Problem 37 - Chemistry: The Central Science

Question

List the common products formed when an organic material containing the elements carbon, hydrogen, oxygen, sulfur, and nitrogen decomposes (a) under aerobic conditions, (b) under anaerobic conditions.

Step-by-Step Solution

Answer

(a) Under aerobic conditions, the common products are carbon dioxide (CO2), water (H2O), nitrate (NO3-), and sulfate (SO4^2-). (b) Under anaerobic conditions, the common products are methane (CH4), hydrogen sulfide (H2S), ammonia (NH3), and organic acids.

Step 1: Identify the elements present in the organic material

The given organic material contains the elements carbon (C), hydrogen (H), oxygen (O), sulfur (S), and nitrogen (N). We must determine the common products formed when this organic material decomposes under aerobic and anaerobic conditions.

Step 2: List the common products under aerobic conditions

Aerobic decomposition mainly involves the process of aerobic respiration. In this process, microorganisms break down organic materials using oxygen (O2) as the final electron acceptor, producing carbon dioxide (CO2), water (H2O), and energy in the form of adenosine triphosphate (ATP). The other elements (N and S) are often released as inorganic forms such as nitrate (NO3-) and sulfate (SO4^2-), which are typically non-toxic and can be used by organisms as nutrients. The common products under aerobic conditions are: 1. Carbon dioxide (CO2) 2. Water (H2O) 3. Nitrate (NO3-) 4. Sulfate (SO4^2-)

Step 3: List the common products under anaerobic conditions

Anaerobic decomposition occurs in the absence of oxygen. There are various pathways through which anaerobic decomposition can take place, such as fermentation, denitrification, and sulfate reduction. Common products formed under anaerobic conditions include: 1. Methane (CH4) - Produced mainly through a process called methanogenesis, where microorganisms use CO2 as the final electron acceptor and produce methane and water as waste products. Methane is a greenhouse gas and can contribute to climate change. 2. Hydrogen sulfide (H2S) - Produced during sulfate reduction, where microorganisms use sulfate (SO4^2-) as the final electron acceptor, reducing it to hydrogen sulfide (a toxic gas with a rotten egg smell). 3. Ammonia (NH3) - Formed as a result of the breakdown of nitrogen-containing compounds like proteins and amino acids. It can be released into the environment, where it can contribute to eutrophication and harm aquatic organisms. 4. Organic acids (such as lactic acid, propionic acid, and butyric acid) - Produced during fermentation, where microorganisms partially break down organic matter and produce these acids as waste products. These are generally not long-lasting compounds as they are further consumed and transformed by other microorganisms. In summary, the common products formed when an organic material containing the elements carbon, hydrogen, oxygen, sulfur, and nitrogen decomposes: (a) Under aerobic conditions: CO2, H2O, NO3-, and SO4^2- (b) Under anaerobic conditions: CH4, H2S, NH3, and organic acids