILIBRIA

• Half equation ⇒ square root K

2A + 2B ⇌ 2C + 2D 𝐾Q =a " b "

P " c "

A + B ⇌ C + D 𝐾" =a bP c

= 𝐾Q


UILIBRIA

• Q is the reaction quotient– Calculated the same as K– Gives relationship between amount of reactant and amount of product at a given time

• K is the equilibrium quotient– Gives relationship between amount of reactant and amount of product at equilibrium– Q at equilibrium

• Q = deJfLCgHhMGCgGEgH

– If Q>K, it means there is too much product – must reduce product therefore shifts to the left– If Q<K, it means there is not enough product – must increase product therefore shifts to the

right– If Q=K we are at equilibrium – No change

CHEMICAL EQUILIBRIUMEQ

UILIBRIA

VCAA 2009

PRACTICE QUESTIONEQ

UILIBRIA

VCAA 2009

PRACTICE QUESTION

Q = [56]!

5! [6!]= [.9]!

.:, [.:/]= 800

Q>K – shifts to the left

EQUILIBR

IA

If a system in equilibrium is subject to a change, the system will respond to partially oppose that change.

• This is just a rule – it’s not the real reason why things work the way they do

• Can think of it in terms of Q and K

LE CHATELIER’S PRINCIPLEEQ

UILIBRIA

Numerical equilibrium problems..• Example: calculate the final equilibrium concentrations of species given…

• Initial concentrations of all species• Value of the equilibrium constant 𝐾• Equilibrium concentration of one species

Remember to use RICE tables…

CHEMICAL EQUILIBRIUMEQ

UILIBRIA

RICE tables…RICE (ratio, initial, change, equilibrium) tables are a very useful tool for solving equilibrium problems.

2NOCl(g) ⇌ 2NO(g) + Cl2(g)

CHEMICAL EQUILIBRIUM

R 2NOCl ⇌ 2NO Cl2I

C −2𝑥 +2𝑥 +𝑥E

EQUILIBR

IA

Consider the reactionCO(g) + 3H2(g) ⇌ CH4(g) + H2O(g), K = 0.67

Initially, 0.1 mol CO(g), 0.2 mol H2(g), 0.1 mol CH4(g) and 0.3 mol H2O(g) were added to a sealed 1.0L reaction vessel. At equilibrium, 0.032 mol CH4 was detected.

What were the equilibrium concentrations of the other species?


R ⇌I

C

E

EQUILIBR

IA

Consider the reactionCO(g) + 3H2(g) ⇌ CH4(g) + H2O(g), K = 0.67

Initially, 0.1 mol CO(g), 0.2 mol H2(g), 0.1 mol CH4(g) and 0.3 mol H2O(g) were added to a sealed 1.0L reaction vessel. At equilibrium, 0.032 mol CH4 was detected.

What were the equilibrium concentrations of the other species?


R CO 3H2 ⇌ CH4 H2O

I .1 .2 .1 .3

C + 0.068 + 3 x 0.068 - 0.068 - 0.068

E .168 .404 .032 .232

EQUILIBR

IA

VCAA 2008

PRACTICE QUESTIONEQ

UILIBRIA

VCAA 2008

PRACTICE QUESTIONEQ

UILIBRIA

88

PROMO

BLOCK 1: QUESTION

TIME

BREAK SLIDE

TOPIC 3: ELECTROCHEM

galvanic cell

electrolytic cell

REDOX BASICS ELECTRO

CHEM

ISTRY

Image credit: Wikipedia

OXIDATION REDUCTION

OIL RIGis loss of electrons𝑀 ⇌ 𝑀 + + 𝑒 −

is gain of electrons𝑀 + + 𝑒 − ⇌ 𝑀

92

• In a redox reaction, one species is the oxidant, and the other is the reductant.

Terminology matters…

The oxidant causes oxidation (of the reductant) and is itself reduced!The reductant causes reduction (of the oxidant) and is itself oxidised!

• Another way you can think about it, a teacher does the teaching, just like an oxidant does the oxidising.


CHEM

ISTRY

93

• So how can we determine if a reaction is redox? • We use oxidation numbers, also called oxidation states

OXIDATION STATES ELECTRO

CHEM

ISTRY

1) Pb"- aq + 2Cl#(aq) ⟶ PbCl"(s)

2) NaOH aq + HCl aq ⟶ NaCl aq + H"O(l)3) 2Al s + 3Cl" g ⟶ 2AlCl, s

94


CHEM

ISTRY

• There’s a few rules to remember! Hopefully you’re feeling comfortable with these!

