OCE Ch7

7. Long residence times are generally associated with elements that are considered to be nonconservative constituents. a. True b. False

ANSWER: False NOTES: Conservative elements have longer residence times. This is the reason these elements make up the bulk of the ocean's dissolved materials.

15. A higher level of pH is associated with more hydrogen ions. a. True b. False

ANSWER: False NOTES: High levels of pH have less hydrogen ions. More acidic pH levels have more hydrogen ions.

12. An acid is a substance that combines with a hydrogen ion in solution. a. True b. False

ANSWER: False NOTES: An acid is a substance that releases a hydrogen ion in solution. A base is a substance that combines with a hydrogen ion in solution.

2. At saturation, the rate at which molecules of the solute are being dissolved is greater than the rate at which they are precipitating at another location in the solution. a. True b. False

ANSWER: False NOTES: At saturation, the rate at which molecules of the solute are being dissolved equals the rate at which they are precipitating (re-forming into crystals) at another location in the solution.

10. Carbon dioxide is abundant near the ocean surface due to the photosynthesis activities of plants. a. True b. False

ANSWER: False NOTES: Carbon dioxide is quickly used for marine photosynthesis, which causes oxygen to be more abundant near the surface.

3. Pure water has four colligative properties associated with it. a. True b. False

ANSWER: False NOTES: Colligative properties are the properties of solutions. Water alone in not a solution. Seawater, however, is a solution so these properties are associated with it.

5. The salts in the ocean are similar to those of concentrated river water. a. True b. False

ANSWER: False NOTES: If crustal rock is the only source of dissolved minerals to the ocean, then the salts in the ocean should be like those of concentrated river water. But they are not. River water is usually a dilute solution of bicarbonate and calcium ions, while the principal ions in seawater are chloride and sodium. The magnesium content of seawater would also be higher if seawater were simply concentrated river water.

11. Marine animals are unable to break down water molecules to acquire oxygen, but marine plants can produce enough carbon dioxide to support its own metabolism. a. True b. False

ANSWER: False NOTES: No marine animal has the ability to break down water molecules to obtain oxygen directly, and no marine plant can manufacture enough carbon dioxide to support its own metabolism.

8. Sodium and chloride are nonconservative constituents of seawater. a. True b. False

ANSWER: False NOTES: Sodium and chloride are constituents of seawater that occur in constant proportion or change very slowly through time and are conservative constituents. Conservative elements have long residence times.

9. There is a hundred times the amount of gaseous oxygen in the atmosphere than there is dissolved oxygen in the ocean. a. True b. False

ANSWER: True NOTES: About 36% of the gas dissolved in the ocean is oxygen, but there is about a hundred times more gaseous oxygen in Earth's atmosphere than is dissolved in the whole ocean.

13. Rapid amounts of photosynthesis can increase the alkalinity of seawater. a. True b. False

ANSWER: True NOTES: In areas of rapid photosynthesis, pH will rise because plants and plantlike organisms use CO2. Because temperatures are generally warmer at the surface, less CO2 can dissolve in the first place. So surface pH in warm productive water is usually around 8.5.

1. Sodium chloride as a compound does not truly exist in the ocean. a. True b. False

ANSWER: True NOTES: Note that NaCl does not exist as a "salt" in seawater; its components are separated when salt crystals dissolve in water, but they are joined when crystals re-form as water evaporates.

4. Residence times are dependent upon steady-state conditions and a well-mixed ocean. a. True b. False

ANSWER: True NOTES: The concept of a steady state ocean suggests that ions are added to the ocean at the same rate as they are being removed. This theory helps explain why the ocean is not growing saltier. If constituent minerals remain in ocean water longer than the ocean's mixing time, they will become evenly distributed throughout the ocean. The relatively long residence times of seawater's major constituents assure thorough mixing, the foundation of Forchhammer's principle of constant proportions.

14. The pH scale is the logarithmic measure of hydrogen ion concentrations. a. True b. False

ANSWER: True NOTES: The pH scale is logarithmic, which means that a change of one pH unit represents a 10-fold change in the hydrogen ion concentration.

6. Forchhammer was the first to observe that seawater contains fewer silica and calcium ions than river water. a. True b. False

ANSWER: True NOTES: This constant ratio is known as Forchhammer's principle, or the principle of constant proportions. Forchhammer was also the first to observe that seawater contains fewer silica and calcium ions than concentrated river water, and the first to realize that removal of these compounds by marine animals and plants to form shells and other hard parts might account for part of the difference.

