- Created by: java33
- Created on: 12-04-11 13:20
Making ethanol-1.Hydration of ethene C2H4 2.Fermentation of sugars
Hydration-catalytic hydration of ethene, using steam, phosphoric acid catalyst H3PO4. CONDITIONS: High temperature, moderate pressure. Reaction is reversible
Fermentation- Carbohydrates converted into ethanol and CO2. Sugar or starch used as Carbohydrate
Ethanol produced is 14% conc
CONDITIONS:-Low temperatures, yeast present is catalyst.(enzyme) at low temp slow (25o) but above 37o then enzyme denatures, also cannot work at above conc of 14%
Anaerobic reaction does not need O2 Must be kept away from air as undesireable products may be produced such as ethanal or ethanoic acid.
Ethanol used in alcohol beverages, perfume, aftershave, cleaning fluids
Ethanol in alcoholic beverages are fermented
used also as a fuel blended with peteroleum
Used in methylated spirits
Uses of methanol-clean burning fuel used as additive in high performance racing cars.
Properties of Alcohols
Volatility and boiling points- have hydrogen bonds so relatively high melting and boiling point. Presence of H-Bonds results in lower volatility (ease of turning liquid to gas)
Solubility- alcohols dissolve in water because of H-bonds form between polar -OH group in water and alcohols. Solubilty decreases as chain length increases, large part of the alcohol molecule is made up of a non-polar hydrocarbon chai, Hydrocarbon chain does not form H-bonds with water.
Primary alcohol- OH group attached to C atom with no alkyl group or bonded to one alkyl group
Secondary alcohol -OH group attached to C atom bonded to two alkyl groups
Tertiary alcohol- -OH group attached to C atom bonded to three alkyl groups
Combustion and Oxidation of Alcohols
Primary and Secondary alcohols can be oxidised using an oxidation agent e.g. solution containing acidified dichromate ions. changes colour from orange to green
Primary alcohol turns into aldehydes,
Secondary alcohol turn into ketones
Tertiary is resistant
Esterfication and Dehydration of alcohols
Reaction of an alcohol with a carboxylic acid to produce an ester and water. also in presence of an acid catalyst. e.g. sulfuric acid
The OH bond in the alcohol is broken and water is formed. Water molecule comes from the OH of the carboxylic acid group and the H in the alcohol group.
Preparing an ester-boling tube same amount of carboxylic acid and alcohol, drops of conc H2SO4. Boiling tube in water bath of 80o 5mins. Pour contents into beaker or cold water. Oil is the ester.
Dehydration-elimination reaction in which water is removed from saturated molecule to make and unsaturated molecule.
Formed an alkene in present of acid catalyst e.g. conc sulfuric acid, conc phosphoric acid.
Alcohol heated under reflux in presence of phosphoric acid for 40mins
Halogens are more electronegative then carbon atoms, so bonded electron pair is attracted to the halogen atom.
Electronegativity decreases down the group decrease in polarity
Halogenoalkanes react with nucleophiles in substitution reactions
Nucleophile replaces the halogen atom in halogenoalkanes forming a compound containing a different functional group.
Hydrolysis- reaction is carried out by heating under reflux.
halogenoalkanes react with aq hot hydroxide ions,e.g. sodium hydroxide
nucleophillic substitution reaction occurs product is an alcohol.
Reactions of Halogenoalkanes
Nucleophillic subs-atom or group of atoms replaced by a nucleophile(electron pair donor)
the carbon-halogen bond breaks as the two electrons in the covalent bond move to the halogen forming a -ion.
two electrons from the hydroxide ion OH-, forming a covalent bond with the carbon atom.
