Topic 14 - Hydrocarbons Flashcards
What are hydrocarbons made of?
Hydrogen and Carbon only.
What are alkanes?
Saturated hydrocarbons.
What does saturated mean?
No double bonds. Each Carbon atom is bonded 4 times with the max no. of Hydrogens possible.
What is the general formula for alkanes?
C(n) H(2n + 2)
What is the general formula for cycloalkanes?
C(n) H(2n)
What are cycloalkanes?
A functional group isomer of alkanes.
Where are alkanes found?
Crude oil.
What is crude oil?
A mixture of different length hydrocarbons.
How are alkanes in crude oil separated?
Fractional distillation.
Where do alkanes with the highest boiling point condense in fractional distillation?
At the bottom of the column.
Where do the shortest hydrocarbons condense?
At the top. Some may not even condense and be taken off the top as a gas.
Why do alkanes condense at different temperatures?
Different lengths and different boiling points.
How can gas from fractional distillation be used?
LPG and stove gas.
How can petrol from fractional distillation be used?
Petrol cars.
How can diesel from fractional distillation be used?
Diesel cars.
How can fuel oil from fractional distillation be used?
Ships and power stations.
How can kerosine from fractional distillation be used?
Jet fuel and heating.
How can bitumen from fractional distillation be used?
Roofing and tarmac.
Which fractions are more valuable and useful?
Lighter fractions.
How can more lighter fractions be made?
Cracking.
Heavier fractions can be cracked to higher demand lighter fractions.
What is cracking?
Breaking a longer chain alkane into shorter hydrocarbons.
What are the two types of cracking?
Thermal and catalytic.
What are the conditions for thermal cracking?
1000* C
70 atm
What are the products of thermal cracking?
Mainly alkenes.
What are alkenes used for?
To make polymers such as plastics.
What are the conditions for catalytic cracking?
450* C
Slight pressure
Zeolite catalyst
What are the products of catalytic cracking?
Mainly aromatic hydrocarbons used for fuel in vehicles.
What does the Zeolite catalyst do in catalytic cracking?
Lowers temp. and pressure needed for cracking to occur. Lowers costs and speeds up process.
What are the products of alkanes burning in plentiful supply of oxygen?
Carbon dioxide and water.
What are alkanes used for?
Fuels. Power and electricity.
Why are alkanes good fuels?
Most burn readily to produce large amounts of energy.
What are the products of alkanes burning in a limited supply of oxygen?
Carbon monoxide and Carbon (soot).
What happens when alkanes burn in a limited supply of oxygen?
Incomplete combustion.
Why is Carbon Monoxide poisonous?
Bonds to hemoglobin in blood and prevents oxygen bonding.
How can carbon monoxide be removed?
Catalytic converter.
What are the issues with soot?
Can cause breathing problems, make buildings dirty, and clog up engines.
How are nitrates formed?
Reacting Nitrogen and Oxygen together using an electrical spark.
How is nitrogen monoxide removed?
Catalytic converter.
What are catalytic converters made from?
A rhodium, platinum, and palladium alloy.
What can unburnt hydrocarbons and oxides of nitrogens lead to?
Photochemical smog.
Where does Ozone occur?
Troposphere.
Where do most hydrocarbons and nitrogen dioxide come from?
Cars and factories.
What is acid rain caused by?
Sulfur dioxide and oxides of nitrogen.
How is acid rain bad?
Causes damage to plants, kills fish, and causes erosion of buildings.
Is sulfur dioxide acidic or alkaline?
Acidic.
How does sulfur dioxide form acid rain?
Reacts with water in atmosphere to form sulfuric acid which falls as acid rain.
How do oxides of nitrogen form acid rain?
Dissolve in water in atmosphere to form nitric acid which contributes to acid rain.
What is wet scrubbing?
An alkali (dissolved calcium carbonate or oxide in water) is used to neutralise sulfur dioxide in flue gases. (Sprayed at acid).
What are the three main stages of Free Radical Chain Reactions?
Initiation
Propagation
Termination
What is the Initiation step in free radical chain reactions?
Free radicals are produced using visible or UV light. Called photochemical reactions. The bond breaks homolytically forming 2 free radicals.
What is the Propagation step in free radical chain reactions?
Radical reacts with non-radical molecule. New radicals are created that go on to react with other non-radical molecules. Hence - chain reaction.
What is the Termination step in free radical chain reactions?
2 radicals react to form a non-radical molecule. This ends the chain reaction.
What is the reaction to make Chloromethane?
CH4 + CL2 ——UV light—–> CH3Cl + HCl
What do free radical substitution reactions with alkanes make?
Halogenoalkanes.
What are the three Propagation step to make chloromethane from methane and chlorine?
- Cl radical reacts with methane molecule to make a methyl radical *CH3.
- Methyl radical reacts with Cl2 molecule forming chloromethane and a *Cl radical.
- Cl radical can react with more methane.
If there is an abundance of *Cl, what sort of haloalkanes will form?
di, tri, tetra.
What are alkenes?
Unsaturated hydrocarbons with at least one C=C double bond.
What is the general formula for alkenes?
