C11 Organic Chemistry: Alkanes and Combustion

C11 Organic Chemistry Part 1 Overview

• Students will learn about alkanes' structures, extraction, reactions, and measurements of energy transfers
• Other organic compounds will be discussed later in the term

NESA Stage 5 Syllabus: Organic Chemistry

• Can distinguish between organic and inorganic compounds
• Can employ IUPAC nomenclature to name organic compounds
• Can identify and reproduce the structure of C1-C8 alkanes
• Can describe the differences between complete and incomplete combustion reactions of hydrocarbons, citing everyday applications to compare the products and energy released
• Can explain how hydrocarbons are separated from crude oil, identifying their specific uses
• Research: Can research and describe how the use of hydrocarbon compounds has changed over time

Lesson Sequence

• Alkanes
• Complete and incomplete combustion
• Balancing equations
• Calorimetry calculations & experiments
• Fractional distillation

Alkanes

• The learning intention is to distinguish between organic and inorganic compounds
• Also, learning to name and model the alkanes

Key Words

• Organic compound: A covalent compound that contains carbon.
• Hydrocarbon: A compound made of only carbon and hydrogen
• Alkane: A hydrocarbon with only single bonds
• Methane (natural gas) is used for cooking and heating
• Propane is used in gas cylinders for homes
• Butane is sold in blue cylinders for camping gas
• Octane is a component of petrol

True or False Questions

• Every alkane is a hydrocarbon and an organic compound
• Alkanes have double bonds
• Organic compounds are grown without pesticides
• Hydrocarbons can contain oxygen
• C4H10 is a hydrocarbon
• CaCO3 is an organic compound

Alkane Formulas

• Alkanes have the general formula CnH2n+2
• Carbons are arranged in a chain, with hydrogens bonded around them
• Alkane Names, n, 2n+2, and Formula:
• Methane: 1, 4, CH4
• Ethane: 2, 6, C2H6
• Propane: 3,
• Butane: 4
• Pentane: 5
• Hexane: 6
• Heptane: 7
• Octane: 8

Naming Alkanes Methodology

• Use molymods to build an alkane structure with up to 8 carbons
• Have someone count the carbons and name the alkane using the table
• Work out the alkane's formula, don't count the hydrogens

Alkane Formulas

• There are three ways to show an alkane formula:
• Molecular formula eg. C3H8
• Structural formula
• Skeletal formula
• In a skeletal formula, the end of each straight line is a carbon atom, and hydrogens are not shown.

Formulas of other Alkanes

• Molecular formula, Structural formula, and Skeletal formula can be used to describe the following compounds:
• Pentane
• Ethane
• Hexane
• Butane
• Octane
• Heptane
• Methane

Success Criteria

• Can identify organic compounds with covalent bonds and contain carbon
• Can identify molecular, expanded structural and skeletal structural formulas
• Can name, draw, and model alkanes with 1–8 carbon atoms

Complete and Incomplete Combustion

• Learning Intention: Describe the differences between complete and incomplete combustion reactions of hydrocarbons

Key Words: Combustion

• Combustion: An exothermic reaction between a fuel and oxygen
• Complete combustion: A reaction that uses the most amount of oxygen, producing carbon dioxide and water
• Incomplete combustion: A reaction that uses less oxygen, producing carbon, carbon monoxide, and water, and transfers less energy
• Carbon soot: A black powder with formula C(s)
• Carbon monoxide: A toxic gas with formula CO(g)

True or False

• Combustion reactions emits heat
• Complete combustion uses more carbon than incomplete combustion
• Complete combustion transfers more energy than incomplete combustion
• Carbon monoxide is a black solid

Combustion Products

• When lots of oxygen is available, combustion produces carbon dioxide
• When less oxygen is available, combustion produces carbon monoxide or even solid carbon
• Carbon monoxide is an invisible toxic gas and homes have carbon monoxide alarms
• Solid carbon is 'soot' and is a black powder.

Fill in the Gaps

• In a complete combustion reaction, the products are oxygen and carbon dioxide, because there is sufficient oxygen for the carbon. Most thermal energy is transferred.
• In incomplete combustion, not enough oxygen is used react. The fuel’s carbon then either becomes carbon monoxide, a toxic gas, or more simply solid carbon, which is a black powder.

