Chemistry GCSE unit 3 chemistry of elements

Chemistry GCSE unit 3 chemistry of elements 

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  • Created by: jesper
  • Created on: 31-03-12 03:49

Group 1 facts

  • Density increases when you go down the group
  • Melting point decreases as you go up the group
  • Reactivity increases when you go down the group
  • Because they all have one electron in the out most shell they are in group 1
  •  

As you go down the group the outermost electron gets further apart and therefore can easily break free this explains why the alkalis get more reactive as you go down the group.

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The halogen facts

  • Down the group darker in colour
  • Down the group melting point increases 
  • Down the group the boiling point increases
  • Up the group reactivity increases
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Uses of the halogens

Bromine=used to disinfect water because it kills bacteria also used in photography film
+ flame proofing agents, dyes and medicine

Astatines= uses not yet discovered
 

Flourine=the most common use of fluorine, that is a part of everyone's life, is as a common ingredient in toothpastes. Fluoride is used to prevent tooth decay and thus added to toothpastes and mouth washes. 

Chlorine= bleaching and can kill harmful bacteria

Displacement reactions
a more reactive halogen will displace a less reactive halide from compounds in solutions.

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Useful products from the air

  • 78% is nitrogen
  • 21% is oxygen
  • The remaining 1% is mostly argon with carbon dioxide and varying amounts of water
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Cations and Anions

Anions
is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively charged and protons are positively charged).

 Identifying metal ions positive ions (Cations)
·         From solids of the compound
·         Or from the solutions of the compound

Metal ions in solids
the flame test, if a colour is seen in the flame which identifies the metal ion in the compound
Metal ions in solutions
Metal ions are found in ionic compound, so most will dissolve in water to form solution. These solutions can be tested with other substances to identify the aqueous cation.

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Oxygen and oxides.

How can you show that air contains approx one-fifth oxygen?

Using copper.

  • 1.       Set up apparatus with 100cm cubed of air in one of the syrings
  • 2.       Heat the copper at one end of the silica tube using a blue bunsen flame.
  • 3.       Pass the air backwards and forwards over the copper
  • 4.       As the volume in the syrings decreases, move the bunsen flame along  the tube so that it is always heating the fresh copper
  • 5.       Stop heating the syrings when the volume stops decreasing. The copper is reacting with the oxygen in the air to form black copper oxide
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The Laboratory preperation of oxygen

The oxygen can be collected over water. This is because oxygen is not very soluble in water.

Also hydrogen peroxide decomposes slowly to form oxygen and water. This reaction can be sped up by a catalyst sold mangenese dioxide.

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The laboratory preperation of carbon dioxide

The reaction between any metal carbonate and an acid will produce co2. Commonly used is calcuim carbonate. 

Uses of Carbon dioxide:

  •  Making carbonated drinks. Like fizzy drinks, E.g tonic water, coca- cola. Co2 becomes soluble when put under pressure that is why it is so good for fizzy drinks.
  • In fire extinguishers, carbon dioxide does not suport combustion and is more dense than air. So the co2 sits on top of the burning preventing oxygen from reaching it.
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Oxygen is a reactive gas

Element

Observations

Magnesium

Burns with bright, white flame to forma white powder.

Carbon

Burns with a yellow-orange flame to form a colourless gas

Sulfur

Burns a blue flame to form a colourless gas

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Acid rain

Acid rain
Normal rain has the ph of 6 if it gets below this it is acid rain. This can drop because of sulfur dioxides and oxides of nitrogen.

 Problems caused by acid rain:

·         Leaching vital minerals out of the soil and hence causing trees to die

·         Lowering the ph of laes and rivers so that fish and other aquatic life cannot survive

·         Weathering of building and structures made out of limestone, marble and iron 

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