Effects of Chemical Weathering on Rocks

Type 

Earth Science

Grade Level

Upper Elementary (Grades 5 and 6)

Difficulty of Project

Medium

Cost

The items for this project will cost about $20.00 depending if the rock samples are purchased or collected for free in the field.

Safety Issues

Do not drink the carbonated or tap water used with this science fair project. Carbonated water can cause excess burping and flatulence. There are also disputable claims that it robs the body of calcium.

Material Availability 

Readily available

Approximate Time Required to Complete the Project 

Two days

Objective

Chemical weathering involves the use of chemicals to crack and split rocks into smaller pieces this is done through a combination of water and various chemicals to create an acid which directly breaks down the material. The research aspect of this science fair project is to measure and compare effects of chemical weathering specifically carbonation on several rock samples.

Four jars will be filled with carbonated water and four other jars will contain tape water (control). Several rock samples will be added and allowed to soak in the jars for a set amount of time. The effects on the samples, if any, will be observed and recorded in a data table.  

Materials and Equipment / Ingredients

Package of plastic 8 oz drinking glasses or cups

1-liter bottle of club soda or seltzer water

Masking tape

Clock or watch

2 fragments of each of the following rock samples: limestone, marble, granite, and sandstone

The rocks samples used in this project come in kit form and can be purchased online from Nasco Science retailing for about $13.00. Catalog #SB41176M. Also, the samples may be purchased from a local hobby shop, or depending on where the investigator lives, gathered for free from various field locations such as a rock quarry, road cuts, stream beds, etc. Also a Tri-fold cardboard display board purchased from an art & crafts store. 

Introduction

Weathering is a set of physical, chemical and biological processes that alter the physical and chemical state of rocks and soil at or near the Earth’s surface. Chemical weathering is the process by which rocks are decomposed, dissolved or loosened by chemical processes to form residual materials. Chemical reactions break down the bonds holding the rocks together, causing them to fall apart forming smaller and smaller pieces. Chemical weathering is much more common in locations where there is a lot of water. This is because water is important to many of the chemical reactions that can take place. The most common types of chemical weathering are oxidation, hydrolysis and carbonation. 

This science fair project focuses on the carbonation weathering process by which dissolved carbon dioxide in rainwater or moisture in surrounding air forms carbonic acid which reacts with the minerals (calcium carbonate) in some rocks weakening them and breaking them down into smaller pieces.  

The carbonated water used in this project is simply water that has had pressurized carbon dioxide forced into it. The liquid is usually kept pressurized in its container to prevent the carbon dioxide from escaping the liquid, but once the pressure is gone (i.e. the container is opened) the carbon dioxide escapes causing the liquid to bubble. Carbonated water is used in soft drinks, club soda, and seltzer water.

Digital photos can be taken during the experimenting process and used on the display board:

Research Questions

• What is chemical weathering?
• Which rock samples show that chemical change has occurred?
• For each sample, how did the effect produced by carbonated water compare with the effects produced by water?
• What is the effect of time on the weathering?
• When carbon dioxide dissolves in water it becomes a weak acid called carbonic acid, based on this activity, how does this affect rocks? 

Terms, Concepts and Questions to Start Background Research

Erosion - When particles weathered from rocks are carried away, it is called erosion. Erosion is responsible for wearing down exposed places and depositing sediment in level places. 

Weathering is a set of physical, chemical and biological processes that alter the physical and chemical state of rocks and soil at or near the Earth's surface. 

Chemical weathering occurs as water carrying other chemical elements alters the rocks. An example is carbonic acid. Water combines with carbon dioxide to produce a weak acid (carbonic acid). 

Carbonic acid is a weak acid that consists of dissolved carbon dioxide in water.