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2015-07-27

Chemistry : The Earth

Atmosphere

  • The atmosphere is a gaseous layer surrounding the Earth.
  • It mainly consists of two gases, nitrogen and oxygen, and some other gas such as noble gas, carbon dioxide.  

Fractional distillation of air

Purification

    • Filter to remove dust particles 
    • cooled to -80°C to remove water vapor and carbon dioxide.

Liquefaction

    • compressed and cooled rapidly to become -200°C, it is liquefied

Fractional distillation of air

    • liquid air is passed into the fractionating column, then warmed up bit by bit, the gas with a lower boiling point will be collected first.

Uses of Gases

Oxygen

  • Breathing
  • Burning of fuels

Nitrogen

  • Food packaging
  • refrigerant
  • making ammonia

Argon

  • Fill light bulb

Ocean

Sea Water

  • A mixture of salts and water.
  • The common salt found in seawater is sodium chloride.

Solution

  • A solution is a mixture formed when one or more substance dissolved in another substance
  • e.g. sugar dissolved in water, iodine dissolved in alcohol.

Saturated solution

  • A solution which has dissolved the maximum amount of solute at a particular temperature.

Extraction and purification of common salt in sea water

Filtration

Removes insoluble impurities

Evaporation

The product is crude powder.

Crystallization by cooling 

The crystals are small and pure.

Crystallization by evaporation

The crystals are big and pure.

Isolating pure water from sea water

Distillation

  • Note the water flow
  • Anti-bumping granules are used to ensure smooth boiling and prevent the sea water from shooting to the conical flask.

Electrolysis of sea water

  • Electrolysis - decomposing by electricity

Uses of the products 

  • Hydrogen
    • make margarine
    • make ammonia
    • as rocket fuel
  • Chlorine
    • sterilise pools 
    • make polyvinyl chloride
    • make solvents
  • Sodium Hydroxide
    • make soap
    • make drain cleaner
    • naturalize acidic sewage
  • Hydrogen and chlorine
    • Hydrochloric acid
  • Chlorine and Sodium Hydroxide
    • make chlorine bleach

Rocks and minerals

  • Common minerals and ores
    • Calcite - calcium carbonate
    • quartz - silicon dioxide
    • Bauxite - aluminum oxide
    • pyrite - copper iron sulfide
    • haematite - iron(III) oxide
    • galena - lead (II) sulfide

Calcium Carbonate

  • Limestone, chalk, and marble are the common rock with calcium carbonate.
  • Marble is the hardest.

Uses

  • Make Glass
  • Neutralize acidic soil
  • Build status

Chemical Reactions of Calcium Carbonate

Thermal Decomposition

Calcium carbonate decomposes to calcium oxide (quicklime) and carbon dioxide when heated strongly.

Formation of Calcium Hydroxide

Calcium oxide reacts with water to form calcium hydroxide. After filtration, the solution obtained is lime water.

Formation of Calcium Carbonate

Calcium hydroxide (lime water) reacts with carbon dioxide to form calcium carbonate (insoluble in water) and water. If excess carbon dioxide is passed into lime water, calcium hydrogencarbonate (soluble in water) will be formed.

Test for the presence of a chemical

Water

Add the sample to anhydrous copper(II) sulfate, if water is present, the solid turns blue.
OR
Dip the sample to a piece of dry cobalt(II) chloride paper, if water is present, the paper turns blue.

Test for Chloride (Silver Nitrate Test)

  1. Dissolve solid sample in distilled water.
  2. Add acidified silver nitrate solution to the solution, if a white precipitate is formed, the sample contains chlorides.

Why acidified?

To prevent the formation of other precipitates, e.g. silver carbonate, silver sulfite.

Test for carbonates

  1. Add dilute hydrochloric acid to the sample.
  2. Using a delivery tube, pass any gas formed into lime water. If a white precipitate is formed in the lime water, it contains carbonate.

Flame Test

  1. Moisten a clean platinum wire with concentrated hydrochloric acid. This can remove any substance that sticks on the wire.
  2. Dip the wire into the sample (crushed solid or solution)
  3. Heat the wire with a non-luminous flame. Observe the flame color.
Golden yellow for sodium
Lilac for potassium
Brick red for calcium
Green for copper

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