Chem 27 Chapter 20
EOC (Question 37) The most stable nucleus in terms of binding energy per nucleon is Fe-56. If the atomic mass of Fe-56 is 55.9349 u, calculate the binding energy per nucleon for Fe-56.
1.408 × 10^−12 J/nucleon Explanation: *See IPad/EOC Solutions
EOC (Question 24) A chemist wishing to do an experiment requiring Ca-47^2+ (half-life=4.5 days) needs 5.0 mg of the nuclide. What mass of CaCO3-47 must be ordered if it takes 48 h for delivery from the supplier? Assume that the atomic mass of Ca-47 is 47.0 u.
15 ug CaCO3-47 Explanation: *See IPad
EOC (Question 21) The first atomic explosion was detonated in the desert north of Alamogordo, New Mexico, on July 16, 1945. What percentage of the strontium-90 (t1/2 5 28.9 yr) originally produced by that explosion still remains as of July 16, 2016?
18.3% Explanation: See IPad
Quiz 4 (Lecture) Each of the following nuclear reactions is missing some information. Use the rules and principles taught in class to determine the only (or most likely) possibility. *See IPad Since I cannot do sub/superscripts in matching problems, names have to be written out. For example uranium-238, where the 92 is implied by the U (it is redundant).
A. Chlorine-35+electron B. Silicon-30+positron C. Alpha particle D. Electron E. Strontium-90 F. Plutonium-239
Knewton (Half-Lives) Use the periodic table below to answer the question that follows. Which of the following has the longest half-life? A. F-19 B. Co-60 C. I-131 D. TI-201
A. F-19 Explanation: The only isotope of these four that is not radioactive is F-19. The other three isotopes are important radioactive isotopes used in medicine, while F-19 is a stable isotope of fluorine, so its half-life is essentially limitless.
Knewton (Radioactive Decay) Alpha particle emission is most likely to occur if a nucleus: A. Is too large B. has a neutron to proton ratio that is too large C. Has a neutron to proton ratio that is too small D. Is excited
A. Is too large Explanation: If a nucleus is simply too large to be stable, it is likely to undergo alpha particle emission, which decreases the mass of the nucleus by 4.
Quiz 4 (Reading) The binding energy of Fe-56 (check all that apply) A. is related to the mass defect by a factor of c^2 B. is the energy released per nucleon when formed from 26 protons and 30 neutrons. C. has the largest magnitude of all nuclides.
A. is related to the mass defect by a factor of c^2 B. is the energy released per nucleon when formed from 26 protons and 30 neutrons. C. has the largest magnitude of all nuclides.
Quiz 5 (reading) Make the best set of matches between the following terms and associated concepts. A. rem B. critical mass C. Geiger counter D. nuclear fusion E. radiotracers F. radioactive dating G. radiation therapy H. nuclear bomb I. breeder reactor
A. rem - unit of radiation exposure B. critical mass - amount of fissile material necessary for a chain reaction C. Geiger counter - device used to measure radioactivity D. nuclear fusion - a potential energy source that is difficult to harness E. radiotracers - make use of chemical and radioactive properties for medical diagnostics F. radioactive dating - application of first order kinetics to measure time G. radiation therapy - selective destruction of bodily tissues H. nuclear bomb - uncontained release of nuclear energy and radioactive material I. Breeder reactor - a fission reactor that creates more fuel than it consumes
Quiz 4 (Reading) Which quantities must be conserved in all nuclear transformations? A. sum of mass numbers B. total mass C. total charge
A. sum of mass numbers C. total charge
Knewton (Nuclear Structure and Stability) Identify the options below that can be determined from a nuclide symbol. Select all that apply. A. The charge of the nuclide B. The atomic number of the nuclide C. The number of protons in the nuclide D. The number of isotopes of that element
B. The atomic number of the nuclide C. The number of protons in the nuclide Explanation: The chemical symbol, atomic number, and mass number of an element are included in a nuclide symbol.
Knewton (Nuclear Equations) The mass of an alpha particle is given by which of the following? (select all that apply) A. 1 B. The same as that of a He nucleus C. 4 D. The same as that of a H nucleus
B. The same as that of a He nucleus C. 4 Explanation: The mass of an alpha particle is equivalent to that of a helium nucleus: 4 amu.