1 Oxidation states of free elements (Fe, Na, ClQ, He etc. ) is 0. 0 0 0 0

2 Oxidation states of simple ions (Nak, Cl!, MgQk, NR!etc. ) is equal to the charge on that ion.

+1 − 1 + 2 − 3

3 In compounds:Main group metals have oxidation state equal to charge of their ions (NaCl, MgBr,)

+1 + 2

Hydrogen is almost always +1, and oxygen is almost always -2 (H,O)+1 − 2

Sum of all oxidation states must equal charge on species

+4CO,

+4 + 2(−2) = 0

+5 − 2

+5 + 4 −2 = −3

+1 − 2

3 +1 + −2 = +1

PO9 ;. H;O<−2

95


CHEM

ISTRY

1) Pb"- aq + 2Cl#(aq) ⟶ PbCl"(s)

2) NaOH aq + HCl aq ⟶ NaCl aq + H"O(l)

3) 2Al s + 3Cl" g ⟶ 2AlCl, s

A reaction will only be redox if two or more atoms have a change in oxidation states!

✖ Not redox :[

✖ Not redox :[

✔ Redox :D

If the oxidation state reduces then that species was reduced! (e.g. Cl goes from 0 to -1)

If the oxidation state increases then that species was oxidised! (e.g. Al goes from 0 to +3)

96

• How do we actually figure out the half equations though? D:• We use the KOHES method!

BALANCING HALF EQUATIONS ELECTRO

CHEM

ISTRY

K Balance the Key atoms – all atoms except H and O.

O Balance the Oxygen atoms – by adding HQO.

H Balance the Hydrogen atoms – by adding Hkions.

E

S

Balance charge – by adding Electrons 𝑒! .

Don’t forget States!

97

BALANCING HALF EQUATIONS• When using the KOHES method, we have been making an assumption; that

the reaction medium is acidic. • What happens if instead the reaction medium is basic/alkaline? We need an

extra step!

K Balance the Key atoms – all atoms except H and O.

O Balance the Oxygen atoms – by adding H%O.

H Balance the Hydrogen atoms – by adding H)ions.

E

S

Balance charge – by adding Electrons 𝑒! .

Don’t forget States!

H Cancel out the Hydrogen ions – by adding OH!ions.

ELECTRO

CHEM

ISTRY

98

GALVANIC CELLS ELECTRO

CHEM

ISTRY

We’ve all used galvanic cells before, they’re an essential part of life as we know it!

CHEMICAL ENERGY

ELECTRICAL ENERGY

Cell

} Battery

A galvanic cell is simply any device that converts chemical energy into electrical energy.

101

GALVANIC CELLS - TERMINOLOGY ELECTRO

CHEM

ISTRY

102

GALVANIC CELLS – EXAMPLE ELECTRO

CHEM

ISTRY

Zn s + CuQk aq ⟶ ZnQk aq + Cu(s)

103


CHEM

ISTRY


OXIDATION REDUCTION

AN OIL RIG CAT

loss of electrons gain of electronsoccurs at the anode occurs at the cathode

104

ELECTRO

CHEM

ISTRYELECTROCHEMICAL SERIES

Page 4 in your data book! 106

• So we’ve seen that the following reaction will able to be used in a galvanic cell to generate electrical energy:

• What if we replaced CuQkwith MgQk, would we still be able to generate electrical energy?

ELECTROCHEMICAL SERIES ELECTRO

CHEM

ISTRY


Zn s + MgQk aq ⟶ ZnQk aq + Mg(s) ??????Answer: No!

Key point: The EC series allows us to predict whether a reaction will occur spontaneously or not.

107

ELECTRO

CHEM

ISTRYELECTROCHEMICAL SERIES


Zn s + MgQk aq ⟶ ZnQk aq + Mg(s)

✔ spontaneous

✖ not spontaneous

If the oxidant (left hand side) is above the reductant (right hand side), the reaction will spontaneously occur!

108

• What if there are multiple reactions possible?Preferential oxidation/reduction!

Example: If we add Cu(s) and Pb(s) to a Agk solution…

ELECTROCHEMICAL SERIES ELECTRO

CHEM

ISTRY

Key point: Strongest oxidant ALWAYSreacts with the strongest reductant!!!

