C6.2 Organic Chemistry Flashcards
What are hydrocarbons:
= compounds that contain only hydrogen atoms & carbon atoms
Name hydrocarbons:
- alkanes
- alkenes
Derivative hydrocarbons:
- alcohols
- carboxylic acids
Homologous series:
a family of hydrocarbons with similar chemical properties who share the same general formula
Why do alkenes, alkanes, alcohols & carboxylic acids all form their own homologous series?
- same general formula
- each successive member differs by a CH2 group (ALL)
- same functional group (NOT ALKANES)
- similar chemical reactions
Why are all alkanes saturated?
= carbon atoms joined together by single covalent bonds, no atoms can be added
(C-C bonds)
(Part of alkanes homologous series)
General formula of alkanes:
= C H
n 2n+2
Names of alkanes in order:
Methane Ethane Propane Butane Pentane Hexane Heptane Octane
How do alkanes react
= combustion, react with oxygen in air & burn
What molecules undergo combustion (complete/incomplete)?
- alkenes
- alkanes
- alcohols
Complete combustion:
If there is a plentiful supply of oxygen/air
- carbon atoms oxidised to carbon dioxide
- hydrogen atoms oxidised to water
(Products = CO2 & H2O)
Incomplete combustion
If there is a poor supply of oxygen/air
- hydrogen atoms oxidised to water
- carbon atoms oxidised to carbon monoxide, or not oxidised at all
(Products = CO, C, H2O)
Why is incomplete combustion not good?
= carbon monoxide (CO) is formed
- it’s a toxic gas & can cause suffocation
General formula of alkenes:
= C H
n 2n
Why are alkenes unsaturated?
= contain carbon-carbon double covalent bond, more atoms can be added
(C=C bond)
(part of alkene homologous series)
Name of alkenes in order:
Ethene Propene Butene Pentene Hexene
(NO METHENE)
Why does methene not exist?
Because the formula would be CH2, and there can’t be 1 carbon because it has to contain a carbon-carbon double bond so alkenes must contain at least 2 carbons
How do alkenes react? (1)
- = combustion, burn in oxygen/air (incomplete/complete)
What allows alkenes to take part in a wider range of reactions?
= alkenes have a functional group = carbon-carbon double bond
It lets alkenes undergo addition reactions
What is a functional group?
= an atom, group of atoms, or type of bond in a molecule that determines the chemical reactions of an organic compound
What do alkenes react with in addition reactions?
- bromine, to form colourless ‘dibromo’ compounds
- hydrogen, in the presence of a nickel catalyst, to form alkanes
What are addition reactions?
= an atom or group of atoms combines with a molecule to form a larger molecule, with no other product
Example of an addition reaction between an alkene and bromine:
Ethene + Bromine —> Dibromoethane
C2H4 + Br2 —> C2H4Br2
(C=C bond in ethene, C-C bond in dibromoethane)
Example of an addition reaction with an alkene & hydrogen:
Ethene + Hydrogen —> Ethane
C2H4 + H2 —> C2H6
How can we test if a substance is an alkane or alkene?
= test for unsaturation: bromine react with alkenes but no alkanes
- bromine water is orange-brown, turns colourless when mixed with alkenes, remains same with alkanes
general formula of alcohols:
C H OH
n 2n+1
Name alcohols in order:
Methanol Ethanol Propanol Butanol Pentanol Hexanol
What is the functional group for alcohols?
What extra reactions does it allow alcohols to undergo?
= hydroxyl group, -OH
= can be oxidised to form carboxylic acids
(usually only the hydroxyl group take part in the reactions, not other atoms in alcohol)
General formula of carboxylic acids:
C H COOH
n(-1) 2n+1
(-1 from first carbon atom as carbon atom in carboxyl group, eg. Pentane = C4H9COOH)
Functional group of carboxylic acids:
= carboxyl group, -COOH
name carboxylic acids in order:
= -anoic acid Methanoic acid Ethanoic acid Propanoic acid Butanoic acid Hexanoic acid
How are carboxylic acids made?
= formed when alcohols react with oxidising agents
potassium manganate (VII) solution
How can you show ethanol can be oxidised to ethanoic acid?
