# 7.6: Activity 5 - Reduction and Oxidation Reactions


Name: ______________________________

Section: _____________________________

Student ID#:__________________________

Your instructor has prepared a set out a suite of mesocosms, which have been incubating since the beginning of the semester with some under fully saturated conditions and some under aerobic conditions, representing two different reduction samples.

The objective of this experiment is to evaluate the redox potential (Eh) and the pH of the soil solutions that were incubated with an aerobic or an anaerobic condition during the semester.

You will conduct the following:

1. OLFACTORY OBSERVATIONS…
• Carefully open the lid of the sulfate reduction jar. Do not shake or agitate the suspension.
• Hold the jar in front of your face and use your hand to waft the air towards your nose. Smell the gases being released.
• Record the nature of your observations.
• OBSERVATIONS $$\rightarrow$$
2. SOIL pH MEASUREMENTS…
• Carefully insert the pH electrodes into the suspension in the container.
• Measure the pH of each suspension. It will take about 20 seconds for the pH meter to stabilize each system.
• Record the pH values for each system.
 pH Measurements for $$\rightarrow$$ Control: Organic Matter Addition K2SO4 Addition: OM+K2SO4:

In addition, your instructor has set out another suite of mesocosm experiments with indicator of reduction in soil (IRIS) tubes inserted into the soil for one month. Protocol for interpreting IRIS tubes is also on display for you to review. After interpreting the IRIS tubes please answer the following questions below:

1. Which mesocosms displayed reduction of sulfate?
2. How do you know sulfate was reduced? Please describe in detail below including the chemical reaction involved.
3. What colors indicate reduction of iron? __________________ and ________________.
4. When iron (Fe) is reduced it goes from ____________ to ___________. (form of iron)
5. Reduction of what chemical compound exemplifies the strongest reducing soil conditions? (State the oxidized and reduced forms)
6. Refer to Figure 11 to answer the following questions.
• At the following Redox Potential (Eh) in Mv, and pH ranges, what compounds are being reduced?
• Eh = +400, pH = 8 $$\rightarrow$$ ____________
• Eh = 0, pH = 6 $$\rightarrow$$ ____________
• Eh = -300, pH = 5 $$\rightarrow$$ _____________
• Who is responsible for the microbially mediated reactions at the following ranges?
• Eh = +500, pH = 9 $$\rightarrow$$ ____________________
• Eh = 0, pH = 9 $$\rightarrow$$ _____________________

7.6: Activity 5 - Reduction and Oxidation Reactions is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Anna R. Schwyter & Karen L. Vaughan (UW Open Education Resources (OER)) via source content that was edited to conform to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.