Catalysts

A catalyst is a substance that speeds up the rate of a reaction without being used up in it itself.

They do this by lowering the activation energy for a reaction that will increase the likely hood of a particle having enough energy to react so therefore increasing the rate of reaction.

This have large uses in industry especially cars where platinum and rhodium are used to aid the reaction of dangerous gasses of carbon monoxide and nitrogen monoxide into the harmless gasses of carbon dioxide and nitrogen in a catalytic converter.  There are also enzymes that are the same as catalyst's but are living things.  Enzymes are used to make alcoholic beverages by speeding up the break down of glucose into ethanol and carbon dioxide.  They are also used by speeding up the break down of food quickly into smaller parts  

Rocks

There are three types of rocks they are:

1.      Metamorphic

Metamorphic rocks are very crystalline and banded

examples are slate and marble

2.      Sedimentary

Sedimentary rocks are very grainy and crumbly and may contain fossils

examples are sandstone and limestone

3.      Igneous

Igneous rocks are crystalline and very hard

examples are basalt and granite

How they’re formed 

Igneous rocks

These form when molten rock cools down to form crystals.

Sedimentary rocks

These form as layers of sediment built up. Under pressure water is forced out and minerals help the sediment stick together to form rocks.

Metamorphic rocks

These are rocks that have been changed by heat and/or pressure 

WHEN ROCK COOLS QUICKLY WE GET SMALL CRYSTALS

WHEN ROCK COOLS SLOWLY WE GET LARGE CRYSTALS

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 Salt Formation

These are the following methods of preparation:

1.   an acid + metal = metal salt + hydrogen

eg- hydrochloric acid + iron = iron chloride + hydrogen

2.     an acid + a carbonate = metal salt + water + carbon dioxide

eg- sulphuric acid + calcium carbonate = calcium sulphate + water + carbon dioxide

3.     an acid + insoluble base = a salt + water

eg- nitric acid + magnesium oxide = magnesium nitrate + water

4.      an acid + an alkali* = salt + water

eg- hydrochloric acid + sodium hydroxide = sodium chloride + water

*an alkali is a soluble base

5.     Two soluble solutions of salts give an insoluble salt (filter off)

eg- sodium iodide (aq) + lead nitrate (aq) = lead iodide (solid) + sodium nitrate (aq)

6.     Direct combination of elements

eg- aluminum + iodine = aluminum iodide

The Atmosphere

The history of the atmosphere

The volcanoes 4 billion years ago released mainly Carbon Dioxide, a small amount of methane and ammonia.  There was also water vapour, which condensed to form the oceans.

Over 3 billion years ago the first single-celled plants evolved, this meant the Carbon Dioxide levels were reduced and the Oxygen levels increased as plants give out Oxygen.  Carbon Dioxide became locked up in sedimentary rocks and fossil fuels.  Some of the Oxygen combined with ammonia to produce Nitrogen.  More Nitrogen was produced by the action of denitrifying bacteria on Nitrates from decaying plant material.

Then over 1 billion years ago the first multi-celled plant evolved the Oxygen and Nitrogen levels increased to almost present levels:

21% Oxygen and 78% Nitrogen

Free Oxygen increased and the Ozone layer formed.  The Ozone layer filters out harmful U.V. light from the sun; this allowed the evolution of the new land living organisms.

Do you know what percent of carbon dioxide levels are in the atmosphere today?

Acid rain  

Sulphur dioxide and nitrogen oxides are produced when fuels are burned in furnaces and engines.  These gases then react with water vapour in the atmosphere to produce acids.  These acids then fall as acid rain.

The gases themselves can harm plants and animals. Acid rain causes lakes and rivers to become so acidic that plants and animals can not survive. The gases and acid rain causes erosion damage to stone.