- add some oxidising agent to test tube of ethanol
(Oxidising agent = potassium manganate(VII) solution, KMnO4(aq), acidified with a little dilute sulfuric acid) - warm it in a water bath
= manganate (VII) ions —> reduced to manganese(II) ions
Colour change = purple —> very pale pink
Precautions of ethanol —> ethanoic acid pratical:
- eye protection
- stir reaction carefully, can be violent
both reactions carry hazard warnings
- ethanol = harmful & flammable
- potassium manganate(VII) solution = harmful & stains hands/clothes
How do carboxylic acids react?
= weak acids, so reactions typical of acids
React with:
- metals —> salts & hydrogen
- alkalis & bases —> salts & water
- carbonates —> salts & water & carbon dioxide
What is crude oil? How is it made?
= a fossil fuel, complex mixture of hydrocarbons (mostly alkanes)
Formed from remains of marine organisms alive millions of year ago, became buried in sea bed, chemical reactions turned them into crude oil
What type of source is crude oil & why?
= finite resource, being made extremely slow/no longer being made
- non-renewable source, being used up faster than being formed, will run out one day
How are the hydrocarbons in crude oil separated from each other?
Why does it work?
= fractional distillation
- works as different alkanes have different boiling points
What if the trend of boiling points in alkane molecules?
More carbon atoms in alkane molecule
= larger molecules
= stronger intermolecular forces
= higher boiling point
Describe fractional distillation of crude oil:
- crude oil heated & its vapours piped into bottom of fractionating column
(Fractionating column has temp gradient, hot at bottom & cold at top 25º-350º) - vapours cool as they rise through column
- vapours condense to liquid state if reach a part cool enough (depending on boiling point)
(Separated parts of crude oil = fractions, each contains many substances with similar boiling points)
Describe how different substances leave the fractionating column during the fractional distillation of crude oil:
- bitumen has highest boiling points, leaves at bottom of column, solid state at room temp
- refinery gases-LPG(methane, ethane, propane, butane) have lowest boiling points, reach top & leave without cooling & condensing
- other fractions (petrol, paraffin, diesel, heating oil, fuel oil) in liquid state at room temp, fall into trays & leave from middle of column
What is cracking?
= chemical reaction that converts large alkane molecules into smaller alkane molecules & alkene molecules
Eg. Octane —> hexane + ethene
C8H18 —> C6H14 + C2H4
Describe how cracking works:
Oil fractions are heated to a high temp (600-700ºC) & passed over a hot catalyst of alumina/silica
= some covalent bonds between atoms in large alkane molecules break
Conditions needed for cracking
- high temps
- catalyst
Where is cracking carried out?
- on huge scale in oil refineries
- on small scale in laboratory using pieces of broken pot as catalyst
Why do we not want fractions with relatively large alkanes molecules?
= have high boiling points
= do not flow easily & difficult to ignite
= not useful as fuels
Why do we want fractions with relatively small alkane molecules?
= have low boiling points
= flow more easily & easier to ignite
= useful as fuels
What does fractionally distillation produce?
- more fractions with large molecules & high boiling points, can be sold
- not enough fractions with small molecules & low boiling points
Why is cracking done?
= helps oil refinery match its supply of useful products in demand (petrol)
- as it breaks down the large alkane molecules into small alkane molecules in demand
- produces alkenes = useful for making polymers
Why is crude oil important?
- 90% used to produce fuels (LPG, Petrol, Diesel, Paraffin)
- remainder used as feedstock for chemical industry (alkenes make polymers)
(vital to modern lives, cant be replaces easily)
What are addition polymers?
= formed by the addition reactions between monomer molecules joined together
Why can all alkene molecules act as monomers for addition polymers?
= they contain a carbon-carbon double bond & are unsaturated
Conditions needed for addition polymerisation?
