ACTIVITY 1: Weathering - breaking
up, or breaking down material at the Earth’s surface
Purpose:
To consider different types of weathering process.
Notes:
The apparatus and materials required are: granite chips, 7-10mm
across; Bunsen burner, mat, safety goggles and matches; 500ml
beaker of water; 2 small chips of several different types of
rock, some porous; some non-porous; two shallow plastic containers;
deep freeze or freezing compartment of fridge; boiling tube;
deionised water; Universal indicator; drinking straw or glass
tube; ground limestone (for extension: 4 boiling tubes; 3 bungs
for tubes; limestone fragment; granite fragment; pulverised granite.
Development of knowledge and understanding:
Weathering is investigated by these activities. Weathering loosens
solid material and removes dissolved material. It is distinct
from erosion –
in which solid material is removed.
Demonstration 1A: Weathering - A Physical Example
Learning objective:
To demonstrate how cycles of heating and cooling can cause a granite
chip to break up.
Carry out a risk assessment. Safety
goggles should be worn by all those within range.
Heat a granite chip strongly in the Bunsen flame and then dunk
it into a beaker of cold water (do not drop it to the bottom of
the beaker or the glass may crack). Repeat the process until it
crumbles
- How many cycles were needed?
- How does this represent the ‘real world’?
- Where on Earth might activity like this take place?
- In what ways is it unrealistic?
- Why might you expect a rock containing several minerals to
break down by heating and cooling more quickly than one made
of only one mineral?
Demonstration 1B: Weathering - A Physical Example
Learning objective:
To investigate which rocks are broken down by cycles of freezing
and thawing.
- Use two shallow plastic containers
- Get two chips of several different types of rocks and put
one of each rock into each container. Cover each set of rocks
with water and put one into a deep freeze.
- When frozen, remove the container from the deep freeze and
allow the ice to melt.
- Compare the two containers.
- Replace the one that was frozen before in the deep freeze
and freeze it again, then repeat.
- How do the results compare?
- Which types of rock broke down most quickly?
- Can you explain why?
- How does this represent the ‘real world’?
- Where on Earth might activity like this take place?
- In what ways is it unrealistic?
- Why was a plastic container used and not a glass one?
Demonstration 1C: Weathering - A Chemical Example
Learning objective:
To use indicator to investigate the reaction between carbonic acid
and limestone.
- Add some Universal indicator to deionised water in a boiling
tube (half full).
- Make some “carbonic acid” by blowing exhaled air
through a straw into the water. Record the colour of the indicator.
- Add a spatula full of ground limestone to the boiling tube,
put in the bung and shake well.
- Observe the tube at intervals and look for any change in the
colour of the indicator.
- What has happened?
- Can you explain why?
- How does this represent the ‘real world’?
- Where on Earth might activity like this take place?
- In what ways is it unrealistic?
- Why might some rocks be attacked at a faster rate in industrial
areas?
Extension 1:
Set up a similar activity, using a solid limestone fragment in
another boiling tube, and compare the rate of reaction.
Extension 2:
Set up three boiling tubes, with neutral, deionised water and indicator.
Add a small granite chip to one: add the same amount of pulverised
granite to the second, and keep the third as a control. Seal each
tube tightly with a bung.
After several days, the indicator in the pulverised granite tube
shows an increase in pH. This is because of hydrolysis of the feldspar
mineral in the granite. It is altering to a clay mineral, and releasing
KOH.
Weathering: Two Examples of Biological Weathering - Display/Collect
Your Own
- The oyster shell has been bored (!) by marine organisms, and
will not survive much longer in one piece.
- Mosses and lichens usually represent the first stages of biological
weathering of rocks on the Earth’s surface. (The growth
of tree roots along bedding planes and joints also exert powerful
forces, which break up rocks.)
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