19. The average time water stays in the ocean before evaporating is about ____. a. 4,100 years b. 9 days c. 10 years d. 100 years e. 9,100 years

ANSWER: a NOTES: The average time water stays in the ocean (before being evaporated) is about 4,100 years. Once in the air, its residence time is only 9 days.

27. What is the second most abundant ion in seawater? a. sodium b. chloride c. magnesium d. sulfate e. calcium

ANSWER: a NOTES: The most abundance ions in seawater (in order) include chloride, sodium, sulfate, magnesium, calcium, potassium, and bicarbonate.

34. Which essential gas is often in an unusable form in the ocean and atmosphere? a. nitrogen b. oxygen c. carbon dioxide d. methane e. hydrogen

ANSWER: a NOTES: The upper layers of ocean water are usually saturated with nitrogen gas; that is, additional nitrogen gas will not dissolve. Living organisms require nitrogen to build proteins and other important biochemicals, but the vast majority of them cannot use the nitrogen gas in the atmosphere and ocean directly. It must first be bound, or fixed, into usable chemical forms by specialized organisms.

26. What is the source of most of the dissolved materials found in the ocean? a. biological activities b. weathering of crustal rocks c. outgassing d. convection currents e. atmospheric deposition

ANSWER: b NOTES: Although there are multiple sources of the dissolved materials in the ocean, much of the material comes from the weathering of surface rocks from rain and waves. The composition of the ocean is different from rivers because there is the addition of excess volatiles coming from the upper mantle.

37. What factor accounts for the slow return of carbon dioxide to the atmosphere? a. geological uplift b. burial of calcium carbonate shells and skeletons in ocean sediments c. increase of solubility with depth d. photosynthesis by surface organisms e. sediment dissolution

ANSWER: b NOTES: CO2 moves quickly from atmosphere to ocean, but more slowly from ocean to atmosphere. This is because some dissolved CO2 forms carbonate ions, which combine with calcium ions in seawater to form the calcium carbonate, used by many marine organisms to build shells and skeletons. When these organisms die, their coverings and bones sink to form sediments that may, in time, become limestone rock. Most of Earth's surface carbon is stored in sediments. This carbon slowly re-enters the cycle as sediments dissolve and re-form CO2 that can enter the atmosphere.

35. The concentration of ____ increases with depth, and is affected by the calcium carbonate compensation depth. a. ammonia b. carbon dioxide c. hydrogen d. oxygen e. nitrogen

ANSWER: b NOTES: In contrast, plants and plantlike organisms use carbon dioxide during photosynthesis, so surface levels of CO2 are low. Because photosynthesis cannot take place in the dark, CO2 given off by animals and bacteria tends to build up at depths below the sunlit layer. Levels of CO2 also increase with depth because its solubility increases as pressure increases and temperature decreases.

24. Which element would be surprisingly considered a trace element in the ocean despite its abundance in the atmosphere? a. sodium b. nitrogen c. calcium d. chloride e. oxygen

ANSWER: b NOTES: Nitrogen is a trace element in the ocean despite its abundance in the atmosphere. Any element that is less than 1 part per million is considered a trace element.

33. What is a primary source of oxygen to ocean surface water? a. decay of marine organisms b. photosynthesis c. chemosynthesis d. respiration from bacteria e. large quantities of organisms

ANSWER: b NOTES: The sources of the ocean's dissolved oxygen are the photosynthetic activity of plants and plant-like organisms, and the diffusion of oxygen from the atmosphere.

38. Why can seawater hold many times more carbon dioxide than either nitrogen or oxygen at saturation? a. Carbon dioxide is not used in photosynthesis. b. Carbon dioxide is used in mineral formation. c. Carbon dioxide combines chemically with water to form carbonic acid. d. Carbon dioxide is more reactive. e. Carbon dioxide is used by plankton for energy.

ANSWER: c NOTES: Because CO2 combines chemically with water to form a weak acid, water can hold perhaps a thousand times more carbon dioxide than either nitrogen or oxygen at saturation. Carbon dioxide is quickly used for marine photosynthesis, however; dissolved quantities of CO2 are almost always much less than this theoretical maximum. Even so, there is about 60 times as much CO2 dissolved in the ocean as in the atmosphere.