Knewton (Nuclear Equations) Use the periodic table below to answer the question that follows. What kind of decay must magnesium-23 undergo to generate sodium-23? A. alpha particle emission B. beta particle emission C. positron emission D. gamme emission
C. positron emission Explanation: In order for magnesium-23 to become sodium-23, the atomic number must decrease by 1 while the mass remains unchanged. This can be accomplished by the transformation of a proton into a neutron, which results in positron emission in order to conserve the overall charge.
Knewton (Half-Lives) Carbon-14 primarily enters living organisms in the form of... Enter a molecular formula.
CO2 Plants absorb carbon dioxide (CO2) in the process of photosynthesis, of which a small percentage of its carbon is present as Carbon-14.
Knewton (Half-Lives) Use the periodic table below to answer the question that follows. Which of the following CANNOT be used in radiometric dating? A. Uranium-238 B. Potassium-40 C. Carbon-14 D. Nitrogen-14
D. Nitrogen-14 Explanation: Nitrogen-14 is a stable nucleus; it does not decay at all. The amount of N-14 in any sample will remain constant until the end of time, so this nuclide cannot be used to determine the age of a sample.
Knewton (Half-Lives) In radiocarbon dating, what is actually measured? A. Grams of carbon B . Number of disintegrations per minute C. Number of disintegrations per gram of carbon D. Number of disintegrations per minute per gram carbon
D. Number of disintegrations per minute per gram carbon Explanation: Radiocarbon dating involves counts of disintegrations that happen per minute, per gram of carbon. This is a standardized unit of measurement across samples of various sizes.
Knewton (Nuclear Equations) A γ particle is a(n): Select the correct answer below: A. Proton B. Neutron C. Electron D. Photon
D. Photon Explanation: A γ particle is a type of photon (a form of light radiation).
Knewton (Half-Lives) Use the periodic table below to answer the question that follows. Which of the following has the longest half-life? Select the correct answer below: A. O-19 B. H-3 C. Zn-71 D. Rb-85
D. Rb-85 Explanation: Rubidium-85 is the only stable isotope listed here; thus this nucleus must have the longest half-life.
Knewton (Nuclear Structure and Stability) Use the periodic table below to answer the question that follows. Which nuclide would have the greatest mass defect? A. F-19 B. C-12 C. Be-9 D. S-32
D. S-32 Explanation: Mass defect increases as more particles are added to the nucleus, so sulfur (being the largest nucleus in this list) will have the greatest mass defect.
EOC (Question 41) The binding energy per nucleon for magnesium-27 is 1.326 x 10^-12 J/nucleon. Calculate the atomic mass of magnesium-27.
mMg = 26.9764 u Explanation: *Remember when calculating for mass difference, reverse kg to g and avagadro's number and u to where it is (1000g/1 kg and 6.022 x 10^23/1u) *See IPad/EOC Solutions
EOC (Question 4) Write an equation describing the radioactive decay of each of the following nuclides. (The particle produced is shown in parentheses, except for electron capture, where an electron is a reactant.) A. H-3 (B) B. Li-8 (B followed by an alpha particle) C. Be-7 (electron capture) D. B-8 (positron)
*See IPad
EOC (Question 7) Write an equation describing the radioactive decay of each of the following nuclides. (The particle produced is shown in parentheses, except for electron capture, where an electron is a reactant.) A. Ga-68 (electron capture) B. Cu-62 (positron) C. Fr-212 (alpha particle) D. Sb-129 (B)
*See IPad
Knewton (Nuclear Equations) Use the periodic table below to answer the question that follows. If radium-226 undergoes alpha particle emission, what nucleus is produced? Enter your response using the elemental symbol followed by a dash and then the mass number for the nucleus produced. For example He−4.
*See IPad
Knewton (Half-Lives) If a substance has a half-life of 39.1 min, and there are initially 20.0 g of the substance, how many grams will remain after precisely two hours? Report your answer with three significant figures.
2.39g Explanation: See IPad
Knewton (Nuclear Structure and Stability) How many neutrons are in Br-79
44
Knewton (Nuclear Equations) Given that the positron is the antimatter equivalent of an electron, what is its approximate atomic mass? Select the correct answer below: A. 0 B. 1 C. -1 D. None of the above
A. 0 Explanation: A positron has the same mass as an electron, which is approximately (0 amu).
Knewton (Nuclear Structure and Stability) For small nuclei, the preferred neutron to proton ratio is approximately: A. 1:1 B. 1.5: 1 C. 1: 1.5 D. 2: 1
A. 1:1 Explanation: For small nuclei (i.e. those in the first two rows of the periodic table), a 1:1 ratio of neutrons to protons is preferred. Examples include the most stable isotopes of carbon (C-12), nitrogen (N-14), and oxygen (O-16).
