Mid Terms Study Guide- Questions from the Book

17. . For the following molecules, list the number and type (metal, nonmetal, or metalloid) of atoms that each contain. a. CO2 b. H2S c. NO2 d. SiO2

a. 1 carbon atom, 2 oxygen atoms b. 2 hydrogen atoms, 1 sulfur atom c. 1 nitrogen atom, 2 oxygen atoms d. 1 silicon atom, 2 oxygen atoms

13. Balance the following equations in which ethane, C2H6, burns in oxygen. a. C2H6(g) + O2(g) ⟶ C(s) + H2O(g) b. C2H6(g) + O2(g) ⟶ CO(g) + H2O(g) c. C2H6(g) + O2(g) ⟶ CO2(g) + H2O(g) d. Explain why the coefficients for oxygen vary, depending on whether C, CO, or CO2 is formed.

a. 2 C2H6(g) + 3 O2(g) ⟶ 4 C(s) + 6 H2O(g) b. 2 C2H6(g) + 5 O2(g) ⟶ 4 CO(g) + 6 H2O(g) c. 2 C2H6(g) + 7 O2(g) ⟶ 4 CO2(g) + 6 H2O(g) d. The balanced equations show that complete combustion requires the highest ratio of oxygen to ethane (7:2). If a 5:2 ratio is present, carbon monoxide is formed instead of carbon dioxide. If only a 3:2 ratio is available, then carbon (soot and particulate matter) is formed. Note: With less oxygen, the products are likely to be mixed, rather than pure CO or pure soot.

13. a. Draw the Lewis structure for methanol (wood alcohol), H3COH. b. Based on this structure, predict the H─C─H bond angle. Explain your reasoning. c. Based on this structure, predict the H─O─C bond angle. Explain your reasoning

a. 3(1) + 4 + 6 + 1 = 14 outer electrons. This is the Lewis structure: b. The geometry around the C atom is tetrahedral, and there are no lone pairs. A H-C-H bond angle of about 109.5° is predicted. c. There are four pairs of electrons around the O atom, two of which are bonding pairs, while the other two are nonbonded pairs. Repulsion between the two nonbonded electron pairs and their repulsion of the bonding pairs is predicted to cause the H-O-C bond angle to be slightly less than 109.5°, about 104.5°.

6. Express 1.00 m in terms of cm, µm, and nm. Use proper scientific notation in your answers.

1 × 102 cm, 1 × 106 μm, 1 × 109 nm.

18. Name the following nitrogen-containing compounds: NO2, N2O, NO, NCl3, and N2O4.

NO2 = nitrogen dioxide N2O = dinitrogen monoxide NO = nitrogen monoxide NCl = nitrogen trichloride N2O4 = dinitrogen tetroxide

23. raw Lewis structures for any two different CFCs.

Answers will vary. To qualify as CFCs, the compounds should contain only carbon, chlorine, and fluorine. Possibilities include

8. Consider the following blank periodic table, which excludes the lanthanide and actinide elements. a. Locate the region of the periodic table in which metals are found. b. Common metals include iron, magnesium, aluminum, sodium, potassium, and silver. Give the chemical symbol for each. c. Locate the region of the periodic table in which nonmetals are found. d. Give the name and chemical symbol for five nonmetals (elements that are not in your shaded region).

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14. Provide the number of protons, neutrons, and electrons for an atom copper with a mass number of 64.

29 protons, 29 electrons, 35 neutrons

10. Give the name and symbol for an element with this number of valence electrons. a. 2 b. 8 c. 6

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19. The microwaves in home microwave ovens have a frequency of 2.45 × 109 s−1. Is this radiation more or less energetic than radio waves? Than X-rays?

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27. The following free radicals all play a role in catalyzing ozone depletion reactions: Cl•, •NO2, ClO•, and •OH. a. Count the number of outer electrons available and then draw a Lewis structure for each free radical. b. What characteristic is shared by these species that makes them so reactive?

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23. a. Calculate the average mass in grams of an individual atom of silver. b. Calculate the mass in grams of 10 trillion silver atoms. c. Calculate the mass in grams of 5.00 × 10^45 silver atoms.

