OCR CHEMISTRY UNIT 2

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.

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

Primary and Secondary alcohols can be oxidised using an oxidation agent e.g. solution containing acidified dichromate ions. changes colour from orange to green

when oxidised:

Primary alcohol turns into aldehydes,

Secondary alcohol turn into ketones

Tertiary is resistant

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.

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

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

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

 % yield=actual amount in mol of product/theoretical amount in mol of product=ans

ansx100=percentage yield

Atom Economy=Molecular mass of desired prod/sum of molecular mass of all prod

=ans x100

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)

Enthalpy Profile Diagram- diagram for a reaction to compare the enthalpy of the reactants with the enthalpy if the products

Endothermic reaction: 

• enthalpy is negative
• heat is given out to the surroundings
• reacting chemicals lose energy
• heat loss by chemicals=heat gained by surroundings

Exothermic Reaction:

• 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 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.