- high pressures & temps
- a catalyst
Example of addition reaction with Ethene:
= many ethene molecules join together to form poly(ethene) / polythene
Polymer used to make plastic carrier bags
Biological polymers:
- DNA molecules
- Protein molecules
- Carbohydrates
DNA molecules:
= polymers made from monomers called nucleotides
- nucleotides join together end to end to form single strand of DNA
- deoxyribose from 1 nucleotide bonds with phosphate group from the next
- 2 strands of DNA spiral round one another in opposite directions
- intermolecular forces = hydrogen bonds form between bases on opposite strands, hold strands together
Protein molecules:
= polymers made from monomers called amino acids
- each amino acid has reactive functional group at each end, join end to end to make long protein molecules
- different protein molecules contain different numbers of amino acids joined together in different combinations
Carbohydrates:
= compounds of carbon, hydrogen, oxygen, include simple sugars (deoxyribose) & complex carbohydrates (starch)
- sucrose made from 2 sugars (glucose & fructose)
- starch consists of many simple sugar molecules joined together (polymer)
What are condensation reactions?
= two molecules react together to form one larger molecule & one smaller molecule
= called condensation as smaller molecules are often water
What is the ester group
-COO-
What is the amide group
-CONH-
Show condensation reactions between carboxylic acids & alcohols:
Carboxylic acid + alcohol —> ester + water
Carboxyl group (-COOH) reacts with hydroxyl group (-OH), remaining parts of carboxylic acid & alcohol joined by ester group (-COO-)
Eg. Ethanoic acid + ethanol —> ethyl ethanoate + water
CH3COOH + C2H5OH —> CH3COOC2H5 + H2O
What must a monomer molecule for a condensation polymer have?
= 2 different functional groups, one at each end
Why are proteins condensation polymers?
= polymers formed from amino acids
= each amino acid has 2 different functional groups:
- amino group (-NH2)
- carboxyl group (-COOH)
Amino group of 1 molecule reacts with carboxyl group of another, organic product formed still has both functional groups so chain continues
- remaining parts of each monomer joined by amide group (-CONH)
What are the 2 main types of artificial condensation polymers?
- polyesters
- polyamides
What are polyesters made from?
- a carboxylic acid with 2 carboxyl groups
- an alcohol with 2 hydroxyl groups
Called polyesters as contain many ester groups (-COO-)
Eg. PET (make clothes, bottles)
What are polyamides made from?
- carboxylic acid with 2 carboxyl groups
- amine with 2 amino groups
Called polyamides as contain many amide groups (-CONH)
Eg. Nylon (make clothing/carpets)
Conditions needed for condensation polymerisation:
- no catalyst needed
- room temp & pressure
(So can be made in school, anywhere)
Chemical cell:
Eg= batteries used in portable devices (torch)
How does a chemical cell work?
- exothermic reactions in cell develop a P.D/voltage between its 2 ends
- when cell is connected to electrical circuit, current flows through cell & components of circuit
When do chemical cells stop working?
= one of the reactants is used up
- cell goes flat, can no longer provide a P.D/voltage
What was the first chemical cell, who made it, when?
- Daniell cell,
- by John Daniell
- 1836
Materials needed to make a Daniell cell:
= 2 metals: Zinc, Copper (strip)
= 2 electrolytes: Zinc Sulfate, Copper(II) Sulfate
Making a Daniell cell:
- Pour zinc sulfate solution into breaker & dip zinc strip into it
- Pour copper(II) sulfate solution into another breaker & dip copper strip into it
- Connect the 2 solutions using filter paper soaked with potassium nitrate solution
- Connect voltmeter to metal strips to measure P.D/voltage
How does a fuel cell work?
= produces electricity through a chemical reaction between a fuel and oxygen, without combustion happening
Precautions in Daniell cell making:
- Take care with reactant solutions as can be harmful at some concentrations (zinc sulfate solution, copper(II) sulfate solution)
- Wear eye protection
How does a hydrogen-oxygen fuel cell work, why is oxygen and hydrogen used?
Hydrogen reacts with oxygen in an exothermic reaction to produce water vapour:
2H2(g) + O2(g) —> 2H2O(g)
Same overall reaction happens in a hydrogen-oxygen fuel cell, but its separated into 2 reactions, 1 on each side of cell
2 reactions in a hydrogen-oxygen cell:
- Hydrogen molecules lose electrons & become hydrogen ions
2H2(g) —> 4H+(aq) + 4e-
Hydrogen ions pass through a ‘proton exchange membrane’ to other side of fuel cell & electrons travel through external circuit to other side of fuels cell
- hydrogen ions combine with oxygen & electrons at other side to form water vapour
4H+(aq) + O2(g) + 4e- —> 2H2O(g)