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29. Give the symbol showing the atomic number and the mass number for the isotope that has: a. 9 protons and 10 neutrons (used in nuclear medicine). b. 26 protons and 30 neutrons (the most stable isotope of this element). c. 86 protons and 136 neutrons (the radioactive gas found in some homes).

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4. a. The concentration of argon in air is approximately 0.934%. Express this value in ppm. b. The air exhaled from the lungs of a smoker has a concentration of 20-50 ppm CO. In contrast, air exhaled by nonsmokers is 0-2 ppm CO. Express each concentration as a percent. c. On a very humid day, the water vapor concentration in the air might be 8500 ppm. Express this as a percent. d. A sample of air taken from Antarctica was found to contain 8 ppm water vapor. Express this as a percent.

Be careful not to confuse the absolute humidity calculated in this problem with relative humidity, which is the amount of water vapor in the air compared to the maximum possible amount of water vapor that the air can hold at a particular temperature. For example, in a rainforest, the relative humidity is usually between 75 and 95%. d. 8 ppm is 0.0008% (move the decimal 4 places to the left).

11. Draw the Lewis structure and name the molecular geometry for each molecule. a. H2S b. OCl2 (oxygen is the central atom) c. N2O (nitrogen is the central atom)

Chapter 4 #11

3. Convert the diameter of the period at the end of this sentence into nanometers

Exact answer will vary depending on viewing size of text. An approximate measurement for the period could be 0.25 mm. Converting this to nanometers:

16. If a carbon dioxide molecule interacts with certain photons in the IR region, the vibrational motions of the atoms are increased. For CO2, the major wavelengths of absorption occur at 4.26 micrometers (μm) and 15.00 micrometers (μm). a. What is the energy corresponding to each of these IR photons? b. What happens to the energy in the vibrating CO2 species?

If the vibrating molecule CO2 collides with another molecule, such as N2 or O2, the energy can be transferred to the second molecule. The energy can also be spontaneously emitted back to the atmosphere or into space

25. According to Table 2.1 the percentage of carbon dioxide in inhaled air is lower than it is in exhaled air. How can you account for this relationship?

In respiration, inhaled oxygen reacts with substances in your body to produce carbon dioxide and water vapor. Therefore, exhaled air has a decreased percentage of oxygen and an increased percentage of carbon dioxide.

8. If you had a sample of 500 particles of air, how many of these particles would be nitrogen, oxygen, and argon?

Nitrogen is 78.0% of the air, meaning that out of 100 air particles, 78 of them are nitrogen molecules. 390 Nitrogen Molecules Oxygen is 21.0% of the air, meaning that out of 100 air particles, 21 of them are oxygen molecules. 105 Oxygen Molecules Argon is 0.9% of the air, meaning that out of 100 air particles, 0.9 of them are argon atoms. =4.5 argon atoms (or between 4 and 5 argon atoms)

16. Arrange the wavelengths in question 14 in order of increasing energy. Which wavelength possesses the most energetic photons?

Note: c = 3.0 × 108 m/s and E = hv, in which h = 6.63 × 10−34 J·s. a. E = (6.63 × 10−34 J·s)(1.5 × 1010 s−1) = 1.0 × 10−24 J b. E = (6.63 × 10−34 J·s)(8 × 1014 s−1) = 5 × 10−19 J c. E = (6.63 × 10−34 J·s)(6 × 1012 s−1) = 4 × 10−21 J d. E = (6.63 × 10−34 J·s)(2.0 × 109 s−1) = 1.3 × 10−24 J The most energetic photons correspond to the shortest wavelength, 400 nm.

54. Although oxygen exists as O2 and O3, nitrogen exists only as N2. Propose an explanation for these facts.

O2, O3, and N2 all have an even number of valence electrons. In contrast, N3 would have 15 valence electrons. Molecules with odd numbers of electrons cannot follow the octet rule, making them free radicals and more reactive.

1. How does ozone differ from oxygen in its chemical formula? In its properties?

The chemical formulas of ozone and oxygen are O3 and O2, respectively. Both are gases, but they differ in their properties. Oxygen has no odor; ozone has a very sharp odor. Although both are reactive, ozone is much more highly so. Oxygen is necessary for many forms of life; in contrast, ozone is a harmful air pollutant in the troposphere. However, ozone in the stratosphere helps to protect us from the harmful ultraviolet rays of the sun

30. The EPA has used the slogan "Ozone: Good Up High, Bad Nearby" in some of its publications for the general public. Explain the message.