Rate of Hydrolysis-experiment(precipitate exp of halogens)
calculating 1/time taken for precipitate to occur
controlled test:equal amount in mol of Halogenalkane, Water bath of 50o, solution of ethanol H2O and aqsilvernitrate, place in water bath add equal sol to Halogenalkanes. Time precipitate to form
Factors affecting rate of Hydrolysis
Polarity- carbon-fluorine bond is most polar amongst the halogenalkanes so C(delta+) atom should attract nucleophile most readily and give fastest reaction
Bond Enthalpy- carbon-iodine bond weakest so should be broken easiest to give fastest reaction
-bond enthalpy is more important then bond polarity
-Rate of reaction increases from the fluoroalkanes(slowest) to the iodoalkanes(fastest) as the carbon-halogen bond enthalpy weakens
Halogenoalkanes and the enviroment
Uses- PFTE (Teflon) is polymerisation od tetrafluroethene. C-F bonds are very strong makes PFTE inert and resistant to chemical attack,
PVC-polymerisation of of chloroethene-drainpipes window frames
CFC-created for refrigerants,propellants,solvents
Limitations-Break down by UV radiation to form chlorine radicals, these catalyse the breakdown of ozone layer
Alternatives-Hydrofluroalkanes same effect but one tenth less
-Ozone friendly products do not harm ozone layer but are flammable
Percentage Yield & Atom Economy
% yield=actual amount in mol of product/theoretical amount in mol of product=ans
Atom Economy=Molecular mass of desired prod/sum of molecular mass of all prod
molecules absorb infrared radiation by bending or stretching
amount of vibration depends on: Bond strength, Bond length, Mass of each atom involved in the bond Absorbed energies displayed as an infrared spectrum
Uses of it- Drug analysis, Forensic science, Quality control in perfume, MOT
Most of organic compounds produce peak at 3000 due to absorption by C-H bonds.
3230-3500 represents an O-H group in alcohols
1680-1750 represents C=O bond in aldehydes and ketones
2500-3300 is very broad and indicates presence of the O-H group in carboxylic acid. Strong sharp peak at 1680-1750 represents the C=O group in a carboxylic acid.
Uses- identify unknown compounds, Determine abundance of each isotope in an element. Gain further information about the structure and chemical properties of molecules.
Examples- Monitoring the breath of patients during surgery whilst under anesthetic, Detecting banned substances such as steroids, Detecting toxic chemicals in contaminated marine life,
Graph- (m is the mass, z is the charge on the ion (m/z))-x axis, percentage abundance- y-axis
use relative atomic mass to work out
Enthalpy-is the heat content that is stored in a chemical system
The chemical system is the reactants and products. The surroundings are what is outside the chemical system
Exothermic- products are smaller than reactants resulting in heat loss (-ve)
Endothermic- Products are larger than the reactants resulting in heat gain from surroundings (+ve)
Exothermic and Endothermic Reactions
Enthaply Profile Diagrams
Enthalpy Profile Diagram- diagram for a reaction to compare the enthalpy of the reactants with the enthalpy if the products
- enthalpy is negative
- heat is given out to the surroundings
- reacting chemicals lose energy
- heat loss by chemicals=heat gained by surroundings
- enthalpy is positive
- heat is taken in from surroundings
- reacting chemicals gain energy
- heat gained by chemicals=heat loss by surroundings
Is the minimum energy required to start a reaction by the breaking of bonds
important to show the activation energy and enthalpy change using arrows pointing in the correct direction
- the activation energy is positive and the arrow points up
- the reaction is exothermic with heat energy being lost to the surroundings so the arrow goes down.
Activation energy is always the input of energy from reactants to the top of the energy barrier.
Standard Enthalpy changes
Standard conditions are:
- A pressure of 100kPa
- a stated temperature (25o)
- A concentration of 1 mol dm^-3
Standard State is the physical state of a substance under the standard conditions of 100kPa and 25o
Standard enthalpy change of a reaction molar quantities expressed in a chemical equation under standard conditions and reac&prod are in standard states
Standard enthalpy change of combustion:enthalpy change that takes place when 1mol of a substance reacts completely with oxygen under standard cond and reac&prod in standard states
standard enthalpy change of formation:when 1mol of a compound formed from elements under standard cond and state.