Knewton (Nuclear Structure and Stability) Nuclear fusion always results in: A. A net loss of mass B. A net gain of mass C. No change in mass (mass is conserved) D. Depends on the nucleons that fuse
A. A net loss of mass Explanation: When the nucleons fuse together, a fraction of their mass is always lost.
Knewton (Nuclear Structure and Stability) Which carbon nucleus is predicted to be most stable? A. C-12 B. C-13 C. C-14 D. C-11
A. C-12 Explanation: In general, the stablest isotopes of lighter elements (like carbon) have equal numbers of protons and neutrons. Because the numbers of protons and neutrons are the same in C-12, this nucleus is expected to be most stable isotope of carbon. The natural abundance of this isotope is about 99%.
Knewton (Nuclear Structure and Stability) In E=mc^2, c denotes A. The speed of light B. The charge of the substance in question C. The heat capacity of the substance in question D. The speed of the substance in question
A. The speed of light In this equation, c denotes the speed of light in a vacuum, 3.0×10^8 m/s. (2.997 x 10^8 m/s)
Knewton (Nuclear Structure and Stability) Of the following, which are true of nuclei that are to the left or right of the band of stability? (select all that apply) A. They are known as radioisotopes B. They do not undergo nuclear decay C. They are considered stable D. They undergo nuclear decay
A. They are known as radioisotopes D. They undergo nuclear decay Explanation: Nuclei that lie to the left or right of the band of stability are unstable; they are radioisotopes that decay into other nuclei that are in (or closer to) the band of stability.
Knewton (Nuclear Equations) What is the superscript in the symbol for the positron? Select the correct answer below: A. -1 B. 0 C. 1 D. 2
B. 0 Explanation: The superscript denotes the mass of the positron, which is so small relative to that of protons and neutrons that we consider it to be massless. Thus the superscript in the symbol for the positron is 0.
Knewton (Nuclear Structure and Stability) Use the periodic table below to answer the question that follows. Which of the following is most likely a heavier stable nucleus? (select all that apply) A. A nucleus with a neutron: proton ratio of 1.05 B. A nucleus with a neutron proton ratio of 1.49 C. The nucleus of Sb-123 D. The nucleus with a mass of 187 and an atomic number 75
B. A nucleus with a neutron proton ratio of 1.49 C. The nucleus of Sb-123 D. The nucleus with a mass of 187 and an atomic number 75 Explanation: A heavier stable nucleus usually has a neutron:proton ratio close to 1.5.
Knewton (Nuclear Structure and Stability) Which of the following is included in nuclide symbols, but is not strictly necessary for the identification of the nuclide? A. Mass number B. Atomic number C. Isotope number D. None of the above
B. Atomic number Explanation: The chemical symbol, atomic number, and mass number of the atom are included in a nuclide symbol. However, the atomic number of the nuclide is implied by its chemical symbol, so we do not actually need the nuclide's atomic number to identify it.
Knewton (Radioactive Decay) The term electron capture best fits which of the following descriptions? A. Electron capture is a phenomenon exhibited by an unstable nucleon that spontaneously converts into more stable nuclei B. Electron capture is the combination of a core electron with a proton to yield a neutron with the nucleus C. Electron capture is the addition of an electron to a neutral atom to form an anion D. None of the above
B. Electron capture is the combination of a core electron with a proton to yield a neutron with the nucleus Explanation: Electron capture is defined as the combination of a core electron with a proton to yield a neutron within the nucleus. (See textbook *different definition)
Knewton (Radioactive Decay) Which of the following is true of electron capture? A. It decreases the nuclide's mass number by 2 B. It is most likely to occur when the neutron: proton ratio of the nuclide is too small C. It is most likely to occur when the nuclide is formed in an excited state D. It is most likely to occur when the neutron:proton ratio of the nuclide is too large
B. It is most likely to occur when the neutron: proton ratio of the nuclide is too small Explanation: Refer to textbook table If there are too many protons in a nucleus, electron capture can occur. This involves the conversion of a proton into a neutron, which decreases the nuclide's atomic number by 1 and increases its neutron:proton (n:p) ratio.