17. _____ is a mixture, not a solution. a. Groundwater b. Air c. Noodle soup d. Coffee with cream e. Seawater

ANSWER: c NOTES: In a mixture, different substances are closely intermingled but retain separate identities. The properties of a mixture are heterogeneous; they may vary from place to place within the mixture. Think of noodle soup as a mixture of noodles and liquid.

16. What is a solute? a. A homogeneously dispersed mixture b. A heterogeneously dispersed mixture c. A substance that dissolves into another substance d. A mixture of two or more substances e. A substance, usually a liquid, which dissolves other substances

ANSWER: c NOTES: In solutions, the solute is usually a dissolved solid or gas. Generally, the concentration of a solute in a solution is less abundant than the solvent.

39. Which substance is considered a nonconservative constituent in seawater? a. bicarbonate b. magnesium c. phosphate d. potassium e. Sulfate

ANSWER: c NOTES: Nonconservative constituents are those substances dissolved in seawater, which are tied to biological or seasonal cycles or to very short geological cycles. They have short residence times. Biologically important nonconservative constituents include dissolved oxygen produced by plants, carbon dioxide produced by animals, silica and calcium compounds needed for plant and animal shells, or the nitrates and phosphates needed for production of protein and other biochemicals.

31. What causes a decrease in oxygen levels beyond the sunlit layer? a. There are fewer animals present b. Mineral precipitation c. The respiration of marine animals and bacteria d. Decreased saturation because of cooler water e. The by-products of photosynthesis

ANSWER: c NOTES: The oxygen concentration decreases below the sunlit layer because of the respiration of marine animals and bacteria, and because of the oxygen consumed by the decay of tiny dead organisms slowly sinking through the area.

45. Which item is not considered to have a basic pH? a. baking soda b. household ammonia c. black coffee d. seawater e. bleach

ANSWER: c NOTES: The pH scale is logarithmic, which means that a change of one pH unit represents a 10-fold change in the hydrogen ion concentration. A modern nonphosphate detergent is a thousand times more alkaline than seawater, and black coffee is a hundred times more acidic than pure water. Pure water, which is neutral (neither acidic nor basic), has a pH of 7; lower numbers indicate greater acidity, and higher numbers indicate greater alkalinity.

25. What is the primary source of sodium ions to the ocean? a. contact with fresh crust b. volcanic vents and outgassing c. weathering of crustal rocks d. percolating seawater through mid-ocean rifts e. dissolution of mineral deposits at hydrothermal vents

ANSWER: c NOTES: The sodium ions come from the weathering of crustal rocks, while the chloride ions come from the mantle by way of volcanic vents and outgassing from mid-ocean rifts.

43. When carbon dioxide first enters the ocean and combines with water, what chemical compound is formed first? a. bicarbonate b. carbonate c. carbonic acid d. calcium carbonate e. hydrogen ions

ANSWER: c NOTES: When CO2 combines with water in ocean carbonic acid is first formed.

41. What is the source of high carbon dioxide levels at middle depths in the ocean? a. mineral formation b. plant photosynthesis c. atmospheric deposition d. decay of the remains of organisms e. venting and outgassing

ANSWER: d NOTES: At middle depths and in deep water, more CO2 may be present than at the surface. Its source is the respiration of animals and the decay of the remains of organisms falling from the sunlit layer above (bacterial respiration).

28. What is the approximate mixing time of the ocean? a. 16,000 years b. 160 years c. 16 years d. 1,600 years e. 1.6 million years

ANSWER: d NOTES: Because of the vigorous activity of currents, the mixing time of the ocean is thought to be on the order of 1,600 years, so the ocean has been mixed hundreds of thousands of times during its long history.

40. The ocean is becoming more acidic as it absorbs additional ____ from the atmosphere. a. nitrogen b. ozone c. ammonia d. carbon dioxide e. Oxygen

ANSWER: d NOTES: Burning fossil fuels to provide energy for transportation and industry produces a large amount of carbon dioxide. The ocean serves as a natural sink for this excess carbon dioxide—the ocean took up about 25% of the CO2 emitted by human activity in the period 2000 to 2006. The CO2 combines with water to become carbonic acid. The additional carbonic acid produced has made the ocean less alkaline.

23. What is the colligative property that deals with the freezing point of water? a. Sea ice forms at a higher temperature than freshwater ice. b. Salinity disrupts the hydrogen bonding in water and increases the freezing point. c. Salt crystals become incorporated into ice as it forms causing the temperature to increase. d. Salinity disrupts the hydrogen bonding in water and acts as a type of antifreeze. e. Lake ice forms at a lower temperature than sea ice.