109

ELECTROCHEMICAL SERIES

A series built upon thousands of rigorous scientific experiments

One changey boi

25.5 °C 1.2 M

1 atm

ELECTRO

CHEM

ISTRY

Key point: The EC series can only be reliably referenced under SLC conditions of 25 ℃ and 100 kPa.

110

• Fuel cells are a specific type of galvanic cell

• They still have half cells, electrodes, an external circuit, and convert chemical energy into electrical energy.

• However, unlike traditional galvanic cells, they do not ‘run out’ of charge and need recharging.

FUEL CELLS ELECTRO

CHEM

ISTRY


Key point: This is because, unlike primary or secondary cells, fuel cells do not store their reactants. Instead, the are continuously supplied from an external source.

112

HYDROGEN FUEL CELLS ELECTRO

CHEM

ISTRY

113

Image credit: Stanford University

H2O

H" g ⟶ 2H- aq + 2e# O" g + 4H-(aq) + 4e# ⟶ 2H"O(g)

OXIDATION REDUCTION

HYDROGEN FUEL CELLS ELECTRO

CHEM

ISTRY

Image credit: geek.com

Key point: Fuel cells don’t store reactants or products, they continuously get supplied & exhaust them.

114

• As we can see, the fuel cell is pretty much the same as a galvanic cell, except that we’ve got continuous supply of reactants.

• This is the main difference between other galvanic cells and fuel cells. If on an exam you’re asked for a difference, this is the one you should go to first!

• However, there are a few other subtle differences, including:– Properties of the electrodes used– Operating temperatures– The role of the electrolyte – What they’re used for

• Many different fuels can be used in fuel cells. We’ve seen hydrogen, another common fuel is methanol.

FUEL CELLS ELECTRO

CHEM

ISTRY

115

ELECTROLYTIC CELLS

• Electrolytic cells are the reverse of galvanic cells.

• Non-spontaneous redox reactions are driven forwards by input of energy (electrical current)

• Electrodes are inserted directly into electrolyte and current passed through

ELECTRO

CHEM

ISTRYCHEMICAL ENERGY

ELECTRICAL ENERGY

116

Cathode reaction Reduction Reduction

Anode reaction Oxidation Oxidation

Direction of flow Anode to cathode Anode to cathode

Cathode polarity + -

Anode polarity - +

Negative electrode Where electrons are lost (anode) Where electrons are gained (cathode)

Salt bridge Cations to positive cathodeAnions to negative cathode

“Maintain electrical neutrality”

None

Separation of reactants Must be separated Don’t need to be separated

GALVANIC VS ELECTROLYTIC ELECTRO

CHEM

ISTRY

GALVANIC ELECTROLYTIC

117

Electrolyte will contain several redox-active species.• Strongest oxidant is reduced at the

cathode• Strongest reductant is oxidised at the

anode• Molten electrolytes: quite simple to

determine the oxidant/reductant.• Remember to consider H2O in the case of

an aqueous electrolyte!

ELECTROLYTIC CELLS ELECTRO

CHEM

ISTRY

118

• NaCl (l)– Species present? – Strongest oxidant?– Strongest reductant?

• NaCl (aq)– Species present?– Strongest oxidant?– Strongest reductant?– Water is “preferentially reduced and oxidized”

ELECTROLYTIC CELLS ELECTRO

CHEM

ISTRY

119

• There are two basic types of cells/batteries:

SECONDARY CELLS ELECTRO

CHEM

ISTRY

PRIMARY CELLS

SECONDARY CELLS

Non – rechargeable RechargeableDisposable Re-usable

Image credit: Wikipedia 120


CHEM

ISTRY


CHEMICAL ENERGY

ELECTRICAL ENERGY

Galvanic cell

Recharging

Discharging

Electrolytic cell

121

• Secondary cells are rechargeable – can be driven forwards (like galvanic cells) but also backwards (like electrolytic cells)

• Requirements for being a secondary cell:• Discharge reaction must be reversible• Products of discharge must remain in contact

with electrodes

• Polarity of electrodes will never change (+ or -)

• Anode and cathode will swap between recharge and discharge.


