Chemistry Unit 5

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  • Created by: stesar
  • Created on: 23-11-17 22:12

Orbitals

Image result for orbitals periodic table

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The Electrochemical Series

(top) Li ... Al ... Cl (bottom)

More reactive (top) - forms from atom to ion easily

Less reactive (bottom) - doesn't form ions easily - tend to stay as atoms

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Electrolysis

Elements/ the ionic substance must be molten or dissolved.

Ionic Equations

Na -> Na+ + e-

E.g. 1) Sodium Chloride

Positively charged ions move to the negative electrode and reduced to make Sodium atoms.

Negatively charged ions move to the positive electrode and are oxidised to make Chlorine atoms.

Electrolysis Solutions

Break up of hydrogen ions and hydroxide ions. H20 -> H+ + OH- = four types of ions present: 2 for ionic compound, 2 for the water.

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Electrolysis

Electrolysis of Sodium Chloride (aq)

NaCl (solution)

Anode - Chloride - swimming pools

Cathode - Hydrogen - margarine 

In solution - sodium hydroxide - soap

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Making Salts

A base is an oxide or hydroxide of a metal e.g. Calcium Oxide (aq) - alkali

If the base is soluted (dissolves in water) then it would be called on alkali e.g. Calcium oxide (aq) - alkali

Making Salts

The chemical reaction between an acid and an alkali/ base is called neutralisation; a salt is formed

Example: hydrochloric acid + Calcium Oxide -> calcium chloride + water

NITRIC ACID - NITRATE
SULPHURIC ACID - SULFATE
HYDROCHLORIC ACID - CHLORIDE 

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Aluminium Oxide - An Amphoteric Substance

If an acid is present, it will act as a base e.g. Aluminium oxide reacts with HOT hydrochloric acid to make aluminium chloride + water (neutralised)

If a hot base is present, it will act as an acid.

Aluminium oxide is a chemically inert (doesn't react) except under certain conditions e.g. when a hot acid or base is present. This means it has a lot of uses:

  • Filler
  • Paint
  • Sunscreen
  • Glass
  • Chromatography

Alkali's

If they dissolve in water, they form metal hydroxide (aq) which are alkalis.

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Definitions

Amphoteric - Substance that can act both as an acid or a base

Alkali - A base that dissolves in water to form hydroxide ions, OH-

Acid - A compound containing hydrogen that dissociates in water to form hydrogen ions

Base - A compound that reacts with an acid to form a salt and water

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Naming Salts

Hydrochloric Acid -> Sodium Hydroxide -> Sodium Chloride

Sulfuric Acid -> Magnesium -> Magnesium Sulfate

Nitric Acid -> Calcium -> Calcium Nitrate

Sulfuric Acid -> Zinc -> Zinc Sulfate

Hydrochloric Acid -> Iron Oxide -> Iron Chloride

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Transition Metals

Transition Metals

  • d block of elements
  • when they react, they lose electrons to form positive ions
  • They lose 4s electrons before they lose 3d electrons
  • They form ions with more than 1 oxidisation state
  • Can form complex ions
  • They form coloured compounds

Ligands

In a solution, transition metals compound from complex ions.

A complex ion consists of a central transition metal ion bonded to ligand

A ligand is a molecule or ion that donates a lone pair of electrons to form a dative covalent bond/ attraction.

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Transition Metals

  • Why transition metals are able to easily form complex ions:
  • Ligand uses a lone pair of electrons
  • Forms a dative-covalent bond
  • Transition metals use their 3d and 4s orbitals to bond so can accept the lone pair of electrons

Uses of Transition Metals

  • Catalyst
  • Platinum + rhodium are used in the catalyst converters
  • Iron is the catalyst in the Haber Process - it lowers the activation energy. This lowers the const and helps the environment.
  • Ammonia is used in fertilisers
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The Contact Process

Vandium (v) oxide is used as a catalyst to make sulfuric acid in the contact process.

  • Stage 1: Sulfur dioxide is made 

The sulphur dioxide is mixed with excess air

  • Stage 2: sulphur trioxide is made
  • Stage 3: Sulfur trioxide is converted into sulfuric acid

Sulfur trioxide is dissolved in concentrated sulfuric acid

The Role of Vandium Oxide

can be used as a catalyst since it can change its oxidisation state

As sulphur dioxide is oxidised to sulphur trioxide, the vandium oxide is reduced

The vandium oxide is then oxidised with oxygen - means it can be used again

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Aluminia and Aluminium Extraction

Aluminia is a form of aluminium oxide found in the mineral bauxite. It is extracted and purified using the Bayer Process. The stages of the process are:

  • Crush the Bauxite
  • React with NaOH (aq) at 170degrees
  • Filter out solid impurities
  • Allow the crystalise to form Al(OH)3
  • Heat in rotary kiln to form Al2O3

Most of the aluminia separated in this way is used in the Hall-Heroult Process to form the aluminium by electrolysis.

Some are used in the refractory material in kilns.There are materials that retain their strength and are chemically stable at high temperatures.

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Aluminium Extraction

Aluminium ore, bauxite is mined and then processed to form alumina, which is aluminium oxide. Molten alumina is then electrolysed using the Hall-Heroult process. 