The message is that ground-level ozone is a harmful air pollutant. Ozone in the stratosphere, on the other hand, is beneficial because it can absorb harmful UV-B before it reaches the surface of Earth.

The surface temperatures of both Venus and Earth are warmer than would be expected on the basis of their respective distances from the Sun. Why is this so?

These two planets are warmer than would be expected because they have atmospheric gases that produce a "greenhouse effect." Sunlight enters the atmosphere of both Earth and Venus, warming the surfaces of the planet. The atmospheric gases are able to trap some of the heat radiated by the planet surfaces. Without these gases, the planets would be the temperatures expected as a result of their distance from the Sun. Note: The high concentration of CO2 in the Venusian atmosphere (98% CO2) has led to a "runaway greenhouse effect" and resulted in a surface temperature of about 450 °C!

38. Consider the Lewis structures for SO2. How do they compare with the Lewis structures for ozone?

With respect to valence electron distribution, the Lewis structures of SO2 and ozone are identical. This should not be surprising, as sulfur and oxygen are in the same group on the periodic table, and thus have the same number of outer electrons. However, the atoms present in the two Lewis structures differ:

21. Silver has an atomic number of 47. a. Give the number of protons, neutrons, and electrons in a neutral atom of the most common isotope, Ag-107. b. How do the numbers of protons, neutrons, and electrons in a neutral atom of Ag-109 compare with those of Ag-107?

a. A neutral atom of Ag-107 has 47 protons, 60 neutrons, and 47 electrons. b. A neutral atom of Ag-109 has 47 protons, 62 neutrons, and 47 electrons. Only the number of neutrons is different.

7. Using the periodic table as a guide, specify the number of valence electrons for each of these elements. a. oxygen (O) b. magnesium (Mg) c. nitrogen (N) d. sulfur (S)

a. A neutral atom of oxygen has eight protons and eight electrons. b. A neutral atom of magnesium has 12 protons and 12 electrons. c. A neutral atom of nitrogen has seven protons and seven electrons. d. A neutral atom of sulfur has 16 protons and 16 electrons.

1. In these diagrams, two different types of atoms are represented by color and size. Characterize each sample as an element, a compound, or a mixture. Explain your reasoning.

a. Compound (two molecules of one compound made up of two different elements). b. Mixture (two atoms of one element plus two atoms of another). c. Mixture (three different substances, two elements and one compound). d. Element (four atoms of the same element).

25. a. Can a molecule that contains hydrogen be classified as a CFC? b. What is the difference between an HCFC and an HFC?

a. No, a CFC molecule can contain only chlorine, fluorine, and carbon atoms. b. HCFC molecules must contain hydrogen, carbon, fluorine, and chlorine atoms, and no other atoms. In order for a molecule to be classified as an HFC, it must contain hydrogen, fluorine, and carbon (but no other atoms).

2. Some of the gases found in the troposphere are Rn, CO2, CO, O2, Ar, and N2. a. Rank them in order of their abundance in the troposphere. b. For which of these gases is it convenient to express concentration in parts per million? c. Which of these gases is/are currently regulated as an air pollutant where you live? d. Which of these gases is/are found in Group 8 of the periodic table, the noble gases?

a. Rn < CO < CO2 < Ar < O2 < N2 b. CO and CO2 c. CO. By the time this book is in print, CO2 may be regulated as well. d. Rn (radon) and Ar (argon)

6. a. What is a Dobson unit? b. Does a reading of 320 DU or 275 DU indicate more total column ozone overhead?

a. The Dobson unit (DU) measures the ozone in a column above a specific location on Earth. If this ozone were compressed at specified conditions of temperature and pressure, it would form a layer. A layer 3-mm thick corresponds to 300 DU. Similarly, a 1-mm layer corresponds to 100 DU. b. 320 DU > 275 DU. Thus, 320 DU indicates more total ozone overhead.