CHEM

ISTRY

122

SECONDARY CELLS - DISCHARGE ELECTRO

CHEM

ISTRY

123

SECONDARY CELLS - RECHARGE ELECTRO

CHEM

ISTRY

124

VCAA 2009

PRACTICE QUESTION ELECTRO

CHEM

ISTRY

TOPIC 4: ORGANIC

CHEMISTRY

126

ALKANES, ALKENES & ALKYNES

127

OR

GAN

IC

# of carbons in chain Prefix descriptor

1 meth–2 eth–3 prop–4 but–5 pent–6 hex–7 hept–8 oct–

Image credits: VCAA Chemistry 3&4 Design

CH3CH2CH2CH3 Butane

Pent-2-ene

Oct-1-yne

• Naming simple hydrocarbons is easy! But what are the general steps for naming any organic compound?

MUST know these off by heart!

NAMING ORGANIC MOLECULES

128

OR

GAN

IC

IUPAC naming conventionSteps:1. Identify the ‘class’/primary functional group in compound2. Identify longest carbon backbone containing primary functional group3. Pick end closest to the first substituent (if both ends equidistant, need to

prioritise)4. Number down longest chain, noting substituents and their positions5. Put the name together


129

OR

GAN

IC

1 - chloropropaneHaloalkaneHalo group

propan-1-olAlcoholHydroxyl group

propanoaneKetoneCarbonyl group

propanalAldehydeCarbonyl group

propanoic acidCarboxylic acidCarboxyl group

Methyl ethanoateEsterEster group

propanamineAmineAmino group

propanamideAmideAmide group

Alcohols: R—OHAlcohols can be classified as being primary (1°), secondary (2°) or tertiary (3°)• This affects the exhibited reactivity!

Primary (1°) Secondary (2°) Tertiary (3°)


130

OR

GAN

IC


131

OR

GAN

IC

• You need to know how to name compounds with up to two different functional groups.

• So how do we name something with two different functional groups?

• Two suffixes??? Well….. no :(

• Remember, different functional groups have different ‘priorities’!


132

OR

GAN

IC

Functional group Suffix /Prefix Alternative

Highest priority Carboxyl -oic acid ------

Hydroxyl -ol hydroxy-

Amino -amine amino-

Alkene -ene -en-

Alkyne -yne -yn-

Lowest priority Halo Halo- -------

NAMING ORGANIC MOLECULES - EXAMPLE

133

OR

GAN

IC

• Give the systematic name of the following molecule.

NAMING ORGANIC MOLECULES - EXAMPLE

134

OR

GAN

IC

• Give the systematic name of the following molecule.

2-hydroxybutanoic acid

NAMING ORGANIC MOLECULES – YOUR TURN

135

OR

GAN

IC

Give the systematic name of the following molecule.

• Today we’ll have a quick look over some of the reactions that you need to know.

1. Substitution reactions (involving alkanes and haloalkanes)

2. Addition reactions (involving alkenes)

3. Oxidation (of alcohols)

4. Esterification reactions (between alcohols and carboxylic acids)

5. Hydrolysis reactions (of esters)

ORGANIC REACTIONS

136

OR

GAN

IC

1

2

3

45

• Substitution reactions involve swapping out one atom/group of atoms in a molecule for another.

• Haloalkanes can be synthesised via a substitution reaction of an alkane with a halogen molecule.

FUNCTIONAL GROUPS & ORGANIC REACTIONS

Gif: Wikipedia commons

ORGANIC REACTIONS - SUBSTITUTION

137

OR

GAN

IC


+ UV light+


138

OR

GAN

IC

• UV or heat is required to break apart halogen molecule, acts as a catalyst.• MUST write UV light or heat above the arrow to get full marks!

Substitution of alkanes

Substitution reactions of alkanes• UV or heat is required to break apart halogen molecule, acts as a catalyst!

• MUST remember to include UV light or heat when writing out equation• In principle substitution may occur anywhere and produce a wide range of

potential products (incl. polyhalogenated products)

ORGANIC REACTIONS - SUBSTITUTION OR

GAN

IC CHEM

ISTRY

Substitution of haloalkanes• Haloalkanes can also under substitution reactions!• Haloalkanes are much more reactive than alkanes because of their polar bond,

and undergo a bunch of different types of substitution.• One such example is the formation of an alcohol by substituting in a hydroxyl

group, which can undergo further substitution to then form an amine.

NaOH (aq)

𝛿<𝛿.


140

OR

GAN

IC

+

+Al2O3, 400°C

Addition reactions of alkenes• Alkenes have a C=C double bond and are unsaturated• Extra substituents can be added across the double bond in an addition reaction.

• Compared to alkanes, alkenes are fairly reactive (due to double bond, which is not as stable as a single bond)

• Unlike substitution reactions, there is no inorganic product formed. • 3 main types of addition reactions….