Bunsen Burner

• Adjusting the collar on a Bunsen burner changes the amount of air containing oxygen that can mix with the methane gas fuel.
• With a lot of oxygen, a blue flame is produced. With less oxygen, a yellow flame is produced.

Testing Complete and Incomplete Combustion

• Set up a Bunsen burner, tripod, gauze mat, bench mat, and 50ml of cold water
• Heat the water with a blue flame and record the time it takes to boil
• Repeat with a new beaker and water, using a yellow flame
• Observe the two beakers

Observations Questions

• Which beaker heated quicker, from the blue or yellow flame?
• Which beaker is covered in solid carbon, from the blue or yellow flame?
• Which flame do you think is complete combustion?

Discussion Questions

• The blue flame is hotter because there is plenty of oxygen available for combustion which transfers the most heat.
• Soot is found from the yellow flame because incomplete combustion occurs

Success Criteria: Combustion Equations

• Can identify the reactants and products of a complete combustion reaction
• Can identify reactants and products of an incomplete combustion reaction
• Can outline the dangers of incomplete combustion

Balancing Chemical Equations

• Balances the elements within reactants and products during combustion reactions

Keywords

• Balanced chemical equation: An equation with the same number of each atom in the reactants and products
• Subscript: A small number in a chemical formula that multiplies one type of atom or ion. A subscript can't be changed; an example is CO₂
• Stoichiometric coefficient: A large number placed before a formula that multiplies the whole chemical formula, and can be changed to balance an equation

Atom Quantity Question

• Given a chemical formual, what elements does it contain & how many of each? e.g.:
• C6H12O6, has Carbons x6, Hydrogens x12 and Oxygens x6
• HNO3
• NH4Cl
• K2SO4
• AgBr

Atom Quantity With Coefficient Question

• Given a formula containing a coefficient, what elements does it contain & how many of each? e.g.:
• 2C6H12O6; Carbons x12, Hydrogens x24, and Oxygens x12
• 6HNO3
• 3NH4Cl
• 7K2SO4
• 4AgBr

Atoms in Reactions and Products

• To have a balanced stochiometric reaction, for each element the number of atoms must be the same in both the reactants and products
• C3H8 + 502 -> 3CO2 + 4H2O has Cx3, Hx8, Ox10 on both sides
• HCl + NaOH → NaCl + H₂O
• H2SO4 + CaCO3 → CaSO4 + CO2 + H₂O
• 2HCl + Ca(OH)2 → CaCl2 + 2H₂O

Balancing Assessment

• Questions about whether a reaction is balanced e.g.:-
• C4H10 + 502 → 3CO₂ + 5H2O
• C2H6 + 3.50₂ → 2CO2 + 3H2O
• C7H16 + 70₂ → 7CO₂ + 16H₂O

Strategies for Balancing Combustion Equations

• Take the subscript for carbon in the fuel, and use it as the coefficient for carbon dioxide
• Then take the subscript for hydrogen in the fuel, divide it by 2, and use that as the coefficient for water
• Finally, add up all the oxygens in the products, divide it by 2, and use it as the coefficient for oxygen.
• Example: C3H8 + O2 → CO2 + H2O
• Carbon subscript = 3, so the CO2 coefficient is 3: C3H8 + O2 → 3CO2 + H2O
• Hydrogen subscript = 8, divided by 2 is 4, so the water coefficient is 4: C3H8 + O2 → 3CO₂ + 4H2O
• Total oxygen in the products is 10, divided by 2 is 5, so: C3H8 + 502 → 3CO2 + 4H2O

Balancing Examples

• CH4 + O2 → CO2 + H2O
• C5H12 + O2 → CO2 + H2O
• C4H10 + O2 → CO2 + H2O; be sure to include a decimal
• C2H6 + O2 → CO + H₂O
• C6H14 + O2 → C + H₂O
• Write and balance: complete combustion of octane
• Write and balance: incomplete combustion of methane, forming carbon monoxide
• Write and balance: incomplete combustion of pentane, forming carbon

Completion Criteria

• A balanced equation has same the number of atoms in reactants and products
• Adjust a substance’s stochiometric coefficient to strike an equation balance
• Can balance both complete and incomplete combustion equations

Calorimetry calculations

• Learning Intention: Apply calorimetry techniques to measure the amount of energy released from fuel combustion

