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87 Cards in this Set
- Front
- Back
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What does oxidation mean?
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The loss of electrons by a substance
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What does reduction mean?
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The gain of electrons by a substance.
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What does half-reaction mean?
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The processes that describe the transfer of electrons between atoms
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What does redox reaction mean?
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Oxidation-reduction reactions
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What does an oxidizing agent do? Identify some common oxidizing agents.
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An oxidizing agent promotes oxidation. Some common oxidizing agents are H+,Cl2, O2, and O3.
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What does a reducing agent do? Identify some common reducing agents.
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Promotes reduction
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What is an electrochemical cell?
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An apparatus consisting of two electrodes, one positive and one negative, connected by a conducting wire, while being immersed in an ionic solution.
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Define electrode.
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Metal surfaces at which oxidation and reduction reactions occur.
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Define electrolyte.
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Ion-containing solutions into which the electrodes in an electrochemical cell are placed.
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Define salt bridge.
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A device that maintains the anion balance in an electrochemical cell.
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What occurs when an electrochemical cell is discharging?
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During the discharge of an electrochemical cell, the metal surface of one electrode is oxidized to the corresponding ion, which enters the aqueous solution. The electrons from this oxidation travel to the other electrode, where they are transferred to another ion in solution,resulting in the plating of the metal on the electrode. The salt bridge serves to redistribute the anions in order to maintain positive and negative ion balance.
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What is a battery?
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A commercial electrochemical cell, or combination of cells, in which the electrochemical reaction is used to generate electricity.
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What is a fuel cell?
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An electrochemical cell that can be continuously operated and does not become discharged.
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What is electrolysis?
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The technique of passing an electrical current through a material to drive a chemical reaction.
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What is electroplating?
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A technique in which a thin film of metal is deposited on an object.
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What does the term hydrogen economy mean?
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A hypothetical economy in which the energy needed for motive power (for automobiles and other vehicle types) or electricity (for stationary applications) is derived from reacting hydrogen (H2) with oxygen.
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Describe the ways in which hydrogen can be stored.
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A liquid, compressed by gas, as a gas between graphite layers or reversibly absorbed by metals or metal alloys, and as an elemental component of liquid fuel.
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Why does electron transfer occur between two metal strips in a solution even when they are not touching?
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There must be an electrical connection between the two metals, and the two metals must spontaneously undergo an oxidation-reduction reaction.
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What is the role of a salt bridge in an electrochemical cell?
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So that ions can flow between solutions in order to maintain electric neutrality.
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How does a fuel cell differ from a battery?
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Batteries contain a finite, small amount of reactants and eventually become fully discharged and useless. Fuel cells are continuously replenished while the unit delivers electrical power, so it can be continuously operated and never becomes discharged.
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Why is hydrogen gas a desirable choice as a reducing agent in fuel cells?
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Hydrogen can be produced from both fossil fuels and from renewable sources, and it has been the fuel used in most fuel cell technology development efforts.
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How is pure aluminum produced from its ore?
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Electrolysis is used to prepare and purify some metals. Aluminum occurs naturally as its ore. The aluminum in this oxide is present as AL3+, and so it must be reduced to become the free metal. Each aluminum ion must add 3 electrons, since the atoms in a free metal are electrically neutral.
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What role can solar energy play in hydrogen production?
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The electrolysis of water to H2 and O2.
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What are some problems associated with using sunlight to generate hydrogen gas directly from water?
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There is no practical, efficient method. H2O does not directly absorb sunlight. Since the light absorbing substances and other required in the process are not 100% recoverable at the end of the cycle, they must be continuously resupplied, making the whole process uneconomical.
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Where in the atmosphere is air pollution, such as smog, found?
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Troposphere
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Identify the major components of outdoor air pollution.
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Ozone, nitric acid, partially oxidized organic compounds, SO2, and NO.
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Explain what is meant by the term photochemical smog.
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Air pollution caused by chemical reactions requiring sunlight.
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What is a volatile organic compound? Provide an example.
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Carbon-containing substances that readily vaporize into air. EX. Paint, paint-strippers, pesticides.
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How are volatile organic compounds related to smog?
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Volatile organic compounds are the chemical reactants of smog.
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How does a primary pollutant differ from a secondary pollutant? Provide an example of each.
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Primary pollutants are the substances that are initially emitted directly into the air. EX. NO3, hydrocarbons.
