A2 Unit 4 AQA Chemistry Notes

These notes were made to be used with the AQA A2 textbook the large gaps are for diagrams and processes which are in the textbook you just need to add them.

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  • Created on: 24-05-12 19:24
Preview of A2 Unit 4 AQA Chemistry Notes

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Chemistry Revision
Unit 1
Key Words
Acids and Bases
Nomenclature and Isomerism in Organic Chemistry
Aromatic Chemistry
Amines
Amino Acids
Polymerisation
Organic Synthesis and Analysis
Structure Determination
Chromatography

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Page 2

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Acids, bases and buffers
Defining an acid
An acid is a substance that can donate a proton (H+ ion)
A base is a substance that can accept a proton (H+ ion)
Ionisation of water
Water is slightly ionised, and this becomes an acid base reaction where one water molecule donates a proton to another
o Equilibrium established in water and all aqueous solutions
Equilibrium expression
The concentration of water is constant and is added into a new equilibrium constant
o KW = [H+][-OH]
This is…read more

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This doesn't mean that the water is acidic as the H+ has the same concentration of -OH so is
neutral
Working with the pH scale
Finding [H+] from pH
o pH = -log[H+]
pH= 3.00
Therefore, 3.00 = -log[H+]
o So, - 3.00 = log[H+]
Anti log of this, 10-3.00 = [H+]
[H+] = 1.0 × 10-3moldm-3
Finding [-OH] from pH
o For bases there are two steps
Step 1
pH = -log[H+]
pH = 10.00
o 10.00 = -log[H+]
-10.…read more

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Start] 1.00 0.00 0.00
[ m] 1.00 - [CH3COO-] [CH3COO-] [CH3COO-]
For this we assume that the degree of dissociation is that small that 1.00 - [CH3COO-] 1.00
2
[H+]
o Ka = 1.00
[H+] =
K W ×[HA] = 4.12 x 10-3moldm-3
pH = -log 4.12 x 10-3moldm-3 = -2.385 => 2.…read more

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From the equation, number of moles of H2SO4 = 0.5 number of moles of NaOH
So number of moles of H2SO4 = 15.0 × 1000 B
o Therefore B = 0.…read more

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Therefore pKA = pH
Buffer Solutions
Buffers are solutions that can resist changes of acidity or alkalinity, when small amounts of acid or alkali are added to them
their pH remains almost constant
o Buffers are designed to keep the concentration of H+ and -OH almost unchanged
They are based on an equilibrium reaction which will move in the direction to remove either additional
hydrogen or hydroxide ions if these are added
Acidic Buffers are made from weak acids, they work because the dissociation of…read more

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The same equilibrium reaction acts to buffer the acidity of
soils
o There are buffers in everyday products such as detergents and shampoos to prevent these substances becoming too
acidic or too alkaline and damage fabric, skin or hair
Calculations on buffers
o A buffer consists of 0.100moldm-3 Ethanoic Acid and 0. 100moldm-3 Sodium Ethanoate, KA = 1.7 x 10-5, pKA = 4.77.…read more

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Nomenclature and isomerism in organic chemistry
Naming organic compounds
Roots
o -ane means no double bonds
E.g. ethane
o -ene means there is a double bond
E.g. ethane
o -yne means there is a triple bond
E.g.…read more

Page 9

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There are two types
o E-Z isomerism
o Optical isomerism
E-Z isomerism
o Two substituent's may either be on the same side (Z) or on opposite sides (E)
There are no isomers around a single bond as they can rotate around this
There is restricted rotation around a double bond so are not easily converted from one to
another
Optical isomerism
o Occurs when there a four different substituents attached to one carbon atom
This results in two isomers that are mirror images of one…read more

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Synthesis of optically active compounds
A racemic mixture is produced from optically active compounds generating a 50:50 mixture of two optical isomers
o The synthesis of 2-hydroxypropanoic acid (lactic acid)
Stage 1
Stage 2
Optical isomers in the drug industry
o Some drugs are optically active molecules
Many drugs work by a molecule of the active ingredient fitting an area of a cell - called a receptor
Because receptors have a 3D structure, only one of a pair of optical isomers will fit
o Separate…read more

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