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Organic chemistry (O-level chemistry)
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O-level organic chemistry
Organic chemistry is the study of compounds of carbon
Uniqueness of carbon
- Carbon forms very many useful compounds with different physical and chemical properties.
Importance of organic compounds
Organic compounds are used as
- Drugs
- Perfumes
- Clothes
- Shoes
- Dyes
- Detergents for washing
- Packing materials
- Herbicide to dry weeds
Terminologies
Hydrocarbons are compounds that contain carbon and hydrogen only
Functional groups are reactive parts of organic compounds for example
Double bonds (C=C) for alkenes
Triple bonds for C ≡C) alkynes
Hydroxyl group (-OH) for alcohols
Carboxylic groups (-COOH) for carboxylic acids
Homologous series
These are a group of compounds with members related as follows
- Members have similar general formula e.g. the general formula of alkanes is CnH2n+2.
- Have similar functional groups and thus same chemical properties
- Have similar methods of preparation
- Show gradual change in physical properties for instance alkanes range from gases to liquids to solids
Alkanes
This is the simplest homologous series with saturated hydrocarbons with a genera
l formula CnH2n+2.
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Compounds with the same molecular formula but different structural formulae like butane and methylpropane are called isomers
Physical properties of alkane
- they are insoluble in water
- they are soluble in organic solvents
- they range from gases to liquids to waxy solids
Chemical properties
- They burn in air to produce carbon dioxide, water, and heat. Due to the production of heat, they are used as fuel.
Example
CH4 + 2O2 → CO2 + 2H2O + heat
- Chlorination: they react with chlorine in the presence of sunlight or u.v-light to produce chlorinated alkanes.
Example
![](https://digitalteachers.co.ug/wp-content/uploads/2020/01/4.png)
Preparation of alkanes
- By distillation of petroleum oil
- By cracking: cracking is the breakdown of long-chain hydrocarbons into useful short-chain hydrocarbons by heat (thermos-cracking) or by a catalyst (catalytic cracking)
- From Biogas: methane is the main component of biogas. Biogas is produced by anaerobic decomposition of organic matter (cow dung, feces, plant remains) in the presence of water
Alkenes
These are hydrocarbons that contain aa double bond
The general formula is CnH2n n ≥ 2
Examples are
Ethene CH2=CH2
Propene CH3CH=CH2
But-1-ene CH3CH2CH=CH2
But-2-ene CH3CH=CHCH2
Preparation of ethene
![](https://digitalteachers.co.ug/wp-content/uploads/2020/01/6.png)
By dehydration (removal of a water molecule from) of ethanol with hot concentrated sulphuric acid
Testing or ethene
- Ethene decolorizes bromine water
![](https://digitalteachers.co.ug/wp-content/uploads/2020/01/7.png)
2. Ethene decolorized bromine tetrachloromethane
![](https://digitalteachers.co.ug/wp-content/uploads/2020/01/8.png)
3. Ethene decolorizes acidified potassium permanganate (VII)
4. Alkenes form polymers called polyalkenes
A polymer is a molecule with a high molecular mass formed combination of very many small molecules called monomers.
Examples
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(ii) Propene polymerize to form polypropene
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(iii) Vinyl chloride polymerize to form polyvinylchloride (PVC)
![](https://digitalteachers.co.ug/wp-content/uploads/2020/01/11.png)
Uses of polyethene
- Insulator
- Water pipes
- Packing mate
Polymerization of dienes
Alkenes with conjugated double bond undergo polymerization to form polyalkenes with double bonds
Example
![](https://digitalteachers.co.ug/wp-content/uploads/2020/01/16-400x166.png)
Polymers from conjugated dienes have double bonds, they are elastic and constitute different forms of rubber.
Vulcanization of rubber
It is heating rubber with Sulphur to make it
- Less elastic,
- More resistant to heat
- More durable
- Easier to dye
Uses of vulcanized rubber
- For raincoats
- Boots
- Shoe soles
- Rubber bands
Natural and artificial polymers
Natural polymers are polymers made plant or animal bodies
Examples are
Polymers | monomers |
Starch | glucose |
Cellulose | glucose |
Protein | Amino acids |
Cotton | |
Wool | |
silk | |
sisal |
Artificial polymers are polymers that are man-made
Examples
Nylon a
Polyester
Polyethene
Advantage of natural polymers
- Cheap
- biodegradable
The disadvantages of natural polymers
- not durable
- have low property value such as low tensile strength
Advantage of synthetic polymers/plastic
- light and portable
- resistant most chemicals
- they are durable
- they are thermos insulators
The disadvantage of synthetic polymers
- they are nonbiodegradable
- fire hazards
Thermoplastic and thermosetting polymers
Thermoplastic polymers are those that soften and can be remoulded into new shapes. E.g. polyethene
Thermosetting polymers are those that decompose on heating and cannot be remoulded on heating for example vulcanized rubber, melamine, Bakelite.
Alkyne
They are hydrocarbons with a general formula CnH2n-2, n. They contain a triple bond
Examples
Ethyne HC≡CH
Propyne, CH3C≡ CH
But-1-yne CH3CH2C≡ CH
But-2-yne CH3C≡ CCH3
Like alkenes they decolorize bromine water
Alcohols
They are compounds that contain hydroxyl (-OH) group.
Example
Ethanol or CH3CH2OH
Preparation of ethanol
By fermentation of glucose or starch-containing food (cassava, maize, and bananas)
![](https://digitalteachers.co.ug/wp-content/uploads/2020/01/14.png)
Uses of ethanol
Social drink
Antiseptic in soft drinks
Production of ethene
Fuel
Extraction of sugar
- sugar canes are crushed and juice extracted
- Sulphur dioxide is bubbled through to breach the juice
- Lime is added to clarify the juice and adjust pH and filtered
- The juice is boiled to increase its concentration from 15% to 60%.
- Sugar crystals in ethanol are added to crystalize sugar
- The sugar crystals are washed with water and dried
The reaction of sugar with sulphuric acid
Sugar is dehydrated with concentrated sulphuric acid with the evolution of heat to a black mass of carbon
![](https://digitalteachers.co.ug/wp-content/uploads/2020/01/15.png)
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