+

ORGANIC REACTIONS - ADDITION

141

OR

GAN

IC

ORGANIC REACTIONS - ADDITION

142

OR

GAN

IC

Catalyst

1. Hydrogenation – Addition of H2

H2+2. Halogenation – Addition of X2 (e.g. Cl2)

+

3. Hydration – Addition of H2O

H2O+H3PO4

300 °C

Cl2

Oxidation reactions of alcohols• Primary and secondary alkanols can be oxidised by strong oxidants, e.g.

H+/Cr2O72- (nasty) or H+/MnO4

- (even nastier)• Acidification of the reagent is important!• Oxidation occurs naturally too (but slowly) in the presence of O2(g)Primary alkanols undergo 2-step oxidation

Primary alkanol → aldehyde→ carboxylic acidSecondary alkanols undergo 1-step oxidation

Secondary alkanol → ketoneTertiary alkanols don’t undergo oxidation L

FUNCTIONAL GROUPS & ORGANIC REACTIONSORGANIC REACTIONS - OXIDATION

143

OR

GAN

IC

Oxidation of primary alkanols

Oxidation of secondary alkanols

H+/MnO4-

H+/MnO4-

H+/MnO4-

ORGANIC REACTIONS - OXIDATION

144

OR

GAN

IC

Esterification reactions• Reaction of a carboxylic acid with a primary alcohol yields an ester• This is a condensation reaction that releases H2O• Need to heat reaction mixture in the presence of concentrated H2SO4

• Concentrated is important – in general avoid writing H2SO4(aq)• Conc. H2SO4 or H2SO4(l) are acceptable


+ +

ORGANIC REACTIONS - ESTERIFICATION

145

OR

GAN

IC

H2SO4(l)

REACTION PATHWAYS

146

OR

GAN

IC

• Knowing individual reactions is all well and good, but the really important part is being able to use these reactions to convert one compound into another!

• The sequence of reactions required to transform some starting reactant to a desired final product is called a reaction pathway.

• VCAA almost always ask about reaction pathways, so need to know all reactions really well!

REACTION PATHWAYS

147

OR

GAN

IC

Cl2(g)

UV light NaOH(aq)

H+/Cr2O7-

H2SO4(l)

PRACTICE QUESTION

148

OR

GAN

IC

VCAA 2013 Question 6

JOSHVCE

150

PROMO

BLOCK 2: QUESTION TIME

BREAK SLIDE

TOPIC 5: ANALYTICAL CHEM

NMR

IRMS

HPLC

me and the boys solving analysis questions

WHAT TECHNIQUES DO YOU NEED TO KNOW?

154

SEPERATE IDENTIFY QUANTIFY

CHROMATOGRAPHY SPECTROSCOPY VOLUMETRIC ANALYSIS

PAPER HPLC MS IR NMR ACID - BASE REDOX

ANALYTICAL

• So we can use chromatography to separate out mixtures into pure compounds, but how do we actually find out what these pure compounds are?

• Well, we can use spectroscopic techniques!• Spectroscopic techniques generally rely on the interactions between

electromagnetic radiation and a compound/solution of interest.

• If we have an unknown organic molecule, what might be useful to know in order to identify it? • Molecular mass• Functional groups• Connectedness

SPECTROSCOPY

155

IDENTIFY

MASS SPEC.IR SPEC.

NMR SPEC.

ANALYTICAL

MASS SPECTROMETRY

Ethanoic acid +

+

+

+

m/z = 15

m/z = 43

m/z = 45

m/z = 60

ANALYTICAL

156

• Largest peak (base peak) is assigned relative intensity 100%

• Highest molecular weight peak corresponds to parent molecular ion

• Tiny peaks (usually ±1) about the molecular ion peak due to isotopes, e.g. 13C, 35Cl/37Cl, 79Br, 81Br

MASS SPECTROMETRYAN

ALYTICAL

157

Key features of an infrared spectrum• Region below 1500cm-1 is the

fingerprint region• Absorption in this region is

characteristic of the molecule as a whole (not due to individual bonds)

• Peaks above 1500cm-1 indicate the presence of particular bonds, e.g. C—H, O—H, C=O, etc.

• Pay attention to intensity, sharpness and shape of bands.

INFRARED SPECTROSCOPY

158

ANALYTICAL

• Two types of nuclear magnetic resonance spectroscopy:– Proton/1H NMR– 13C NMR

• Can be used to figure out how our molecules are ‘connected’!