Secondary pollutants are substances into which primary pollutants are transformed. EX. O3 and HNO3 |
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How are nitrogen oxide gases formed?
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When fuels are burnt in air.
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Which two sources produce most of the urban NO?
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Vehicles and electric power plants that burn coal, oil, or natural gas.
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To what does the term NOx refer?
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NO and NO2
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What conditions work to create photochemical smog in a city?
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Sunlight, heat, time, + Volatile organic compounds, unburnt gasoline, NO and unburnt hydrocarbons, and NO2
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Describe some of the detrimental effects of ozone.
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Ozone damages plant tissue, hardens rubber, bleaches colors, and is harmful to humans.
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What are anthropogenic hydrocarbons? Provide an example.
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Hydrocarbons that result from human activities. EX. Sulfur Dioxide from electric utility plants burning fossil fuels
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Identify some natural sources of hydrocarbons.
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Deciduous trees and shrubs.
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Explain what a catalytic converter is and describe how it works.
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A catalytic converter is an apparatus in the exhaust system of vehicles which uses a catalyst such as platinum to speed conversion of hydrocarbons, CO3 and NOx, in the exhaust gas into less harmful substances.
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Describe in words how a two-stage combustion process in power plants helps to minimize the amount of NOx that power plants produce and emit.
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First stage uses minimum oxygen; Second stage is carried out at lower temperatures. In both cases, NOx formation is minimized.
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What is acid rain?
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Atmospheric precipitation (rain, fog, snow) with a pH less than 5.
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Is the natural pH of rain water relatively acidic or relatively basic? Explain.
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Due to the presence of dissolved atmospheric carbon dioxide, the natural pH of rainwater is a relatively acidic 5.6.
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What makes acid rain acidic?
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Virtually all of the acidity in acid rain results from sulfuric acid and nitric acid dissolved in the water.
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What natural phenomena produce SO2?
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SO2 is produced by volcanoes and by the oxidation of sulfur gases produced during the decompositions of plants.
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Identify the primary anthropogenic sources of SO2.
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The combustion of coal and nonferrous smelting.
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What is a particulate?
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Tiny solid and liquid particles suspended in air.
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What are the size categories that describe particulates?
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Individual particles are classified as coarse or as fine depending upon whether their diameters are greater or less then 2.5 um.
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How do coarse particles differ from fine particles?
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Diameters greater than 2.5 um are coarse; smaller diameters are fine.
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What is an aerosol?
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A collection of particulates, whether solid or liquid droplets, dispersed in air.
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How does soot differ from mist?
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Soot refers to solid particles in the atmosphere, whereas mist refers to liquid atmospheric particles.
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What are the initial reactants in the formation of photochemical smog?
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VOC's+NO+O2+sunlight
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Explain why ozone is both a pollutant and a necessary component of the atmosphere. What is the difference between ozone that pollutes and ozone that protects?
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Ozone is a necessary protection against dangerous radiation from the Sun when the gas lies high up in the atmosphere. At the same time, ozone is an undesirable constituent of air at low altitudes. The difference is its location in Earth's atmosphere.
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How does a catalytic converter control NOx emissions?
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A catalytic converter uses a catalyst such as platinum to speed conversions of NOx in the exhaust gas into less harmful substances.
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Describe the effects of acid rain on fish populations.
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High concentrations of aluminum are responsible for the devastating decreases in fish populations.
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Describe the effects of acid rain on dissolved aluminum.
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Under normal conditions, when the water has a pH closer to 7, the aluminum is immobilized in the rock by its insolubility. However, this ion is leached from rocks by reactions with the hydrogen ions in acidic water that passes over them.
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Describe the effects of acid rain on trees.
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Acidification of the soil can leach nutrients from it and solubilize aluminum. his element may interfere with the uptake of nutrients by trees and other plants. This along with the ozone at ground levels poses stresses to the trees. The stresses alone will not kill them, but along with drought, temperature extremes, disease, or insect attack make the trees much more vulnerable.
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What is the relationship between the temperature of a catalytic converter and its efficiency?
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A catalytic converter is more efficient when warm.
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What is the ozone layer?
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An area of ozone molecules in the stratosphere that filters out harmful rays from sunlight.
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Where is ozone produced in the atmosphere?
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Tropical regions of the stratosphere.
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What is the ozone hole?
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The decreasing total amount of stratospheric ozone over Antarctica that occurs in the springtime.
