Chemistry - January 2016

Hydrogen - H                   Sodium - Na                   Iron - Fe

Helium - He                     Magnesium - Mg             Silver - Ag                  

Lithium - Li                      Aluminium - Al              Copper - Cu

Beryllium - Be                 Silicon - Si                       Bromine - Br

Boron - B                        Phosphorus - P             Iodine - I

Carbon - C                      Sulphur - S                      Zinc - Zn

Nitrogen - N                    Chlorine - Cl                  

Oxygen - O                     Argon - Ar                      

Fluorine - F                     Potassium - K               

Neon - Ne                       Calcium - Ca                 

The formula of a compound e.g. CO2 means there is one Carbon atom (you never put a 1 after a symbol) and 2 Oxygen atoms (Oxygen atoms always come in pairs) this compound is Carbon Dioxide (a greenhouse gas)

          CO2             +       C           ->        2CO

(Carbon Dioxide)   (Carbon)      (Carbon Monoxide)

The numbers indicate how many atoms there are of a particular element

The letters indicate which elements are used in this compound

Group 1 metals are the most reactive elements to air and water.         Group 1 metals (in order

Sodium reaction with water                                                                                                          of reactivity)

• Forms a sphere after melting                                                                                         -Potassium - K                      
• Fizzes and produces a gas (Hydrogen)                                                                          - Sodium - Na                        
• Dissolves to form a colourless solution                                                                         - Lithium - Li                               
• Moves around                                                                                                                - Calcium - Ca
  

Reaction taking place                                                                                               - Magnesium - Mg

 Sodium + Water -> Hydrogen + Sodium Hydroxide                               - Aluminium - Al

   Na     +     HO ->   2NaOH   +   H2                   Aluminium and magnesium

Test for Hydrogen:                                 

Bring flame in contact with gas - if burns with a high-pitched pop, Hydrogen is present

When Group 1 metals react with oxygen, they lose their original shiny colour, they are quite soft, so can be cut easily, when cut, they reveal their shiny surface, which turns dull after just a few seconds

They must be stored under oil, so that oxygen does not come in cantact with them, and they do not react

Group 2 metals are generally less reactive than Group 1 metals.

When they react with water, oxygen or steam, they produce their oxides (Calcium Oxide etc. and Hydrogen)

Radium + Water -> Radium Oxide + Hydrogen

Acid + Metal --> Salt + Hydrogen

The faster/stronger the reaction, the more reactive the metal is.

We always use acid to react with a reactive metal because the metals are alkali

If the metal is unreactive, you will see no change in the appearance of the metal and acid

e.g.

Magnesium + Hydrocholric Acid --> Magnesium Chloride + Hydrogen

    (Metal)     +      (Acid)               -->            (Salt)                +  (Hydrogen)

Displacement Reaction - A more reactive metal 'displaces' a less reactive metal from one of it's compounds

e.g. Copper Sulphate + Magnesium --> Magnesium Sulphate + Copper (Magnesium takes the sulphate)

We can work out if a displacement reaction will take place by looking at the reactivity of the metals being used for the experiment. If the metal is stronger than the compound, a reaction will take place, otherwise there will be no reaction

Blast Furnaces is used to get the oxygen out of the iron oxide in the ore (e.g. Haematite)

Rust is a chemical reaction that takes place on the surface of a metal - which is a type of corrosion.

An experiment involving 5 nails in identical test tubes proved that both oxygen and water must be present for rust:

Test Tube 1 - Dry Air and Calcium Chloride to absorb water -> No rust

Test Tube 2 - Nail under oil, with boiled water -> No rust

Test Tube 3 - Exposed to water and air -> Rust

Test Tube 4 - Nail + Salt Solution + Air -> Very rusty

Test Tube 5 - Acid Solution + Nail + Air -> Very Rusty

‘Protective Barrier’

·      Paint can prevent water and oxygen getting to the iron. It is also cheap and easily applied

·      Oil and grease are flexible, so are suitable coatings for tools or machinery.

·      Plastic coating, although more expensive, is strong and long lasting. Wire netting is coated with plastic to stop the plastic corroding.

·      Tin plaiting, which is used to make the metal for ‘tin’ cans, are good for food containers, because the coating is strong, non-poisonous and stops corrosion.

·      Electroplating applies a thin layer of protection to expensive metals using electricity, from metals such as chromium and nickel; it forms a tough, shiny coating. This is widely used on taps and cutlery.

‘Sacrificial Protection’

·      This method is used where painting is difficult or impossible

·      It consists of the rusting metal being covered in a reactive metal like Magnesium or Zinc

·      On railway lines, bags of magnesium are attached at regular intervals

·      It works because the reactive metal corrodes, protecting the iron. This give it the name ‘Sacrificial Protection’

·      It is used on oil rigs in the North Sea (Magnesium), the hulls of iron ships (Zinc), underground oil and gas pipes (Magnesium).

‘Galvanising’

·      This method involves the iron or steel, being dipped in molten zinc

·      It is used in girders on bridges

·      Some car body panels

·      Motorway crash barriers

·      Buckets and roofing nails

·   

Galvanising involves a physical barrier and a sacrificial protection

·      The zinc keeps out air and water

·      If the coating becomes scratched, the iron will still be protected because zinc is a more reactive metal

·      Therefore, the zinc also sacrificially protects the iron

Aluminium is a very reactive metal but the oxide layer on its surface proteccts it from reactions. If we clean the oxide from the surface it reacts very well