• Key things to know:• Environments • 𝑛 + 1 rule to determine peak splitting• Chemical shifts• Area under peaks

NMR SPECTROSCOPYAN

ALYTICAL

159

Proton NMR1H NMR spectra look like this…• Shows peaks at different ‘chemical shifts’

(𝛿, in ppm)• Each peak corresponds to a unique

proton environment• Note that peaks take different areas and

also are split into ‘subpeaks’• The position, area, and splitting of these

peaks contains information about the structure of the compound

Source: http://sdbs.db.aist.go.jp/sdbs

NMR SPECTROSCOPYAN

ALYTICAL

160

NMR SPECTROSCOPYEnvironments

• Atoms in the same environment appear as the same peak or split peaks in NMR.

• Hydrogen atoms in the same environment are said to be equivalent. • If the molecule is not symmetrical, each carbon is an environment

Number of environments = Number of peaks on spectrum

ANALYTICAL

161

This leads us to the 𝑛 + 1 rule:• Number of peaks for a particular hydrogen environment is 𝑛 + 1, where 𝑛 is the

number of hydrogens in a different hydrogen environment on adjacent carbons (neighbouring hydrogen environments)

We have names for split peaks…

NMR SPECTROSCOPYAN

ALYTICAL

162Source: Wikipedia

• Individual spectroscopic techniques can only provide limited information• However, each comprises only part of the toolset available to an analytical

chemist• Combination of MS, IR, 1H and 13C NMR techniques is key to elucidation of

chemical structures.

SPECTROSCOPIC PROBLEM SOLVING

Technique Information providedMass spectroscopy Molecular weight, parts of structure

(limited)Infrared spectroscopy Functional groups presentNMR (proton and 13C) Connectivity of atoms in compound

ANALYTICAL

163

• You could be presented with a variety of spectra/details:– Mass spectrum– IR spectrum– Carbon NMR– Proton NMR– Additional chemical information (e.g. empirical formula)– Qualitative information (e.g. it has a sweet odour)

• Because every molecule is different, every question will be different, but I’m gonna show you a general framework you can use for tackling these kinds of questions!

TACKLING ANALYSIS QUESTIONSAN

ALYTICAL

164

1. Identify non-spectral information

Is there a molecular formula given?Is there a partial formula given? (e.g. CxHyO2 might suggest a carboxylic acid or an ester)What do we know about the molecule? (e.g. mixes with water suggests a polar compound)

This information can tell you what to expect before you even look at the spectra à very valuable!


ALYTICAL

165

2. IR spectrumNext, I recommend you look at the IR spectrum. Why?• Functional groups! This is one of the easiest things to identify, but

also one of the most important pieces of information.

3. Mass spectrum• Pretty much just for molar mass• Useful if you were given empirical formula, otherwise not really

By this stage, you could probably say something like:“I know I have an alcohol with molar mass 46”


ALYTICAL

166

4. NMR

H vs C NMR:• H NMR tells you more about the molecule – most useful• I just use C NMR for number of C environments and to

confirm predictionsI like to look at NMR last. Why?• Knowing the functional groups already can help you pick

the right identity for each peak if there is any ambiguity• Hardest, so the more you know by the time you get to

NMR, the better


ALYTICAL

167

• Let’s see how this applies to a specific question (adapted from VCAA 2013)

• A sample of species X was analysed using mass spec, IR spectroscopy and NMR and spectra were produced. The sample was then heated in the presence of H+/MnO4

- for an extended period of time. It was analysed again. It was found that the new spectra produced were the same as the original spectra. They are shown below. Identify species X.

• What do we know about species X already?

EXAMPLE

Answer:We know that it stayed the same after heating in those conditions → it was not oxidised. This tells us that species X is NOT a primary/secondary alcohol or an aldehyde.

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• Molar mass:

• Possible functional groups?

EXAMPLE

88 g mol-1

Carbonyl C=O

→ Ester or ketone

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EXAMPLE

• What can we predict from these spectra?

4 carbon environments, so at least 4 C atoms

Quartet and triplet, -CH2CH3

Singlet at 2.0 suggests CH3COO – R.