C(n) H(2n)
What sort of alkenes does the general formula work for?
Only alkenes with one C=C double bond.
What sort of reactions can alkenes undergo?
Addition reactions.
What are double bonds a region of?
Electron density.
What does electron density affect?
Reactivity. High electron density = more reactive.
What species are alkenes attacked by?
Electrophiles.
What is an electrophile?
An electron pair acceptor. They are deficient in electrons and are attracted to double bonds.
What are two examples of positive ion electrophiles?
H+ and NO2^+
Where does the curly arrow go in an electrophilic addition reaction?
From the double bond to the electrophile.
What are two examples of polar molecules that are electrophiles?
H-Br and H2SO4
What is a test for alkenes?
The decoloration of Bromine water.
What happens when Bromine water is added to an alkene?
A color change from orange-brown to colorless.
What is the electrophile in the bromine water test for alkenes?
Bromine.
What is the product of the bromine water test for alkenes?
dibromoalkane.
What is the intermediate in the bromine water test for alkenes?
A Carbocation intermediate with structural formula BrCH2CH2 with a + charge on the last Carbon atom.
Why does Bromine break the double bond in an alkene?
The Br-Br molecule becomes polarized and one Br molecule has a delta positive charge and the other Br molecule has a delta negative charge. The electron pair in the double bond is attracted to the delta positive Br which breaks the double bond to bond to the Br.
What does the hydration of alkenes produce?
Alcohols.
What is needed to produce alcohols from alkenes?
Steam and an acid catalyst (H+)
What is an acid catalyst that can be used in the hydration of alkenes?
Phosphoric acid. H3PO4
Is an alkene hydration reaction reversible?
Yes.
What is hydrogenation?
Adding Hydrogen to a double bond.
What is hydration?
Adding water.
What happens to the H2 when it comes close to an alkene?
It has an induced dipole and becomes polarized. One H has a delta positive charge an the other H has a delta negative charge.
What does a hydrogenation of an alkene produce?
An alkane.
Why does the double bond in an alkene break during a hydrogenation reaction?
The electron pair in the double bond is attracted to the delta positive Hydrogen and forms a bond. This breaks the H-H bond and the double bond.
What is the intermediate in a hydrogenation reaction with an alkene?
A Carbocation intermediate where one of the carbons has a positive charge and is only bonded to 1 carbon and 2 hydrogens.
What do alkenes and hydrogen halides form?
Halogenoalkanes.
What is an example of an alkene + hydrogen halide addition reaction?
HBr + C2H4 —> C2H5Br
How many products does reacting hydrogen halides and unsymmetrical alkenes produce?
2 different products.
What is the relationship between alkyl groups bonded to the carbocation and stability of the intermediate?
The more alkyl groups bonded to the carbocation, the more stable the intermediate is.
Why do alkyl groups stabilize the carbocation?
Alkyl groups push electrons towards the positive carbocation, stabilizing it.
Do more stable carbocations or less stable carbocations form more often?
More stable.
What determines the amount of the 2 different products in an unsymmetrical alkene + hydrogen halide reaction?
The stability of the carbocation intermediate.
How many R groups are on a primary carbocation?
1
How many R groups are on a secondary carbocation?
2
How many R groups are on a tertiary carbocation?
3
Order the carbocations from most to least stable: primary, secondary, and tertiary.
Tertiary, secondary, and primary.
What is the minor product when Prop-1-ene reacts with HBr?
1-bromopropane.
What is the major product when Prop-1-ene reacts with HBr?
2-bromopropane
Why is the major product formed more often than the minor product in a reaction between an unsymmetrical alkene + hydrogen halide?
The major product comes from a secondary carbocation which is more stable than the primary carbocation. Since the secondary carbocation is more stable, it forms more often, so the major product forms more often than the minor product.
What is Markownikoff’s rule?
The major product when we add a hydrogen halide to an unsymmetrical alkene is where the hydrogen adds to the carbon with the most number of hydrogens attached already.
What can alkenes be oxidized using?
Acidified manganate (VII) ions.
What affects the oxidation of alkenes reaction?
The temperature and the strength of the oxidizing agent [O].
What does an oxidation alkene reaction using cold, dilute acidified manganate (VII) ions produce?
A diol.
What does this reaction produce ? ethene + water (steam) —cold, dilute acidified manganate (VII) ions—–> …
1,2 -dihydroxyethane
What is a diol?
A group with 2 -OH groups.
What does an oxidation ethene reaction using hot, concentrated acidified manganate (VII) ions produce?
A variety of products dependent on what groups represent R1, R2, R3, and R4 in ethene.
If all 4 R groups are alkyl, we make a ketone formed. If one of the R groups is a hydrogen, an aldehyde is formed.
What is a carbonyl group?
C=O
What can an aldehyde be oxidized further into?
A carboxylic acid.
What is produced when an alkene is oxidized using hot, concentrated acidified manganate (VII) ions and both R (hydrogen) groups are on the same side of the double bond?
An aldehyde is formed that easily oxidizes to carbon dioxide and water.
What are the conditions for hydrogenation of an alkene?
Nickel/Platinum Catalyst
