In the lime soda process once used in large scale munici-pal water softening, calcium hydroxide prepared from lime and sodium carbonate are added to precipitate Ca2+ as CaCO3(s) and Mg2+ as Mg(OH)2(s): Ca2+(aq) + CO32-(aq) → CaCO3(s) Mg2+(aq) + 2 OH-(aq) → MgOH2(aq) How many moles of Ca(OH)2 and Na2CO3 should be added to soften (remove the Ca2+ and Mg2+) 1200 L of water in which [Ca2+] = 5.0x10-4 M and [Mg2+] = 7.0x10-4 M?
Ch.18 - Chemistry of the Environment
Chapter 18, Problem 55
One of the principles of green chemistry is that it is better to use as few steps as possible in making new chemicals. In what ways does following this rule advance the goals of green chemistry? How does this principle relate to energy efficiency?
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Step 1: Understand the principles of green chemistry, which aim to reduce the environmental impact of chemical processes and products by minimizing waste, energy usage, and hazardous substances.
Step 2: Recognize that reducing the number of steps in a chemical synthesis can lead to fewer opportunities for waste generation and the use of hazardous reagents, aligning with the goals of green chemistry.
Step 3: Consider how each step in a chemical process typically requires energy input, such as heating, cooling, or mixing, and how reducing the number of steps can decrease the overall energy consumption of the process.
Step 4: Explore the concept of atom economy, which is related to the efficiency of a chemical reaction in terms of how well the atoms of the starting materials are utilized in the final product, and how fewer steps can improve atom economy.
Step 5: Reflect on how minimizing steps can lead to more streamlined processes, reducing the need for purification and separation, which often require additional energy and resources, thus enhancing energy efficiency.
Related Practice
Textbook Question
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Textbook Question
(a) What are trihalomethanes (THMs)? (b) Draw the Lewis structures of two example THMs.
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Open Question
Suppose that tests of a municipal water system reveal the presence of bromate ion, BrO3-. What are the likely origins of this ion?
Open Question
Discuss how catalysts can make processes more energy efficient.
Textbook Question
A reaction for converting ketones to lactones, called the Baeyer–Villiger reaction,
is used in the manufacture of plastics and pharmaceu- ticals. 3-Chloroperbenzoic acid is shock-sensitive, how- ever, and prone to explode. Also, 3-chlorobenzoic acid is a waste product. An alternative process being developed uses hydrogen peroxide and a catalyst consisting of tin deposited within a solid support. The catalyst is readily recovered from the reaction mixture. (a) What would you expect to be the other product of oxidation of the ketone to lactone by hydrogen peroxide?
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Open Question
In the following three instances, which choice is greener in each situation? Explain (a) Benzene as a solvent or water as a solvent (b) The reaction temperature is 500 K or 1000 K (c) Sodium chloride as a by-product or chloroform (CHCl3) as a by-product.