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Learning Objective Students will explain how Earth's surface is worn away by chemical weathering.
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What is chemical weathering?
Mr. White Earth Science Learning Objective Students will explain
how Earth's surface is worn away by chemical weathering. Key Terms
oxidation carbonation hydrolysis Kinds of Chemical Weathering
In chemical weathering, substances in water cause substances in
rocks to dissolve. This action weakens the structure of the rocks.
Chemical changes occur when minerals in rocks are broken down into
other substances. They also occur when minerals are added to or
removed from rocks. Chemical weathering is usually caused by
reactions with oxygen, water, or acids. The Statue of Liberty
contains a large amount of copper
The Statue of Liberty contains a large amount of copper. Its thin
copper skin reacts with oxygen in the air to form a green coating.
Oxidation One kind of chemical weathering is oxidation.
Oxidation occurs when oxygen combines with another substance. New
substances called oxides are formed. Rust is an iron oxide. Like
copper statues, rocks can be oxidized. Oxidized rocks change color.
Here, the iron in the rock has reacted with oxygen in the air. The
red streaks are oxidized iron, or rust. Water Most chemical
weathering is caused by water.
Water reacting chemically with a mineral that has little water
content is called hydrolysis. Many minerals in rocks undergo
hydrolysis. For example, feldspar may combine chemically with water
and change to clay. When heated or dried even a little, minerals
formed by hydrolysis may fall apart. Acids Carbon dioxide can
dissolve in rain to form weak carbonic acid.
When this acid comes into contact with certain minerals, a chemical
change called carbonation occurs. The mineral calcite is changed by
this process. Limestone and marble are made of calcite. Buildings
made of these materials are often weathered by carbonation. Many
buildings and building decorations are made of limestone.
Limestone can be damaged by carbonation. Organisms Some green
plants produce weak acids.
Mosses, which grow on rocks, are an example. The acids can wear
away a rock's surface. As acid seeps into cracks in a rock, it can
break the rock apart. Decaying organisms also produce acids, which
contribute to chemical weathering. Checking Concepts What process
will most likely chemically weather an iron-rich rock? What
substances cause most chemical weathering? Answers Oxidation
Oxygen, water and acids The End