Chemical Weathering

Aim: What factors cause chemical weathering?

Describe what you see and hypothesize how it got this way…

What happened to lady liberty?

1. Chemical weathering

a. Rock is broken down by chemical changes

b. Rock is changed to different minerals and becomes weaker.

When you think chemical weathering, think chemical changes:

Acid,

Dissolving,

Rusting,

Corrosion

2. Causes of chemical weathering:

A. Water

B. Oxygen

C. Carbon dioxide

D. Living organisms

E. Acid rain

A. Water ***Most Important Factor***

Water dissolves minerals in rocks

OR

changes the material into a different mineral

Ex. - Caves

Limestone is dissolved by water. Caves, stalactites and stalagmites can form.

Ex. - Sink Holes

Surface water seeps down and dissolves away the rock.

http://www.youtube.com/watch?v=FqWLa6J--8I

B. Oxidation Iron combines with oxygen when water is

present causing rust Rock gets soft and crumbly and has a red

or brown color

C. Carbonation Carbon dioxide in air mixes with rainwater

forming carbonic acid Acid reacts with marble and limestone

(remember the fizzing mineral!)

D. Living Organisms

Lichens are an organism that will grow on rocks and release an acid that cause chemical weathering.

E. Acid Rain

created when pollution from burning fossil fuels mixes with rain water

Acid rain dissolves rocks over time

Devil’s Marbles

Huge slabs of granite chemically weathered by water in the cracks gives them this rounded appearance.

Lady Liberty

The copper coating on the statue oxidize and turned green

Pennies go through the same chemical change

Which chemical weathering agents may have contributed to Cleopatra’s needle change?

HW Read pgs 42-45Answer question # 4 on pg. 45 and the question below.

4.Why does chemical weathering occur faster in hot wet climates than in cool, dry, climates?

How does rock type affect the rate of weathering?