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- The atmosphere of Mars is 96% CO2, with a pressure of approximately 6 * 10⁻³ atm at the surface. Based on measurements taken over a period of several years by the Rover Environmental Monitoring Station (REMS), the average daytime temperature at the REMS location on Mars is –5.7 °C (22 °F), while the average nighttime temperature is –79 °C (–109 °F). This daily variation in temperature is much larger than what we experience on Earth. What factor plays the largest role in this wide temperature variation, the composition or the density of the atmosphere?
Problem 36
Problem 37
What is the molarity of Na+ in a solution of NaCl whose salinity is 5.6 if the solution has a density of 1.03 g>mL?
Problem 38
Phosphorus is present in seawater to the extent of 0.07 ppm by mass. Assuming that the phosphorus is present as dihydrogenphosphate, H2PO4-, calculate the correspond-ing molar concentration of H2PO4- in seawater.
Problem 39a
The enthalpy of evaporation of water is 40.67 kJ/mol. Sunlight striking Earth's surface supplies 168 W per square meter (1 W = 1 watt = 1 J/s). (a) Assuming that evaporation of water is due only to energy input from the Sun, calculate how many grams of water could be evaporated from a 1.00 square meter patch of ocean over a 12-h day
Problem 39b
The enthalpy of evaporation of water is 40.67 kJ/mol. Sunlight striking Earth's surface supplies 168 W per square meter (1 W = 1 watt = 1 J/s). (b) The specific heat capacity of liquid water is 4.184 J/g°C. If the initial surface temperature of a 1.00 square meter patch of ocean is 26 °C, what is its final temperature after being in sunlight for 12 h, assuming no phase changes and assuming that sunlight penetrates uniformly to depth of 10.0 cm?
Problem 40b
The enthalpy of fusion of water is 6.01 kJ/mol. Sunlight striking Earth's surface supplies 168 W per square meter (1 W = 1 watt = 1 J/s). (b) The specific heat capacity of ice is 2.032 J/g°C. If the initial temperature of a 1.00 square emter patch of ice is -5.0°C, what is its final temperature after being in sunlight for 12 h, assuming no phase changes and assuming that sunlight penetration uniformly to a depth of 1.00 cm?
- At the first-stage recovery of magnesium from seawater, the precipitation of Mg(OH)2 with CaO occurs in the following reaction: Mg2+(aq) + CaO(s) + H2O(l) → Mg(OH)2(s) + Ca2+(aq). What mass of CaO, in grams, is needed to precipitate 1000 lb of Mg(OH)2?
Problem 41
- Gold is found in seawater at very low levels, about 0.05 ppb by mass. Assuming that gold is worth about $1300 per troy ounce, how many liters of seawater would you have to process to obtain $1,000,000 worth of gold? Assume the density of water is 1.03 g/mL and that your gold recovery process is 50% efficient.
Problem 42
Problem 44a
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. (a) Assuming that 2% of the rainfall that falls on an area of 600,000 km2 recharges the aquifer, what average annual rainfall would be required to replace the water removed for irrigation?
Problem 44b
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?
- Assume that a portable reverse-osmosis apparatus operates on seawater, whose concentrations of constituent ions are listed in Table 18.5, and that the desalinated water output has an effective molarity of about 0.02 M. What minimum pressure must be applied by hand pumping at 297 K to cause reverse osmosis to occur? (Hint: Refer to Section 13.5.)
Problem 46
- 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.
Problem 47
Problem 49
The organic anion
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?
Problem 51
Magnesium ions are removed in water treatment by the addition of slaked lime, Ca(OH)2. Write a balanced chemical equation to describe what occurs in this process
Problem 52
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?
Problem 53
(a) What are trihalomethanes (THMs)? (b) Draw the Lewis structures of two example THMs.
- Suppose that tests of a municipal water system reveal the presence of bromate ion, BrO3-. What are the likely origins of this ion?
Problem 54
- 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?
Problem 55
- Discuss how catalysts can make processes more energy efficient.
Problem 56
Problem 57a
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?
- 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.
Problem 59
Problem 60
In the following three instances, which choice is greener in a chemical process? Explain. (a) A reaction that can be run at 350 K for 12 h without a catalyst or one that can be run at 300 K for 1 h with a reusable catalyst.
- A friend of yours has seen each of the following items in newspaper articles and would like an explanation: (a) acid rain, (b) greenhouse gas, (c) photochemical smog, (d) ozone depletion. Give a brief explanation of each term and identify one or two of the chemicals associated with each.
Problem 61
Problem 62
Suppose that on another planet the atmosphere consists of 17% Kr, 38% CH4, and 45% O2. What is the average molar mass at the surface? What is the average molar mass at an altitude at which all the O2 is photodissociated?
- If an average O₃ molecule “lives” only 100–200 seconds in the stratosphere before undergoing dissociation, how can O₃ offer any protection from ultraviolet radiation?
Problem 63
Problem 64
Show how Equations 18.7 and 18.9 can be added to give Equation 18.10.
- What properties of CFCs make them ideal for various commercial applications but also make them a long-term problem in the stratosphere?
Problem 65
- Halons are fluorocarbons that contain bromine, such as CBrF3. They are used extensively as foaming agents for fighting fires. Like CFCs, halons are very unreactive and ultimately can diffuse into the stratosphere. (b) Propose a mechanism by which the presence of halons in the stratosphere could lead to the depletion of stratospheric ozone.
Problem 66
Problem 67
(a) What is the difference between a CFC and an HFC?
- Explain, using Le Châtelier’s principle, why the equilibrium constant for the formation of NO from N2 and O2 increases with increasing temperature, whereas the equilibrium constant for the formation of NO2 from NO and O2 decreases with increasing temperature.
Problem 68