Air & Water

Air is a mixture of gases with different boiling points. Approximately 78% Nitrogen and 21% Oxygen. With small amounts of water vapour, carbon dioxide, neon and argon. 

Dry air, free from co2 can be liquefied and then fractionally distilled to obtain oxygen and nitrogen. 

Elements can burn in air to form oxides, which can be classified as acidic, basic and amphoteric. 

Water soluble oxides of metals give alkaline solutions

Water soluble oxides of non-metals give acidic solutions

OXIDATION and REDUCTION involve the addition and removal of oxygen respectively.

Air is often polluted by carbon monoxide, sulfur dioxide and oxides of nitrogen. 

Carbon monoxide is toxic. Sulfur dioxide causes acid rain. Oxides of nitrogen cause smog. 

Question! What is the test for oxygen? 

Natural waters contain dissolved salts, which can be removed to obtain pure water. 

Pure water can be formed through distillation. It involves evaporation followed by condensation.

This process is called desalination and removes salt from seawater. This makes undrinkable water palatable., but is only economic in situations where these is an acute shortage of water.

Drinking water should have sufficiently low levels of dissolved salts and microbes.

Question! What does chlorine do to drinking water?  

The chemical name for rust is....  hydrated iron oxide. 

For rusting to occur, water and air need to be present. 

Rusting refers to the corrosion of iron. Make sure you know experiments that show both air and water need to be present. 

Ways rusting can be prevented:-

Painting, Greasing, Tin plating, Chromium plating, Galvanising. Learn these. 

Paint is non-permeable and does not allow the metal to react with moisture in the air. Galvanizing is useful in the automotive industry. 

Sacrificial protection is when a metal rusts itself in place of another metal.

For example: Zinc and magnesium prevent iron from rusting but copper makes it worse.

More reactive metals prevent the iron from rusting by reacting itself.