ANALYTICAL

• Bring information together to determine identity:

EXAMPLE

Ethyl ethanoate

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• There is no one right way to do spec questions• Do what makes the most sense for you

• Just remember:– Don’t ignore any information– Usually these questions have many parts, and you might need info from part (a) and (b) to do

part (d), for example– The ranges of chemical shifts for H NMR often overlap, so be careful when assuming what

caused each peak

KEY POINTSAN

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• https://create.kahoot.it/share/atarnotes-chem-3-4-spring-lecture/e5eabb93-a077-411e-b0d5-aa88be94427b

KAHOOOOOOOOOT

https://create.kahoot.it/share/atarnotes-chem-3-4-spring-lecture/e5eabb93-a077-411e-b0d5-aa88be94427b

COUNTDOWN

Days until the Chem exam:

43 days!

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EXAM ADVICE

How is VCE Chemistry assessed?

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UNIT 3 UNIT 4 EXAM

16% 24% 60%Exam is easily the most important assessment!

Don’t stress, you’ve done most of the hard work already!

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EXAM ADVICE

What’s the deal with the exam?

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30 multiple choice marks90 short answer marks 120 marks total, 150 minutesIt’s hard :(

You can have a look through them on VCAA’s website.Exams available all the way back to 2002. Not all questions will still be relevant, but many still are!

Scientific calculator & data booklet permitted

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BLOCK 3: QUESTION TIME

GOOD LUCK! <3

TOPIC 5: EXAM TIPS

VCAA wants a single exam to determine 60% of your study score

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• Exam advice can be broken down into two sub areas:

EXAM ADVICE

EXAM ADVICE

EXAM PREPARATION EXAM STRATEGIES

à What to do before the exam à What to do during the exam

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EXAM PREPARATION

8 QUICK TIPS

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• This stuff worked for me, but everyone is different!

• Have a think about some of these suggestions, and think if they’d suit you and how you think you learn best.

• Ultimately, even though we don’t really like to admit it, VCE (in terms of results anyway) is literally a competition. Treat it like you would any other competition, train hard and prepare well!

DISCLAIMER EXAM

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1. Forget about your SACs... kind of?

• SACs are (hopefully, R.I.P. if not) over, and you can’t change your marks now.

• The good news? SAC marks probably don’t matter as much as you think.

• Most important thing is to learn from your SACs. Go back over them if you can, identify the errors you made and make sure you don’t make those same mistakes again.

EXAM PREPARATIONEXAM

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2. Make sure you understand all the content!

Don’t do heaps of questions just for the sake of it!• Questions are important, but concepts are even more important.

• Trying to get as much ‘exposure’ is only going to get you so far – but understanding the concepts behind topics will allow you to figure questions out on the fly!

• Write a list of questions on things you’re not sure about, and then make sure you find someone to help you with them.

• Ask friends, teachers, tutors, the internet, but whatever you do make sure you really understand all the theory.


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2. Make sure you understand all the content!But I don’t even know what I don’t know :’’’’(

Directed study• Focus on points of weakness!• Refer to the study design for assessable topics – tick off all the points!

Textbooks and notes• Can provide a different perspective on topics, and double check that you haven’t

missed anything!• Don’t be afraid to go back to the textbook! It’s normal to forget bits and pieces,

but make sure you identify points of weakness and brush up!


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2. Make sure you understand all the content!Remember…

It’s a little bit how much you study, but more how you study!

Sure, we need to work hard. But we need to work efficiently too =)

Think to yourself… • Which topics am I struggling the most with right now?• Why don’t I understand these topics?• What resources do I have that would help me understand this better?• Understanding more means remembering less.


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3. Get cosy with your data booklet!

• At this stage you should pretty much be bffs with the data booklet, you’ll need to use it A LOT

• Don’t have time in the exam to spend half a minute looking for something every time.

• Make sure you know what’s in it, what’s not, and where to find it.


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4. Don’t neglect revising and practising experimental design!• Number of marks on the end of year exam for scientific knowledge and

experimental design in…


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0

2

4

6

8

10

12

14

16

18

Number of marks for experimental design on VCAA exam

2013 2016 2018

4. Don’t neglect revising and practising experimental design!


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• So there is an increased focus by VCAA in wanting you to be able to think about experimental design and errors.

• Yet, these questions keep being answered poorly. See these two experimental design questions from the 2018 exam:

• How to get good at these? Practice practice practice!

5. Practice (exams) makes perfect!

• VCAA is the golden standard, the best exams by far (apart from ATAR Notes exams of course hahaha)

• How many? Everyone is different! Quality of practice exams much more important than quantity.

EXAM PREPARATION

# of prac. exams

‘value’

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6. Make your practice exams count!

