Review of Acid/Base and Oxidation/Reduction Conditions

Chemical condtions in the atmosphere, oceans and land surface have a substantial impact on earth materials and processes. Two fundamental characteristics of chemical systems are important for an elementary understanding of earth science.

Before you begin this exercise, make sure you are clear about the definition of an acid and a base, and what determines whether conditions are oxidizing or reducing. See if you can answer the questions below, then check your answers by clicking on the link at the bottom of the page.

1. In introductory earth science courses, we are only concerned with acids and bases in aqueous solution. What are the two ions which determine whether a solution is an acid or a base?

2. For many molecules simply looking at the chemical formula will provide a hint as to whether the molecule is an acid or a base. Determine whether each of the following molecules is an acid or a base:

3. The pH of a solution is a measurement of how acidic or basic it is. If a sample of seawater has a pH of 7.8, is it an acidic or basic solution? If rainwater has a pH of 5.2 and falls into a lake with a pH of 6.5, would you expect the lake to become more acidic or less acidic as more rain falls into it?

4. The presence or absence of oxygen in different environments on the earth's surface has a substantial impact on geological processes. In may cases ancient conditions on the earth will be recorded by the development of soil horizons or depostion of sediment which is then lithified to form sedimentary rock. Some materials will only be preserved under oxidizing conditions, while others require reducing (low oxygen) conditions. For each of the following materials indicate whether preservation will occur under reducing or oxidizing conditions:

5. One convenient property of oxidation/reduction reactions is that they commonly affect the color of the materials which they produce. What can you say about oxidation/reduction by looking at the following images?

The image at right shows some layered sedimentary of Permian age rocks from the Paradox Basin in Colorado. The white layers are gypsum, the others are sandstone. Were these layers deposited under oxidizing or reducing conditions? How can you tell?
	The image at the left shows the surface of a layer of mudstone of Triassic age from southern Queensland, Australia. Were the conditions oxidizing or reducing when this layer was deposited? How can you tell?

Review of Acid-Base (pH) and Oxidation/Reduction Conditions