Knewton (Nuclear Structure and Stability) Nuclear binding energies for the fusion of a mole of nuclei typically correspond to mass differences on the order of: A. Grams B. Milligrams C. Micrograms D. Nanograms
B. Milligrams Explanations: Nuclear binding energies are on the order of billions of kilojoules per mole, which typically correspond to mass differences in the milligram range.
Knewton (Nuclear Structure and Stability) Use the periodic table below to answer the question that follows. Given that the magic numbers for protons/neutrons are 2, 8, 20, 28, 50, 82, and 126, which of the following are double magic nuclei? A. Ni-62 B. O-16 C. Ca-48 D. Ni-78
B. O-16 C. Ca-48 D. Ni-78 Explanation: Double magic nuclei have a magic number of both neutrons and protons. O-16 (8 and 8), Ca-48 (20 & 28), and Ni-78 (28 and 50) are all examples of double magic nuclei. Ni-48, is another example of a double magic nucleus. Ni-62 is not because wile it has 28 protons, it has 34 neutrons.
(EOC #2) Which type of radioactive decay has the net effect of changing a neutron into a proton? Which type of decay has the net effect of turning a proton into a neutron?
Beta-particle production has the net effect of turning a neutron into a proton. Radioactive nuclei having too many neutrons typically undergo beta-particle decay. Positron production has the net effect of turning a proton into a neutron. Nuclei having too many protons typically undergo positron decay.
Quiz 5 (lecture) From Wikipedia: Large amounts of otherwise rare Cl-36 were produced by irradiation of seawater during atmospheric detonations of nuclear weapons between 1952 and 1958. Thus, as an event marker of 1950s water in soil and ground water, Cl-36 is also useful for dating waters less than 50 years before the present. Chlorine-36 has a half-life of 3.0×10^5 years. How long does it take for 1.0% of the Cl-36 in a sample to decay? A. 3.0×10^5 yr B. 2.0×10^5 yr C. 4.3×10^3 yr D. 6.1×10^2 yr E. 50 yr F. 3.4×10^−8 yr
C. 4.3×10^3 yr Explanation: *See IPad
Knewton (Nuclear Structure and Stability) What is the approximate value of nuclear mass that exhibits the greatest stability? A. 10 B. 28 C. 56 D. 82
C. 56 Explanation: A nucleus with a mass number of approximately 56 is calculated to have the greatest binding energy per nucleon.
Knewton (Nuclear Structure and Stability) The mass of a nuclide is typically symbolized by which of the following? A. m B. M C. A D. Z
C. A Explanation: Mass number has the symbol A in a nuclide symbol.
Knewton (Nuclear Structure and Stability) Identify the options below that are most likely lighter stable nuclei. (select all that apply) A. A nucleus with a neutron:proton ratio of 2.0 B. A nucleus with a neutron:proton ratio of 1.51 C. A nucleus with a neutron: proton ratio of 1.0 D. A nucleus with an atomic mass number of 32 and an atomic number of 16
C. A nucleus with a neutron: proton ratio of 1.0 D. A nucleus with an atomic mass number of 32 and an atomic number of 16 Explanation: A lighter stable nucleus usually has a neutron:proton ratio close to 1.
Knewton (Nuclear Structure and Stability) Nuclear binding energies are typically on the order of: A. Hundreds of kJ/mol B. Thousands of kJ/mol C. Billions of kJ/mol D. They are too small to be measured
C. Billions of kJ/mol Explanation: Most nuclei contain very large nuclear binding energies, on the order of 1,000,000,000 kJ/mol
Knewton (Radioactive Decay) During nuclear decay, the resulting nucleus after emission has occurred is called the: A. Resultant nucleus B. Offspring nucleus C. Daughter nucleus D. Product nucleus
C. Daughter nucleus Explanation: The nucleus, after decay, is referred to as the daughter nucleus.
Knewton (Nuclear Structure and Stability) Which is the term for the repulsive force between charged nucleons? Select the correct answer below: A. Strong nuclear force B. Weak nuclear force C. Electromagnetic force D. There is no repulsion between nucleons
C. Electromagnetic force Explanation: Nucleons are either neutrons or protons. Neutrons have no charge and protons are positively charged; therefore, a charge nucleon is necessarily a proton. Electromagnetic forces causes like charges to repel, including the protons in a nucleus.