Cryolite is added to the alumina to lower the melting point and save energy. The lining of the steel tanks is made from carbon, which acts as the negative electrode. Here, aluminium ions are reduced to form molten aluminium

Al3+ + 3e- -> Al

The molten aluminium can then be drained off and cast into ingots. The positive electrodes are made of carbon. Here, oxide ions are oxidised to form oxygen gas.

2O2- -> O2 + 4e-

The carbon electrodes have to be replaced regularly as they react with the oxygen as it forms.

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Titanium Extraction

The main titanium is rutile, which contains titanium dioxide, TiO2. Although titanium has a very similar reactivity to aluminium, it is not generally extracted by electrolysis as the titanium formed often has 'tree-like' crystals, which can affect the electrodes. Also, side-reactions with titanium ions at both electrodes can lead to impurities.

Most titanium is extracted using the Kroll Process

1) Titanium dioxide, coke and chlorine are heated together at about 900degrees, to form titanium chloride

2) Magnesium is used as a reducing agent to form Titanium

The process is expensive due to the large amounts of energy needed to create the very high temperatures involved. Also, the magnesium used in step 2 is produced by an energy-intensive electrolysis process. The process is time-consuming as it's a batch process.

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Functional Groups

Carboxylic Acid  -  COOH  -  ...oic acid

Ester  -  COO  -  ...oate

Aldehyde  -  CHO  -  ...al

Ketone  -  C-CO-C  -  ...one

Alcohol  -  OH  -  hydroxy...  -  ...ol

Alkene  -  C=C  -  ...ene

Alkane  -  C-C  -  ...ane

Haloalkane  -  F, -Cl, -Br, -l  -  Flouro, chloro, bromo, iodo

Alkyl  -  CH3  -  methyl

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Organic Compound

Organic compounds are all carbon-based compounds. There are different families of organic compounds, they are called alkenes, alkanes and alcohols = homologous series

They can be classed as aliphatic (straight or branched chains), alicyclic (Ring Structure) or aromatic (contains a benzene ring)

Alkenes - hydrogen + carbon = hydrocarbon

They are said to be saturated, single bonds only.

Pentane - 5 carbons
Hexane - 6 carbons
Heptane - 7 carbons
Octane - 8 carbons
Nonane - 9 carbons
Decane - 10 carbons

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Alkenes

They are unsaturated, have a double bond. This means they can react with something else.

General Formula - C n H 2 n

Naming organic compounds

The stem is the main part of the name an comes from the longest c-chain

The prefix is the front part of the name and identifies functional groups.

The suffix is the end of the name e.g. 'ene' or 'ane'

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Isomers

Isomer - same atom but different structure

Structural Isomer 

  • Chain isomer
  • Positional isomer - same c chain and functional groups, but the functional groups are on different C's
  • Functional isomer - have different functional groups e.g. C3H6O

Propanone - acetone

Stereoisomer - have the same general formula, but a different arrangement of atoms - different properties, always have a double or triple bond so atoms can rotate. 

Sigma Bonds - 4 electrons in its outer shell, forms 4-C-H covalent bonds. The electron clouds from each bond overlap.

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Definitions

Reaction Mechanisms - step-by-step sequence showing the movement of e's in a process

Halogenation - addition of halogen to an alkane

Homolytic Fission - formation of a free radical by splitting a bond so each free radical has 2 electron

Free Radical - atom with a single unpaired electron

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Propagation and Termination

Propagation - free radicals hit ethane molecule, making longer free radicals. They use ore of the electrons in the double bond to form a new bond between itself and carbon. Other electrons return to the carbon atom. 

Termination - 2 free radicals collide to produce the final molecule (polythene) made up of many different length chains.

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Cracking

Lots of long-chain alkanes = don't need them and want to break them up to make shorter chain alkanes as they're in high demand.

Long-chain molecules are cracked into shorter chains by thermal decomposition (heat)

e.g. octane = hexane +ethane -> make plastics

Alkanes and combustion

Alkanes are often used as fuel as complete combustion releases large amounts of energy.

Complete Combustion - where there's plenty of oxygen

Incomplete Combustion - not enough combustion

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Effects of Temperature on Cracking

Higher the temp = shorter the alkene chain made

High temp = long chain molecules break near ends

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Enthalpy

Is the thermal energy stored in a chemical system

H = U + pV

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Diaphragm V Cell Membrane

The chlorine can react with the sodium hydroxide solution, forming sodium hypochlorite (bleach). To prevent this:

Diaphragm

A membrane with a mixture of asbestos and polymers. Higher level of liquid on anode so NaOH doesn't flow back and mix with chlorine

Cell membrane 

Membrane from a polymer so only positive ions can get through Cl- can't get through to react with NaOH

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Comments

Aamirahmed

Report

Longer carbon chains have stronger london forces as they have more electrons, the elctron density of the larger electron clouds cause them to fluctuate readily creating instanataneous dipoles which are stronger in magnitude there fore more energy is required to break the bonds. This can be applied to a chain such as hexane

Aamirahmed

Report

Therefore the boiling point is higher as it requires more energy

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