The elements of group 7 (The Halogens)

The 5 elements in this group are non-metals

The Halogens are gases, which have coloured vapours are molecules, made up of pairs of atoms

    eg: F₂, Cl₂, I₂

They react with metals to form ionic salts

    eg: Calcium + Chlorine à Calcium Chloride

    Ca _(s)      + Cl_{2 (g)}      à CaCl_{2 (s)}

A halogen atom gains 1 electron to from a 1^- (Halide) ion

The halogen atom has 7 electrons in the outer shell, but the Halide ion has 8 electrons in the outer shell

They become less reactive as you go down the group

They can all form compounds with other non-metallic elements

eg: Chlorine + Hydrogen à Hydrogen Chloride

Cl_{2 (g)}     + H_{2 (g)}          à 2HCl _(aq)

They can all displace less reactive halogens from aqueous solutions of their salts:

Chlorine will displace both Bromine and Iodine (as these are both lower than Chlorine in group 7).

Bromine will displace Iodine but not Chlorine, as Chlorine is higher than Bromine in group 7

eg: Potassium Iodide + Chlorine à Potassium Chloride + Iodine

2KI_(aq)                  + Cl_{2 (g)}      à 2KCl _(aq)                       + I_{2 (aq)}

They have higher melting points as you go down the group

A common use of the halogens is in light sensitive paper (photographic film) eg:

Silver Nitrate + Sodium Chloride à Silver Chloride + Sodium Nitrate

AgNO_{3 (aq)}     + NaCl                     à AgCl _(s)             + NaNO_{3 (aq)}

Silver Halide is used as a coating for photographic paper.  For example, Silver Chloride is reduced to silver by light

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The History of the Periodic Table

Early Attempts to classify the elements

1820s - Johann Dobereiner

In the 1820s Johann Dobereiner a German chemist tried to make sense of the elements known at the time. He noticed if you took three elements with similar properties there was an interesting pattern. The atomic mass of the middle element was nearly halfway between the masses of the other two. However not many elements fell into this pattern. Most people thought 'triads' were just coincidence.

1864 - John Newlands

John Newlands was an English chemist. He thought if you put the elements in order of atomic mass, then every 8^th element was similar. He called this the law of octaves. This only worked for the first 15 known elements. After that his theory broke down. Other scientists suggested putting the elements in alphabetical order.

1869 - Dmitri Mendeleev

Dmitri Mendeleev a Russian chemist finally solved the problem. He put the elements in order of atomic mass like Newland did. Where Mendeleev pattern broke down he would leave gaps for elements not yet discovered. The table he made had similar elements underneath one another. He even changed the order to make sure elements lined up correctly.

This is how the periodic table was formed.

Discovery of Electronic configuration supports the findings of Mendeleev.

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The reactivity series is a list of elements, which are put into that order by measuring how efficiently/violently the element reacts with oxygen, water and dilute acid. Group 1 metals (i.e. sodium and potassium) are very reactive, because the formation of the atoms is in the way that they have only one electron in the outer shell causing them to willingly or sometimes even forcibly react, so they appear at the start of the reactivity series. Elements such as Gold or Platinum however are held together in a very tight bond so that they will not react at all. The reactivity series appears as such (least to most reactive):

Platinum à Gold à Silver à Copper à Hydrogen à Lead à Tin à Iron à Zinc à Carbon à Aluminium à Magnesium à Calcium à Sodium à potassium

It goes from Potassium, which will burn fiercely on water, and explode in acid, to Platinum, which will merely sink in acid.

The reactions which these elements are tested on are:

Metal + Oxygen à Metal oxides

Metal + Water à Metal hydroxide (or oxide) + Hydrogen

Metal + Acid à Metal salt + Hydrogen

(Hydrogen is tested for by filling and sealing a test tube with the suspect gas, and placing a lighted splint at the opening, unseal it and if there is a 'pop' or a 'squeak' then this gas is Hydrogen)

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AS Revision

• Catalytic Converters

• Extraction of Aluminium

• Internal Combustion Engines

• Iron and Steel Extraction and Manufacture

• Extraction of Titanium

Catalytic Converters

Devises used to remove pollutants from the exhaust gasses of a combustion engine such as:

• Carbon monoxide

• Nitrogen Monoxide

• Un-burnt  hydrocarbons

 They contain a honeycomb structure coated in a metal such as platinum, palladium and rhodium. These metals act as a catalyst and remove 90% of pollutants using the following reactions.