ANSWER: d NOTES: Dissolved salts disrupt the webwork of hydrogen bonding in water. As salinity increases, the freezing point of water becomes lower; the salts act as a sort of antifreeze. Sea ice therefore forms at a lower temperature than ice in freshwater lakes.

36. Forchhammer's principle explains ____. a. seawater pH b. seawater buffering capacity c. the carbonate cycle d. conservative seawater constituents e. the salinity gradient in the water column

ANSWER: d NOTES: In 1865, the chemist Georg Forchhammer noted that although the total amount of dissolved solids (salinity) might vary among samples, the ratio of major salts was constant in samples of seawater from many locations. In other words, the percentage of various salts in seawater is the same in samples from many places, regardless of how salty the water is. This constant ratio is known as the principle of constant proportions and identifies the conservative and nonconservative constituents of seawater.

21. What is a correct modification of a physical property of water by changing its salinity? a. Freezing point increases with salinity. b. Boiling point decreases with salinity. c. Seawater evaporates faster than freshwater. d. Osmotic pressure rises with increasing salinity. e. Heat capacity increases with increasing salinity.

ANSWER: d NOTES: Osmotic pressure, the pressure exerted on a biological membrane when the salinity of the environment is different from that within the cells, rises with increasing salinity.

22. Which term describes the average length of time an atom of an element spends in the ocean? a. longevity b. durability time c. saturation time d. residence time e. steady state

ANSWER: d NOTES: Residence time explains why the ocean does not become progressively saltier with age. The residence time of an element can be calculated by dividing the amount of an element in the ocean by the rate at which the element is added or removed from the ocean.

29. How does a salinometer measure salinity? a. It calculates the salinity by measuring the chlorinity. b. It measures the refractive index of seawater. c. It calculates the salinity based on the density of the seawater. d. It measures the conductivity of seawater. e. It measures the number of salt molecules in a given mass of seawater.

ANSWER: d NOTES: The conductivity of seawater varies with salt concentrations and temperatures. Salinometers are able to adjust for the water temperature and be calibrated against samples of known conductivity and salinity.

44. What is the average pH of the ocean? a. 7.0 b. 7.5 c. 6.5 d. 8.5 e. 8.0

ANSWER: e NOTES: Although the pH can vary in particular regions and depths of the ocean, the average pH is 8.0. The amount of carbon dioxide can have large impacts on the pH levels. The range of pH found in the ocean is approximately 7.0 to 8.5.

18. Why does oil not dissolve in water? a. It forms a solution with water b. It has ionic bonds. c. It is found within tissues of organisms. d. It is a polar molecule. e. It forms a mixture with water.

ANSWER: e NOTES: Oil doesn't dissolve in water even if the two are thoroughly shaken together. When oil is dispersed in water, it forms a mixture because molecules of oil are nonpolar in character. This means that oil has no positive or negative charges to attract the polar water molecule.

30. What is the term for ocean components not accounted for by the weathering of continents? a. trace elements b. colligative properties c. conservative constituents d. nonconservative constituents e. excess volatiles

ANSWER: e NOTES: The components of ocean water whose proportions are not accounted for by the weathering of surface rocks are called excess volatiles.

42. What happens to pH levels in regions where there is excess carbon dioxide present? a. Carbon dioxide does not heavily impact pH levels. b. The seawater is able to buffer enough that there is no change. c. The pH levels increase in these regions. d. The seawater becomes more alkaline. e. The pH levels decrease in these regions.

ANSWER: e NOTES: The pH level in the ocean can be altered in the ocean with changes in carbon dioxide. Higher levels of carbon dioxide, which often occurs at, middle depths in the ocean causes the water to be less alkaline.

32. What type of water mass dissolves a higher concentration of gases? a. temperate water masses b. subtropical water masses c. tropical water masses d. equatorial water masses e. polar water masses

ANSWER: e NOTES: Unlike solids, gases dissolve most readily in cold water. A cubic meter of chilly polar water usually contains a greater volume of dissolved gases than a cubic meter of warm tropical water.

20. What is the main avenue that water takes while moving from ocean to air? a. movement with glaciers b. runoff from land c. movement through ground d. precipitation e. evaporation from the ocean

ANSWER: e NOTES: Water cycles continuously. The hydrologic cycle is powered by solar radiation. About 85% of all water entering the atmosphere evaporates from the ocean (the remaining 15% comes from water on land).