Keywords: Calorimetry

• Calorimetry: measurement of change in thermal energy where Calorie = energy, and metry = measurement
• Specific heat capacity: The amount of energy required to heat 1g of an object by 1°C
• Heat of combustion: The amount of energy released in combustion of 1g of a fuel

Calorimetry

• Calorimetry measures changes in thermal energy
• In it, energy released from an exothermic reaction is absorbed by water
• The amount of energy released by the chemical reaction is found by measuring the temperature change

Absorbing Thermal Energy

• When a substance absorbs thermal energy, its temperature increases.
• The temperatures of some substances such as solid iron increase fast, while temperatures of others like liquid water increase slowly.
• Water's specific heat capacity is 4.18 Joules per gram, per degree Celsius

Calorimetry: True or False

• Absorbing thermal energy reduces an object's temperature
• It takes the same amount of energy to increase an object’s temperature by 1°C
• Liquid water takes more energy to increase temperature than solid iron does
• All objects have a specific heat capacity of 4.18 J/g/°C

Calculating Heat Absorption by Water

• The amount of heat absorbed by water can be calculated by the formula q = m c AT
• q = heat absorbed (J)
• m = mass of water
• C = specific heat capacity of water = 4.18J/g/°C
• ∆T = change in temperature (°C)
• Example: What heat's absorbed when 100ml of water is heated from 20°C to 27°C?
• m = 100g; ∆T = 7°C
• q = 100 x 4.18 x 7 = 2926J
• q = 2.926kJ

Calculation Exercises

• Calculate the heat absorbed by 100ml water given the following temperature changes:
• Initial (18°C), Final (48°C)
• Initial (25°C), Final (100°C)
• Initial (21°C), Final (33°C)
• Initial (15°C), Final (62°C)

Heat of Combustion Calculation

• The heat of combustion (ΔΗ) of a fuel indicates how much heat's transferred when 1g's combusted. Methane's heat of combustion is 55,500 Joules/gram.
• Heat of combustion = heat absorbed (J) / mass of fuel combusted (g)
• Formular: ∆H = q / m
• To calculate, say you start with 25.50g of fuel, finish with 24.75g, and transfer 45,000J of energy. You would do (ΔH) = 45,000 / 0.75; then ΔΗ = 60,000J/g

Combustion Calculations

• Practise heat of combustion, give the following:
• The Heat transfer
• Initial mass of fuel
• Final mass of Fuel
• Mass of fuel used
• The heat of combustion

Example

• You burn a fuel to heat 100 mL of water from 20°C to 35°C. The fuel’s initial mass was 95.50g, the final mass was 95.20g. You then do this:
• m(water) =100g
• ΔΤ = 35 – 20 = 15°C
• q = m c ΔT
• q = 100 x 4.18 x 15
• q = 6270J
• Then to calculate heat of combustion, you would do:
• m(fuel) = 95.50-95.20 = 0.20g
• ΔH = q / m
• ΔH = 6270 / 0.20
• ΔH = 31350J/g
• Now try to answer this: you burn a fuel to heat 100 mL of water from 18°C to 28°C. The fuel’s initial mass was 120.95g, the final mass was 120.55g.
• Answer this: You burn a fuel to heat 100 mL of water from 24°C to 58°C. The fuel’s initial mass was 208.34g, and the final mass was 207.56g.
• One last one: You burn a fuel, heating 100ml water from 22°C to 88°C. The initial mass of the fuel was 96.28g, and the final mass was 95.13g

Success Criteria: Calorimetry

• Be able to identify that a combustion reaction transfers chemical potential energy to thermal energy
• Recognize that thermal energy is transferred to water during calorimetry
• Successfully calculate energy using the formula q = 418 ΔT for 100ml of water
• Can then find heat of combustion with the formula ∆H = q/m

Calorimetry Practical

• The goal is to carry out a calorimetry experiment that is both safe, valid and reliable

Keywords: Calorimetry Experiment

• Calorimeter: A can of water heated with a fuel
• Reliable: An experiment that produces very similar results when you repeat it
• Valid: An experiment that's properly designed and undertaken, using controled variables
• Accuracy: A measurement that is close to the true value

Calorimetry Experimental Procedure

1. Prepare the retort stand and calorimeter
2. Measure 100ml water into the calorimeter, add a lid and thermometer, and note initial temperature
3. Record the starting mass of the spirit burner and its lid
4. Light the spirit burner under the calorimeter, and heat the water by approximately 20°C
5. Put out the spirit burner using the lid, then record the highest temperature reached by the water
6. Record the final mass of the spirit burner and lid

