7-Hydrocarbons Flashcards
Formula for alkenes
CnH2n
Formula for alkanes
CnH2n+2
Methane
CH4
Ethane
C2H6
Propane
C3H8
Butane
C4H10
CH4
Methane
C2H6
Ethane
C3H8
Propane
C4H10
Butane
Functional group -coo-
Esters
Functional group -cooh
Carboxyl group- carboyxilic acid
Functional group -oh
Hydroxy(l)- alcohols
Carboxylic acid
Weak acids
Functional group -cooh- carboxyl
Esters
Orgaic compounds, fruity smell, -coo- functional group
Alcohols
Functional group -oh
Used as fuel,
reacts with metals to form metal ethanoate,
soluble in water (decreases as chain size gets greater- becomes less miscible),
oxidise without combustion to form carboxylic acids
Uses of alcohols
Methanol-chemical feedstock,
ethanol-alcoholic drinks, fuel, solvent(can dissolve organic and inorganic substances), propanol and butanol-fuel and solvent
Fermentation
Produces alcohol, sugar dissolved in water mixed with yeast, air lock needed to allow co2 out but no air in, warm temp 25-35 C, yeast dies when ethanol conc reaches 15%
O2 causes ethanol to oxidise into ethanoic acid- vinegar test
What happens if air is present during fermentation
The o2 causes ethanol to oxidise into ethanoic acid- vinegar taste
Crude oil
- Finite resource
- mixture of hydrocarbons
- formed over millions of years from once living marine plants/animals
Fractions
Mixture of hydrocarbons w/ similar boiling points
As increase in chain length of hydrocarbons
- bp increases
- volatility decreases
- viscosity increases
- flammability decreases
Alkenes
- CnH2n
- unsaturated- contain less hydrogen atoms than alkane w/ same number of carbon atoms
- contains atleast one double bond
Homologous series have
- same general formula
- successive member differ by CH2 unit
- gradual variation in physical properties eg. Bp
- similar chemical properties
Alkenes reactions
- v. Reactive due to presence of C=C bond
- undergoes addition reactions
- in addition reactions C=C becomes C-C
- allows other atoms to jioin across C-C
- in functional group C=C
- burn (but rarely do so)
- too valuable or making polymers
- incomplete combustion w/ small flames
Testing for alkenes and alkanes
- mix w/ orange brown bromine water
- alkane- stays orange
- alkene- decolours - br-br molecule no longer present, has joined alkene molecule
Alkenes + halogens
Produce haloalkenes
Eg. Chlorine, bromine, iodine
-usually spontaneous reactions
Hydrogenation
Alkene + hydrogen = alkane
- (nickel) catalyst
- 60-150 C each double bond needs one H2 molecule to hydrogenate
- staigtenes molecules and incrreases melting points
- make spreadable margarine
Hydration
Alkene + water = alcohol
- temp approx 300 C
- catalyst
- requires energy to heat gases to generate high pressure
- unreacted ethane and steam recycles over catalyst - reversable reaction
Addition reactions
- molecule combines w/ another molecule forming one larger molecule + no other products
- alkanes cannot take part
Addition polymerisation
- ethene/alkene monomer
- poly(alkene) polymer
- c=c in alkene allows molecules to join yogether to form a single product
Combustion of alkenes
- test ethene gas w/ lighted splint
- alkenes burn with a smokier yellow flme Compared to alkanes
- alkenes relese less energy per mole in combustion that alkanes
- alkenes not used as fuels
Complete combustion
Alkene + oxygen = carbon dioxide + water
Polymers
- long chain molecuules
- natural eg. Dna
- man-made -plastics
- made by joining together thousands of small identical molecules (monomers)
- two diff types:
- condensation
- addition
Addition polymers
- monomers are alkenes
- monomer has a C=C bond but polymers have C-C
Fractional distillation
- hydrocarbons in crude oil seperayed. Into fractions
- each contains molecules with a similar number of carbon atoms
- by fractional distilation
- each contains molecules with a similar number of carbon atoms
- fractions can be processed to produce fuels and feedstock for petrochemical industry
Crude oil produces
- petrol
- diesel oil
- kerosene
- heavy fuel oil
- liquified petroleum gas
Petrochemical industry produces useful materials such as.
- solvents
- lubricants
- polymers
- detergents
-vast array of natural and synthertic carbon compounds occur due to ability of carbon atoms to formfamily of similar compunds
Properties of polymer depend on
- monomer made from
- condition under joined together
Low density poly(ethene)
- very high pressure
- trace of o2
- polymer chain branched
- randomly arranged
- flexible, unreactive, made into fibres, carrier bgs, bubble wrap
High density poly(ethene)
- catayst at 50 C
- slightly raised pressure
- less branching
- line up closer- straigter molecules
- higher softening tmp, stronger than LD
- strong, flexible, resitsts shattering, chemical attack
- plastic, bottles,pipes, bucket
Thermosoftening polymers
- melt when heated
- most do
- can be recycled
- dont ahve caovalent bonds between neighboring polymer molecules
- molecules can move over each other when heated- melts
- weak intermolecular forces
- when cools- intermolecluar forces bring polymer molecules back together -polymer hardens again- can be remolded
Thermosetting
- dont melt
- char and burn
- resistant to much higher temp
- electrical plugs- dont want to melt
- cross links- covalent bonds between molecules
Condensation polymerisation
-monomers dont need C=C
-instead have two diff functional groups
-smaller moolecule (usually water) produced as by product
-eg. Polyester-naturally occur as biologicalpolymer
or -made artificially
-simple polyester
-monomer- as hydroxyl (O-H) groups
-another monomer w/ two carboxylic acid groups (-COOH)
-symbols may be used to represent middle of each monomer
-only funtcional group at end cause reaction to take place
Examples of biolgical polymers
- DNA
- protein
- starch
- cellulose
DNA
- double helix
- two polymer chains lined up and twisted around each other
- four diff types monomers
- nucleotides (CGAT)
- sequence of nucleotides along DNA molecule -cofe for gene
Protein
- biological polymers inside cells
- amino acids- monomers
- eg. Enzymes
- amino acids
- atleast two functional groups
- NH2 and -COOH
- atleast two functional groups
- polymers in cells- polypeptide and protein
- condensation polymerisation
- each monomer added, growing polymer chain, water molecule produced
Starch and cellulose
- made by plants
- monomers sugar/glucose molecules
- starch-storing enegry as complex carbs
- cellulose- strong cell wall
- gives plant cells strength
Making ethanol
- alcohol in beer and other alcoholic drinks
- fuel for vehicles on own or mixed with petrol
- can be produced by
- fermentation and concentrated with fractional distillation -hydrating ethene0 less green as cracking crude oil
Combustion of alcohol
Complete
Alcohol+O2 = CO2 +H20
Incomplete
Alcohol +O2=C02 +CO+C+H20
Reaction of sodium and alcohol
Sodium + ethanol = sodium ethanoate +H2
Alcohol solubility with water
- short hydrogen chains (MEP) added to water mix easily to priduce solution
- solubilty dexreases as length of molecule gets longer -may not mix easily, two distinct layer may be left in container
Alcohols oxidise
-to prouce carboxylc acids
-oxidising agent (O)
Ethanol + oxidising agent [O] = ethanoic acid + water
Catalytc crackng
550C
Catalyst
Steam cracking
Over 800C
No catalyst
