C6.2 Organic Chemistry Flashcards
Hydrocarbons
Compounds that only contain hydrogen atoms and carbon atoms
Release carbon dioxide when burnt
Example: coal
Alkanes
Hydrocarbons
Saturated - each carbon is bonded to another carbon by a single covalent bond
General formula CₙH₂ₙ₊₂
Names ending in “ane”
First 5 alkanes
. H
. |
Methane CH4 : H - C - H
. |
. H
. H H
. | |
Ethane C2H6 : H - C - C - H
. | |
. H H
Propane C3H8
Butane C4H10
Pentane C5H12
How many bonds can carbon atoms form
Up to 4
How many bonds can hydrogen atoms form
Only 1
How alkanes react
Combustion when alkanes react with oxygen in the air and burn
If plentiful supply of oxygen or air complete combustion happens:
carbon atoms oxidised to carbon dioxide, hydrogen atoms are oxidised to water
Example: propane + oxygen -> carbon dioxide + water
If poor supply of oxygen or air incomplete combustion happens instead
alkane + oxygen → carbon monoxide (CO) + water
problem because carbon monoxide is toxic gas and can cause suffocation
Some carbon atoms may not be oxidised at all and released as carbon particles.
CLEAN FLAME PRODUCED
Alkenes
Hydrocarbons
Unsaturated: Contain a carbon - carbon double covalent bond, C=C that can open up in reactions and bond
General formula CₙH₂ₙ
First 4 alkenes
METHENE DOES NOT EXIST!!!
. H H
. | |
Ethene: C2H4: C=C
. | |
. H H
Propene: C3H6
. H H H
. | | |
Butene: C4H8 : H-C-C-C=C
. | | | |
. H H H H
Pentene: C5H10
EACH CARBON ATOM MUST HAVE NO MORE THAN 4 ARMS
How alkenes react
alkenes can burn in oxygen or air, and the products of combustion are the same as alkanes
SMOKY DIRTY FLAME PRODUCED
alkenes have a functional group allowing them to take part in wider range of reactions
C=C is the functional group - lets alkenes undergo addition reactions where double carbon bond opens up
Addition reactions (polymerisation of alkene monomers)
atom or group of atoms combines with a molecule to form larger molecule, with no other product.
alkenes react with bromine in addition reactions forming colourless ‘dibromo’ compounds as they are unsaturated and C=C bond can open up but alkanes cannot as they are saturated with no C=C double bond
alkene + bromine → saturated, colourless dibromo-alkane compound
Example: Ethene + bromine -> dibromoethane The alkene decolourises bromine water that can be used
. to test for saturation
. C2H4 + Br2 -> C2H4Br2
. H H H H
. | | | |
H-C=C-H + Br-Br -> H-C-C-H
. | |
. Br Br
How can an alkene become an alkane
Hydrogenation - Undergo addition reactions with hydrogen in presence of nickel catalyst
Example: Ethene + hydrogen -> ethane
. C2H4 + H2 -> C2H6
C=C carbon double bond opens up to react
Alcohols in chemistry
Functional group: -OH (hydroxyl group)
General formula: CₙH₂ₙ₊₁OH
First 5 alcohols
. H
. |
Methanol: CH3OH: H-C-O-H
. |
. H
. HH
. | |
Ethanol: C2H5OH: H-C-C-O-H
. | |
. HH
Propanol: C3H7OH
Butanol: C4H9OH
Pentanol: C5H11OH
Oxidation of alcohols
(by potassium manganate)
alcohol + oxidising agent → carboxylic acid
Carboxylic acid
general formula CₙH₂ₙ₊₁COOH
functional group: -COOH (carboxyl)
Made by adding acidified (with H₂SO₄) potassium manganate solution to alcohol and warming with water bath
Colour change from purple to very pale pink as manganate ions are reduced to manganese atoms
reactions of carboxylic acids
same as any weak acid:
Carboxylic acid + metal -> salt + hydrogen
Carboxylic acid + base -> salt + water
Carboxylic acid + carbonates -> salt + water + carbon dioxide
Crude oil formation
Remains of marine organisms / organic material buried under sea bed over millions of years under high temperatures and pressures
