Unit 4- Materials Revolution

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Electronegativity and Intermolecular forces

Electronegativity is the amount of pulling power the nucleus of an atom has when attracting other atoms.
Fluorine is the most electronegative element.
Electronegativity increases as you go across the periods and it decreases as you go down the groups (except noble gases).
In a polar bond, the difference in Electronegativity between 2 atoms causes a dipole.
The greater the difference in Electronegativity the more polar the bond will be.
Covalent bonds in diatomic elements e.g. H2 are non-polar.
There are 3 types of intermolecular bonds: Instantaneous dipole-induced dipole, permanent dipole- permanent dipole and hydrogen bonding.
Hydrogen bonding is the strongest, but can only occur if there is hydrogen which can bond to either fluorine, oxygen or nitrogen.
This bond is polarised and formed with lone pairs on the 3 elements.

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Amines and Amides

Amines:

Amines are organic derivatives of ammonia- one of the hydrogens in ammonia is replaced with an 'R' group.

Primary amines are surrounded by 1 of these groups, secondary 2 and tertiary 3 or more.

When naming amines, they will be 'amino', and will have a number if the alkane chain is more than 2 carbons long e.g. '2-amino propane'. If there are 2 amine groups it is a diamine so will be 'diamino'.

Amines are bases because they have a lone pair of electrons so they accept protons (H+ ions); the lone pair of electrons forms a dative covalent bond with the hydrogen ion.

An amine can be neutralised by reacting it with an acid to make an ammonium salt e.g. CH3CH2NH2 + HCl ---> CH3CH2NH3+Cl -.

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Amines and Amides continued

Amides:

Amides are similar to amines but contain a carbonyl group ( CONH2).

This group pulls electrons away from the rest of the group so amides will behave differently to amines.

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Amines can be acylated to form N-substituted amides:

This is acylation, where theacyl chloride is substituted for a hydrogen atom. 

A hydrogen atom from the NH2 group is substituted with the acyl chloride group when they react, and this reaction produces HCl as a waste product- this HCl will react with any excess amine and form an ammonium salt in the neutralisation reaction.

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Hydrolysis of Amides

Amides can be hydrolysed in 2 ways, either under acidic or basic conditions

Acididc:

You can heat DILUTE acid with an amide to get a carboxylic acid and an ammonium salt

CH3CONH2 + H2O + HCl ---> CH3COOH + NH4Cl

Basic:

You can heat DILUTE alkali with an amide to get a carboxylate ion and ammonia gas given off

CH3CONH2 + NaOH --> CH3COO - Na+ + NH3 

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Hydrolysis of Esters

Esters can be hydrolysed using either an acid or alkali to make an alcohol

Acid:

Hydrolysis with an acid splits the ester into an acid and alcohol; it is the reverse of esterification- you have to heat the ester under reflux with a dilute acid e.g. hydrochloric.

CH3CH3CH2COOH + H2O + H+ --> CH3COOH + CH3CH2OH

Base:

Hydrolysis with a base gives you a carboxylic acid salt and an alcohol; you have to heat the ester under reflux with a dilute alkali e.g. sodium hydroxide.

CH3CH3CH2COOH + NaOH --> CH3COO - Na+ + CH3CH2OH

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Organic solids- Purification by Recrystallisation

These are the steps in the recrystallisation process:

  • A very hot solvent is added to an impure solid until it just dissolves- don't add too much.
  • This gives a saturated saturation of the impure product.
  • Leave it to cool slowly- crystals will form.
  • Remove the crystals by hot filtiration- leave this too cool.
  • Then, dry the crystals- this will then leave you with more crystals which are much purer that the original, impure solid.

An appropriate solvent must be chosen for recrystallisation- the solid has to be VERY soluble when the solvent is hot, but nearly INSOLUBLE in it when it is cold.

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Polymers

Addition polymers are formed from many alkenes (monomers).

Condensation polymers are usually made up of more than one type of monomer- each monomer has at least two functional groups which react with each other to form a link.

Each time a link is formed a water molecule is lost.

Dicarboxylic acids and diamines make polyamides- amide links are formed and a water molecule is lost each time one of these links is made.

Dicarboxylic acids also react with diols, which creates polyesters- ester links are formed and a water molecule is lost each time one of these links is formed.

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Green chemistry and polymer production

Green chemistry:

  • Use reactant molecules that are as safe and friendly to the environment as possible.
  • Use as few other materials such as solvents as possible- if you have to then choose ones which don't harm the environment.
  • Use renewable raw materials whenever possible.
  • Energy usage should be kept to a minimum.
  • No waste products which are dangerous to human health or the environment should be produced
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Recycling and Reusing polymers

Recycling and reusing polymers reduces CO2 emissions as not as much fuel has to be burnt for polymer production:

Recycling & Reusing:

  • Recycling means less raw materials are used and less waste goes into land fill
  • Some plastics can be melted down into their monomers to be produced into something else
  • HOWEVER, sorting and processing does use lots of energy
  • Waste plastics can also be burned, especially the non-recycleable ones
  • Burning the plastic reduced land fill and produces heat energy which can be used to generate electricity
  • HOWEVER, this process produces lots of CO2 and some toxic waste gases
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