2CO + 2NO                           2CO₂ + N₂

C₈H₁₈ + 25NO                     8CO₂ + 12 N₂ + 9H₂O

Exhaust gases in

CO, NO, C₈H₁₈

Catalytic Converter

Gases out

CO_2, N_2, H₂O

Extraction of aluminium

Dissolved in molten cryolite (Na₃AlF₆), aluminium oxide (bauxite, Al₂O₃), usually melting at over 2000^oC, is dissolved, and the melting point is reduced to 970^oC. In a large cell, two carbon electrodes (positive and negative) ensure the following reactions:

Al³⁺ + 3e^-                                                            Al (at the negative electrode [cathode])

2O^2-                                                                      O₂ + 4e^- (at the positive electrode [anode])

At such high temperatures, some of the O₂ molecules react with the carbon anode to form carbon monoxide and carbon dioxide:

2C + O₂                                                             2CO

C + O₂                                                                 CO₂

In the reaction, large amounts of electricity (this is needed to melt the cryolite and decompose the bauxite) are used. The reaction is a continuous one, but of course more bauxite must be added, and the anode must be replaced intermittently as it is converted to carbon dioxide and monoxide. There is also a possible environmental problem with the removal of cryolite with fluoride pollution

Internal combustion engines

        C₈H₁₈ + 8¹/₂ O₂                     8CO + 9H₂O

• Carbon monoxide is formed by the incomplete combustion of petrol in a car engine.

• Oxides of nitrogen are formed when the air/petrol mixture is sparked and explodes.

• A temperature of 2500^oC can be reached when burning petrol vapour.  This provides sufficient activation energy for nitrogen to react with oxygen to form nitrogen monoxide.

N₂ + O₂               2NO

On cooling NO reacts with more oxygen to form NO₂, which with water form Nitric acid, which can lead to acid rain.

2NO + O₂                2NO₂

4NO₂ + 2H₂O + O₂                4HNO₃

Nitrogen dioxide also reacts with oxygen or hydrocarbons in the presence of sunlight to form an irritating photochemical smog.

Iron and steel manufacture

Iron is a very versatile metal that can be used in many ways in industry and construction. The process used to extract the iron from its ore is that of reduction; as iron is normally found combined with oxygen. The process occurs in a blast furnace at temperatures of over 2000 ⁰C, including oxygen, coke, and limestone. This is a continuous process in which iron (III) oxide, coke and limestone are fed into the top of the blast furnace and hot air is blown in through the bottom.

Initially, coke reacts with the hot air in a strongly exothermic reaction:

                 C_(s) + 0_{2 (g)}                        2CO_(g)

This reaction produces the heat needed for the reduction of the iron (111) oxide. The carbon dioxide formed reacts at high temperature with unreacted coke to form carbon monoxide:

                CO_{2 (g)}  + C _(s)                                        2CO_(g)

The carbon monoxide reduces most of the iron (III) oxide at around 1200^oC.

Extraction of metals: Titanium

Properties of Titanium

• low density

• high strength

• high resistance to corrosion

Titanium Ore: Rutile- Titanium (IV) Oxide (TiO₂)

Method of Extraction: Extracted form its chloride by reduction with an active metal

Reaction 1

TiO₂ + 2C + 2Cl₂                     TiCl₄ + 2CO

Conditions

• 900^oC

Titanium (IV) Chloride is a colourless liquid.  It is purified from other chlorides by fractional distillation in an argon atmosphere.

In the UK it is then reduced by sodium in the following exothermic reaction:

Reaction 2

TiCl₄ + 4Na                 Ti + 4NaCl

Conditions

• Initially 550^oC but rising to 1000^oC

• Inert argon atmosphere

The Sodium Chloride by-product is washed out leaving titanium as a granular powder.

This is an expensive process because:

• It is a batch process

• Chlorine and sodium have to be produced first

• High temperatures are involved in both stages of production

• TiCl₄ reacts violently even with water so care must be taken when handling it

• An argon atmosphere has to be maintained to prevent oxidation

•  

Titanium is a metal with very desirable properties and a high abundance but its use is limited by the high cost of production.

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Useful and Interesting Websites

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