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Has ozone depletion occurred only above Antarctica?
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No
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How does visible light differ in wavelength from ultraviolet light?
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Visible light has wavelengths that lie between 400-750nm; Ultraviolet light has wavelengths between about 50-400nm.
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Which range of wavelength is associated with ultraviolet light?
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Wavelengths between about 50-400nm.
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How can UV light affect molecules?
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It may break or alter bond properties.
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How does the absorption spectrum of oxygen,O2, differ from ozone, O3?
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O2 gas that lies above and in the stratosphere filters from sunlight all of the UV light from 120 to 220nm. O2 also filters some of the UV light from 220 to 240 nm. The ultraviolet light in the 220 to 320nm range is filtered from sunlight mainly by the ozone molecule O3.
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Explain how UV-A, UV-B, and UV-C differ.
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UV-C region (200 to 280nm), UV-B region (280 to 320 nm), UV-A region (320 to 400nm).
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Describe some of the biological damage that occurs upon exposure to ultraviolet radiation.
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Most skin cancers in humans are due to overexposure to UV-B in sunlight. There is evidence that increased UV-B levels give rise to an increased incidence of cataracts, particularly among the non-elderly.
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What is malignant melanoma? What is the relationship between malignant melanoma and ultraviolet radiation?
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Malignant melanoma is an often-fatal form of skin cancer believed to be related to short periods of very high UV exposure occurring early in life.
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What negative environmental effects are associated with decreased levels of ozone?
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A decrease in photosynthesis in plants and a negative impact on phytoplankton and small marine life.
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What is a photon?
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The finite packets of matter in which light's energy can be absorbed.
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What is the relationship between the energy of a photon and its wavelength?
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The quantity of energy that is associated with a photon depends on the light's wavelength in an inverse way: the longer the wavelength, the smaller the amount of energy absorbed.
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What is the Chapman Cycle?
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Natural ozone production and noncatalytic destruction processes in the ozone layer.
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What are the catalytically inactive forms of chlorine and bromine in the atmosphere?
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HCl and ClOno2. The chlorine is inactive as a catalyst for ozone destruction.
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What is a vortex?
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A whirling mass of air in which wind speeds can exceed 300km per hour.
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Identify the primary natural and anthropogenic sources of chlorine and bromine in the atmosphere.
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Methyl Chlorine Gas (CH3Cl--naturally forms in the oceans. Much larger amounts of chlorine-containing gaseous compounds are released into the air during their production or use. Bromine is also released in this way.
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What is CFC? What types of chemicals are proposed as long-term CFC replacements?
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CFC's are chlorofluoroucarbons. The chemicals that are proposed as long-term CFC replacements are hydrogen, fluorine, and carbon.
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When light interacts with a CFC-molecule, which chemical bond is broken?
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Carbon-chlorine
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What is a tropospheric sink?
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A process by which the substance is removed.
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CFC's have no tropospheric sink. What are the consequences of this?
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CFC molecules rise through the troposphere and travel into the stratosphere.
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What are the primary sources of CFCs in the atmosphere?
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CFC's are used in refrigeration or as propellants and those used in dry cleaning.
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What is a halon?
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A class of chemicals that are bromine-containing, hydrogen-free substances.
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What is the Montreal Protocol?
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The international agreement where all ozone-depleting chemicals became destined for phaseout in all nations.
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Of UV-A, UV-B, and UV-C, which type penetrates the atmosphere to the greatest extent? Why?
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UV-A because neither ozone nor any other constituent of the clean atmosphere absorbs significantly in the UV-A range.
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Is it possible to destroy all the ozone in the atmosphere permanently?
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No, not as long as UV-C light and free oxygen gas exist.
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What impact does increased UV penetration have on ozone production in lower altitudes?
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Exposure to UV-B causes human skin to sunburn and suntan. Overexposure can lead to skin cancer, the most prevalent form of cancer. Increasing amounts of UV-B may also adversely affect the human immune system and the growth of some plants and animals.
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What role does sunlight play in the formation and disappearance of the Antarctic ozone hole?
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The chemistry of ozone depletion is driven by energy associated with light from the Sun.
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Why does a polar vortex eventually affect ozone levels in other parts of the world? What effect can it have?
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5
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Why does it take so long for chlorine levels to decline in the atmosphere?
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Because of slow vertical motion in the stratosphere.
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