i

 

 

 

 

Chemical Weathering

 

Chemical weathering - mainly occurs in warm and wet climates.

Water, oxygen and acid can all weather rocks away.  They breakdown rocks by dissolving or reacting with some of the minerals in the rock.

 

Water attack

Water itself can cause chemical reactions with some rocks.  Water attacks one of the minerals in granite, for example.  The granite break down into tiny particles of clay.  These then get washed away.

 

Oxygen attack

Oxygen gas in the air can attack some rocks, particularly those containing iron.  The rusty brown streaks in some rocks are due to iron reacting with oxygen.  This leads to the formation of iron compounds which causes weakness in the rocks, hence the rocks wear away.

 

Acid attack

 

Chemical weathering is not just due to "acid rain" caused by pollution, it is also instigated by ordinary rain.  You probably think that rain-water is pure.  Actually it is slightly acidic.  This is because carbon dioxide gas dissolves in rain as it falls.  The resulting weak acid (carbonic acid) attacks rocks, mainly those containing calcium carbonate.  

Calcium carbonate, in limestone, reacts with carbonic acid:

Calcium carbonate  +  carbonic acid    calcium hydrogencarbonate

CaCo3(s)            +            H2CO3(aq)            Ca(HCO3)2(aq)

Soluble calcium hydrogencarbonate is formed.  So the limestone is slowly worn away.

 

Biological Weathering

 

Tags:Erosion, Weathering, Biological weathering, Acid attack, Water attack, Oxygen attack

 

 

 

© 2012 science-resources.co.uk. All rights reserved | Design by W3layouts