5. Gases found in the atmosphere in small amounts include Xe, N2O, and CH4. a. What information does each chemical formula convey about the number and types of atoms present? b. Write the names of these gases.

a. The chemical formula tells the elements present in a compound and the atomic ratio of the elements. b. Xe (xenon), N2O (dinitrogen monoxide or nitrous oxide), CH4 (methane)

6. a. It is estimated that 29 megajoules per square meter (MJ/m2) of energy comes to the top of our atmosphere from the Sun each day, but only 17 MJ/m2 reaches the surface. What happens to the rest? b. Under steady-state conditions, how much energy would leave the top of the atmosphere?

a. The rest of the Sun's energy is either absorbed or reflected by the atmosphere. For example, Chapter 3 pointed out that oxygen and stratospheric ozone absorb certain wavelengths of UV light. This chapter points out that clouds may reflect incoming radiation back into space. b. Under steady-state conditions, 29 MJ/m2 would leave the atmosphere each day.

46. Here are two scanning electron micrograph images of particulate matter, courtesy of the National Science Foundation and researchers at Arizona State University. The first is of a soil particle and the second of a rubber particle, and each is about 10 μm in diameter. (both) Source: Hua Xin, Ph.D., Arizona State University/National Science Foundation a. Suggest a likely source of the rubber particle. Name two other substances that might contribute PM to the air. b. The soil particle is composed mainly of silicon and oxygen. What other elements are commonly present in the rocks and minerals in Earth's crust? c. What about these photographs suggests that these particles would inflame your blood vessels?

a. The rubber may have come from tires abrading as they roll along the highways. Other sources of PM include soot from incomplete combustion and dirt picked up and blown by the wind. b. Iron, aluminum, and calcium also are commonly present. Other possibilities include sodium, potassium, magnesium, and sulfur. c. The edges of the particles appear to be irregular and jagged, thus likely to cause inflammation.

14. Use Figure 3.4 to specify the region of the electromagnetic spectrum where radiation of each of the following wavelengths is found. Hint: Change each wavelength to meters before making the comparison. a. 2.0 cm b. 50 µm c. 400 nm d. 150 mm

a. This wavelength is in the microwave region of the spectrum. b. This wavelength is in the infrared region of the spectrum. c. This wavelength is in the range of violet light in the visible region. d. This wavelength is in the UHF/microwave region of the spectrum.

10. Consider this representation of the reaction between nitrogen and hydrogen to form ammonia (NH3). a. Are the masses of reactants and products the same? Explain. b. Are the numbers of molecules of reactants and of products the same? Explain. c. Are the total number of atoms in the reactants and the total number of atoms in the products the same? Explain.

a. Yes, the mass of the reactants equals the mass of the products. The law of conservation of mass applies. b. No, the numbers of molecules are not the same (four reactant molecules vs. two product molecules). c. Yes, the numbers of each type of atom present as reactants and products are the same.

9. Give the name and symbol for an element with this number of valence electrons. a. 2 b. 8 c. 6

a. helium, He b. potassium, K c. copper, Cu

10. Classify each of these substances as either a homogeneous or heterogeneous mixture. a. a glass of orange juice b. a chocolate chip cookie c. a piece of pizza d. a sample of vinegar e. a sample of beach sand

a. homogeneous mixture if pulp-free b. heterogeneous mixture c. heterogeneous mixture d. homogeneous mixture e. heterogeneous mixture

20. A carbon monoxide detector will go off if the concentration of CO is 400 ppm or greater for a period of 4-15 minutes. a. Express 400 ppm as a percent. b. Why is carbon monoxide considered to be an air pollutant? c. What are the health effects resulting from long-term exposure to carbon monoxide?

b. Carbon monoxide is an air pollutant because when breathed into the lungs, CO can be hazardous to human health. c. Carbon monoxide interferes with the ability of hemoglobin to carry oxygen throughout your body. Exposure to CO in high enough concentrations can cause a person to die due to lack of oxygen. Shorter-term exposure leads to dizziness or a headache.

1. a. Calculate the volume of air in liters that you might inhale (and exhale) while you are sleeping for 7.5 hours. Assume that each breath has a volume of about 0.5 L, and that you are breathing 10 times per minute. b. From this calculation, you can see that breathing exposes you to a large volume of air. Name five things you can do to improve the quality of the air you and others breathe.

b. Possibilities include burning less (wood, vegetation, cooking fuels, gasoline, incense), using products that pollute less (low-emission paints), and using motor-less appliances and tools (hand lawnmower, eggbeater, broom, rake).