Finite resource
Separated by fractional distillation as larger molecules have higher boiling points,
due to stronger intermolecular forces
Order of crude oil fractions (top to bottom of column)
LPG, petrol, paraffin, diesel, heating oil, fuel oil, bitumen
Cracking (chemistry)
long alkane → smaller alkane + alkene
600-700⁰C
Alumina or silica catalyst
Conditions for addition polymerisation
High pressure
Catalyst
DNA polymer
Monomers are nucleotides (strands joined by hydrogen bonding)
Protein polymer
Amino acids, each with functional group at each end (amine / amino group NH₂ and carboxyl COOH)
Amino acid structure:
. HH O
. | | ||
H-N-C-C-O-H
. |
. R
carbohydrate polymer
starch, polymer of simple sugars like glucose
carboxylic acid + alcohol reaction
carboxylic acid + alcohol → ester + water
condensation (organic chemistry)
2 molecules react to form 1 large molecule and 1 smaller (often water)
What are polyesters made from
Dicarboxylic acids and dialcohols
They are condensation polymers
Functional group: -COO-
What are polyamides made from
Dicarboxylic acids & diamines
Contain amide functional group (CONH)
conditions for condensation polymerisation
without a catalyst at room temperature and pressure
Chemical cells
Exothermic reactions produce a potential difference between the two ends
When one reactant is used up, cell goes flat
Daniell cell
Wet cell
the negative electrode (zinc in the Daniell cell, whilst copper is the positive one)
Fuel cell anode half equation
2H₂ (g) → 4H⁺ (aq) + 4e⁻
Redox reaction
proton exchange membrane
where hydrogen ions travel through to cathode, whilst electrons travel through external circuit
Fuel cell cathode equation
4H⁺ (aq) + O₂ (g) + 4e⁻ → 2H₂O (g)
Redox reaction
First 5 carboxylic acids
. O
. ||
Methanoic acid: HCOOH: H-C-O-H
. H O
. | ||
Ethanoic acid: CH3COOH: H-C-C-O-H
Propanoic acid: C2H5COOH
Butanoic acid: C3H7COOH
How do alcohols react
Burn in the air with oxygen - combustion, or incomplete combustion if lack of oxygen
Alcohol + oxygen -> carbon dioxide + water (complete combustion)
Alcohol + oxygen -> carbon monoxide + water (incomplete combustion)
Hydroxyl functional group lets alcohols undergo reactions other than combustion
eg. they can be oxidised to form carboxylic acids.
Other atoms in alcohol molecules usually do not take part in these reactions
Repeating units for addition polymers
1) Draw the monomer with bonds at 90°, if this is not given to you:
H HH H H
| | | | |
C=C-C-H -> C=C
| | | |
H H H CH3
2) Redraw the monomer but:
change double bond to single bond and draw two long bonds either side of where the double bond was
put square brackets round the diagram, passing through the outer bonds
._ H H _
| | | |
+—C-C——+
|_ | | _| n n used here to show that the unit repeats n times
. H CH3
How is nylon formed
2 monomers needed: AMIDE group, CARBOXYLIC group
Chemicals used: diaminohexane + dicarboxyllic acid
Nylon forms at interface between liquids - don’t mix
Wind it using a taper
Why petrol has a lower boiling point than diesel?
Petrol molecules are smaller than diesel molecules
Weak intermolecular forces between petrol molecules compared to diesel molecules
so less energy needed to boil
Addition polymerisation vs condensation polymerisation
Addition: 1 product (the polymer), 1 monomer
Condensation: 2 products (polymer and a small molecule like water), 2 monomers (unless amino acids)
Fuel cell
Cell supplied with a fuel and oxygen and uses energy from reaction between them to produce electrical energy