• How you approach each practice exam is WAY more important than how many you do though.

• You could do 100 practice exams, but if you didn’t mark them, it would be a waste of time…

• So how to make practice exams ‘count’?


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USE READING TIME IN PRACTICE EXAMS!

• In my experience, not enough people give reading time the respect it deserves ;-;

• You’re given fifteen minutes to read for a reason. When you’re completing practice exams, you can PRACTICE using reading time, and figure out how to use it most effectively by the time the actual exam roles around.


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REPLICATE EXAM CONDITIONS AS CLOSELY AS POSSIBLE

• Try to do a few practice exams in the same room as your actual exam

• Do them at a similar time of day to the actual exam, so your body can get in the groove

• Take away your phone and any distractions, sit down and do them in silence, in one, uninterrupted period.


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CHOOSE CAREFULLY WHEN YOU DO THEM

• Make sure you’re not too stressed, tired, hungry etc.

• Make sure you don’t leave them too late, don’t want to be doing them the night before the actual exam! Personally, I didn’t do any the entire week before the exam.

• Print out a calendar, and plan on what days you’re gonna do practice exams for each subject, so you can get a feel for how much time you have.


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CHOOSE CAREFULLY WHAT PRACTICE EXAMS YOU DO

recent VCAA exams


ADVICE

2015, 2016, 2017 NHT, 2018 NHT, Sample exam, 2017, 2018

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KEEP TRACK OF YOUR MISTAKES


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7. The day before…• Maybe your last exam??? THE END IS IN SIGHT!!!

• Just chill, you’ve already put in all the hard work. Learning stuff is the difficult part, kick back and get ready for the “easier” part!

• Lightly brush over past mistakes, and consider making an exam plan!


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7. The day before…

• Lightly brush over past mistakes, and consider making an exam plan!


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8. Most importantly…

• Look after yourselves <3

• Don’t stress too much, get plenty of sleep, eat well, exercise if you can.

• Cliché stuff but being healthy for the exam is as important as having studied for it!


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EXAM STRATEGIES: IN THE EXAM

4 QUICK TIPS

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1. Don’t panic!! (easier said than done)• Once you begin to panic in the exam, it can really easily spiral out of

control, and make even easy questions seem impossible.

• If you think this might be a problem for you, use practice exams as an opportunity to help develop some strategies to manage the panic levels.

• For example, I managed this by not completing the exam in order, but doing all the questions that I was confident about first, get them out of the way, and go into the more tricky questions on a bit of a roll and feeling good!

EXAM STRATEGIES: IN THE EXAMEXAM

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2. Manage your writing time• Are you going to answer the questions in the order they appear? Or will

you answer the easier questions first and hit the ground running? Figure out what works best for you!

• First 30s of writing time – jot down a few milestones to keep on track. For example, might be something like:• Should finish with multiple choice by 9:45 am• Should be halfway through extended response by 10:45 am

• Make sure you check the clock pretty regularly (every 10-20 minutes)! No worse shock than hearing you’ve got 10 minutes left when you though you had plenty of time.


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3. Multiple choice question answering • I think we’ve all heard the usual ‘eliminate options you know are wrong’ etc.

etc, but one thing I don’t think gets talked enough here is making sure you actually write some working out for mathsy multiple choice questions!


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4. Avoid silly mistakes!• I think everyone suffers from this to an extent– it’s

always a problem, but you can minimise it!• Use a highlighter and pay special attention to key

and bolded words.• If VCAA says ‘you may use’ something (e.g. a

diagram) in your answer, you definitely should!• Use reading time effectively.• Have a mental checklist of things that can go

wrong.


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4. Avoid silly mistakes!• I personally found it really difficult to pick up on my own mistakes when

checking over my exam at the end.• Instead of rushing through and checking over at the end, I found it much

more effective to go a bit slower and get as much possible right the first time. • To do this, I used the read, read, answer and reread method.• This involves:

• Reading the question once quickly to get an idea of what its about and what it’s asking.• Reading it again a second time in more detail, looking for any tricks, thinking about what

the marks will be allocated for. • Writing the answer.• Rereading the question right after you answer it, to check you actually answered the

question, gave the right units etc.


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• Any questions, come ask! I’ll be around afterwards

• Don’t stress (too much), don’t burn yourself out!

• Study smart, and look after yourself pls

• And finally…

THAT’S IT!

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Documents

VCE CHEMISTRY 3&4 REVISION LECTURE SPRING 2021