Ch.18 - Chemistry of the Environment

Problem 80

Chapter 18, Problem 80

The water supply for a midwestern city contains the following impurities: coarse sand, finely divided particulates, nitrate ions, trihalomethanes, dissolved phosphorus in the form of phosphates, potentially harmful bacterial strains, dissolved organic substances. Which of the following processes or agents, if any, is effective in removing each of these impurities: coarse sand filtration, activated carbon filtration, aeration, ozonization, precipitation with aluminum hydroxide?

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Identify the type of impurity and match it with the appropriate removal process.

Coarse sand can be removed by coarse sand filtration, which physically separates larger particles from water.

Finely divided particulates can be removed by precipitation with aluminum hydroxide, which helps in coagulating and settling these particles.

Nitrate ions are typically not removed by the processes listed, but biological denitrification or ion exchange methods are effective.

Trihalomethanes can be removed by activated carbon filtration, which adsorbs organic compounds and chlorine by-products.

Dissolved phosphorus in the form of phosphates can be removed by precipitation with aluminum hydroxide, forming insoluble aluminum phosphate.

Potentially harmful bacterial strains can be effectively removed by ozonization, which disinfects water by oxidizing and destroying bacteria.

Dissolved organic substances can be removed by activated carbon filtration, which adsorbs organic molecules from the water.

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Key Concepts

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

Filtration

Filtration is a physical separation process that removes solid particles from liquids or gases by passing the mixture through a filter medium. Coarse sand filtration is effective for removing larger particles, such as sand and debris, while activated carbon filtration targets smaller organic compounds and impurities, including trihalomethanes and dissolved organic substances.

Chemical Precipitation

Chemical precipitation involves adding a chemical agent to a solution to form solid particles that can be removed from the liquid. In this context, aluminum hydroxide can precipitate dissolved phosphates, effectively reducing phosphorus levels in water, which is crucial for preventing eutrophication in aquatic systems.

Ozonization and Aeration

Ozonization is a water treatment process that uses ozone gas to oxidize organic and inorganic contaminants, including bacteria and trihalomethanes, making them easier to remove. Aeration, on the other hand, introduces air into water, promoting the removal of volatile compounds and enhancing the oxidation of dissolved substances, which can help in reducing harmful bacterial strains.

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The estimated average concentration of NO₂ in air in the United States in 2006 was 0.016 ppm. (a) Calculate the partial pressure of the NO₂ in a sample of this air when the atmospheric pressure is 755 torr (99.1 kPa).

Textbook Question

In 1986 an electrical power plant in Taylorsville, Georgia, burned 8,376,726 tons of coal, a national record at that time. (a) Assuming that the coal was 83% carbon and 2.5% sulfur and that combustion was complete, calculate the number of tons of carbon dioxide and sulfur dioxide produced by the plant during the year.

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Textbook Question

In 1986 an electrical power plant in Taylorsville, Georgia, burned 8,376,726 tons of coal, a national record at that time. (b) If 55% of the SO₂ could be removed by reaction with powdered CaO to form CaSO₃, how many tons of CaSO₃ would be produced?

Textbook Question

An impurity in water has an extinction coefficient of 3.45⨉10³ M^-1 cm^-1 at 280 nm, its absorption maximum (A Closer Look, p. 576). Below 50 ppb, the impurity is not a problem for human health. Given that most spectrometers cannot detect absorbances less than 0.0001 with good reliability, is measuring the absorbance of a water sample at 280 nm a good way to detect concentrations of the impurity above the 50-ppb threshold?

Textbook Question

The concentration of H₂O in the stratosphere is about 5 ppm. It undergoes photodissociation according to: H₂O(g) → H(g) + OH(g) (b) Using Table 8.3, calculate the wavelength required to cause this dissociation.

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Textbook Question

The concentration of H₂O in the stratosphere is about 5 ppm. It undergoes photodissociation according to: H₂O(g) → H(g) + OH(g)

OH(g) + O₃(g) → HO₂(g) + O₂(g)

HO₂(g) + O(g) → OH(g) + O₂(g)

What overall reaction results from these two elementary reactions? What is the catalyst in the overall reaction? Explain.