Validity of Calorimetry

• For calorimetry to be valid, all fuel energy must be transferred to the calorimeter water instead of escaping
• Ways to ensure this incluide:
• Add a lid to the calorimeter
• Construct the calorimeter out of copper instead of glass to better conduct heat
• Shield the flame, and avoid the usage of any gauze around the flame
• Ensure that there’s sufficient oxygen in the reaction, as incomplete combustion transfers less energy

Calorimetry Setup

• A good setup needs five elements:
• Thermometer
• Draught Shield
• Insulating card
• Clamped copper calorimeter
• Burner

Setup Improvement

• To make these setups more accurate, you can add these:
• Thermometer and lid
• Copper can
• Spirit Burner

Accuracy of Calorimetry

• The true value of heat combustion of methane is 55,500 J/g.
• If a student measures the amount of heat combustion and the result is 34,000J/g, then the result is inaccurate
• Poor results are often the result of utilizing invalid procedures; thus it is hard to carry out calorimetry accurately

Accuracy Question

• Knowing that the "True combustion value" of octane is 48,000 J/g, which of these measurements is the most accurate:
• Mick: 31,000 J/g
• Dave: 28,000 J/g
• Sarah: 42,000 J/g
• Sharon: 35,000 J/g

Reminder: Calorimetry Experiment

1. Prepare retort and calorimeter
2. Measure out 100ml water into the calorimeter, add lid + thermometer, then note the initial water temperature
3. Record the starting of mass the burner and lid
4. Light spirt burner under calorimeter to heat water ~20°C
5. Extinguish burner
6. Record final mass of the burner and lid

Procedure Comprehension Questions

• What 4 measurements are recorded?
• What holds the calorimeter?
• What holds the thermometer in place?
• How do you know when to extinguish flame?

Calorimetry Practical: Safety Notes

• The experiment has certain hazards such as open flames, hot water and equipment
• Tuck away any ties and hair, wear the appropriate safety goggles, and be careful when handling hot equipment
• The experiment requires you to:
• Follow the calorimetry procedure
• Set up equipment properly for a stable measuring
• Record any measurements using notes
• Repeat all your measurements for each fuel

Table: Calorimetry Trial 1,2,3

• You want to note:
• Mass of water
• The initial water temperature
• The final water temperature
• The water temperature change
• The transferred energy
• Initial fuel mass
• Final fuel mass
• Change in fuel mass
• Heat of combustion

Evaluate

• After conducting the experiment, evaluate the accuracy and consistency of all your measurements

Learning outcomes: Calorimetry Practice

• The experiment measures heat of burning of a fuel by safely following a procedure
• Reliable and repeatable results are attained by repeating the experiment
• Reliability is verified by experiment repetition and evaluated through measurement comparison
• Validity is verified and its experiment is evaluated
• Measurements and experiment are evaluated for accuracy
• Experiment is improved through thoughtful suggestions

Fractional Distillation and Uses of Hydrocarbons

• Goal is to desxribe how hydrocarbons can be separated from crude oil & identify the uses to which these products are then put

Relevant Keywords

• Distillation: A technique extracting liquids through boiling
• Fractional distillation: A method to refine crude oil that involves condensing fractions in certain locations
• Fraction: A family of hydrocarbons with a single boiling point
• Bitumen: A gloopy black mixture of large hydrocarbons.
• Petrol: A crude-oil based fraction that’s mostly octane

Distillation

• A mixture of liquids with boiling points is boiled
• Each boils separately at their own boiling points
• Each is separately condensed

Distillation, True or False?

• All liquids in mixture boil at the same temperature
• Two phases involved in distillation
• It can isolate 2 solids

Fractional Distillation

• A procedure involving a heated, fractionated oil (a hydrocarbon mixture) that is injected into a tower's fractionating column bottom
• Most hydrocarbons boil then rise, while some remain as liquids
• As such, at their boiling point, these gases turn cool, and group into hydrocarbons with uniform boiling points we call fractions

Gaps

• Crude oil and heated are added to extraction column
• Those point do not are bottom
• Smallest B
• The a and different columns

Distillation Assessment

• There 2 stages fractional
• Distillation Lots at one
• Fractions diff Parts
• Fraction Substance
• Top Column
• Low Low