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Ch.18 - Chemistry of the Environment
All textbooksBrown 14th EditionCh.18 - Chemistry of the EnvironmentProblem 49
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Chapter 18, Problem 49

The organic anion
Chemical structure of lauryl sulfate, an organic anion in detergents.
is found in most detergents. Assume that the anion under-goes aerobic decomposition in the following manner: C18H29SO3- + 51 O2 → 36 CO2(aq) + 28 H2O (l) + 2 H+(aq) + 2 SO42-(aq) What is the total mass of O2 required to biodegrade 10.0 g of this substance?

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1
Step 1: Write down the balanced chemical equation for the decomposition reaction: C18H29SO3- + 51 O2 → 36 CO2(aq) + 28 H2O (l) + 2 H+(aq) + 2 SO42-(aq).
Step 2: Calculate the molar mass of the organic anion C18H29SO3-. Use the atomic masses: C (12.01 g/mol), H (1.01 g/mol), S (32.07 g/mol), and O (16.00 g/mol).
Step 3: Determine the number of moles of the organic anion in 10.0 g by dividing the mass by the molar mass calculated in Step 2.
Step 4: Use the stoichiometry of the balanced equation to find the moles of O2 required. According to the equation, 1 mole of C18H29SO3- reacts with 51 moles of O2.
Step 5: Calculate the total mass of O2 required by multiplying the moles of O2 (from Step 4) by the molar mass of O2 (32.00 g/mol).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions. It involves using balanced chemical equations to determine the relationships between the quantities of substances involved. In this case, stoichiometry will help calculate the amount of O2 needed to completely react with a given mass of lauryl sulfate based on the provided reaction.
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Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is essential for converting between the mass of a substance and the number of moles, which is necessary for stoichiometric calculations. For lauryl sulfate (C18H29SO3-), knowing its molar mass allows us to determine how many moles correspond to the 10.0 g given in the question.
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Aerobic Decomposition

Aerobic decomposition is the breakdown of organic matter by microorganisms in the presence of oxygen. This process results in the production of carbon dioxide, water, and other byproducts. Understanding this concept is crucial for interpreting the reaction provided, as it highlights the role of O2 in the biodegradation of lauryl sulfate and the overall environmental impact of detergents.
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Textbook Question

The Ogallala aquifer described in the Closer Look box in Section 18.3, provides 82% of the drinking water for the people who live in the region, although more than 75% of the water that is pumped from it is for irrigation. Irrigation withdrawals are approximately 18 billion gallons per day. (b) What process or processes accounts for the presence of arsenic in well water?

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