Knewton (Nuclear Structure and Stability) E=mc^2 is also known as the: A. Nuclear mass conversion equation B. Nuclear energy conversion factor C. Mass-energy equivalence relation D. None of the above
C. Mass-energy equivalence relation
Knewton (Nuclear Equations) When balancing nuclear reactions, the mass numbers of the nuclides: A. Must always increase B. Must always decrease C. Must not have a net change D. Depends on the reaction
C. Must not have a net change Explanation: For any nuclear reaction, the sum of the masses (superscripts) of the "reactants" must be equal that of the "products". The law of conservation of mass still applies for most nuclear reactions!
Knewton (Nuclear Structure and Stability) Use the periodic table to answer the question. The magic numbers for protons/neutrons are 2, 8, 20, 28, 50, 82, and 126. Which of the following are double magic nuclei? A. Zr-90 B. Ti-52 C. Ni-48 D. O-16
C. Ni-48 D. O-16 Explanation: Refer to question 33
Quiz 4 (Lecture) The mass of a U-235 nucleus is 234.993454 amu. Compute the binding energy this nuclide. mp = 1.00728 amu mn = 1.00866 amu A. 1790 MeV/nucleon B. 6.81 MeV/nucleon C. 8.10 MeV/nucleon D. 7.60 MeV/nucleon E. 376 MeV/nucleon
D. 7.60 MeV/nucleon Explanation: *See IPad
Knewton (Half-Lives) In addition to Carbon-14, which of these is a nucleus that is used for radiometric dating? A. Fe-50 B. S-32 C. U-238 D. All of the above
C. U-238 Explanation: Uranium-238, with a half life of about 4.5 billion years, can be used to date extremely old rocks. S-32 is a stable nucleus (it never decays), and Fe-50 does not exist.
Knewton (Nuclear Equations) Use the periodic table below to answer the question that follows. What isotope will result if sulfur-35 undergoes B- emission?
Cl-35 Explanation: See IPad
Knewton (Nuclear Structure and Stability) Which description best fits the definition of nuclear reaction? A. Nuclear reaction is the combination of very light nuclei into heavier nuclei, accompanied by the conversion of mass into large amounts of energy B. A nuclear reaction is the separation of a chemical compound into elements of simpler compounds C. A nuclear reaction is the bombardment of one type of nuclei with other nuclei or neutrons D. A nuclear reaction is a change to a nuclear, resulting in changes in its atomic number, mass number, or energy state
D. A nuclear reaction is a change to a nuclear, resulting in changes in its atomic number, mass number, or energy state Explanation: A nuclear reaction is defined as a change in the nucleus of an atom, resulting in changes in its atomic number, mass number, or energy state. It is a change in identity or characteristics of an atomic nucleus that results when it is bombarded with an energetic particle, as in fusion, fission or nuclear decay.
Knewton (Radioactive Decay) γ emission is most likely to occur if a nucleus: A. Is too large B. Has a neutron to proton ratio that is too large C. Has a neutron to proton ratio that is too small D. Is excited
D. Is excited Explanation: If an electron is in an excited state, the emission of a high-energy gamma ray allows the nucleus to relax to the ground state.
Quiz 5 (reading) The kinetics of nuclear decay processes A. may have variable rate, according to the steady-state approximation. B. are always second order. C. depend on the process under discussion. D. are always first order. E. are always zeroth order.
D. are always first order.
Knewton (Half-Lives) Half-life is abbreviated as: A. l1/2 B. lhalf C. thalf D. t1/2
D. t1/2 Explanation: A lower case t with a subscript of 1/2 is the abbreviation for half-life. Half-life is the amount of time it takes for one-half of a radioactive isotope to decay.
Knewton (Half-Lives) If a substance has a half-life of 72.8 min, and if 65.0 g of the substance are initially present, how many grams will remain after precisely three hours? Report your answer with three significant figures.
Explanation: See IPad
EOC (Question 12) There are four stable isotopes of iron with mass numbers 54, 56, 57, and 58. There are also two radioactive isotopes: iron-53 and iron-59. Predict modes of decay for these two isotopes, and write a nuclear reaction for each. (See Table 20.2.)
Fe-53 has too many protons. It will undergo either positron production, electron capture, and/or alpha-particle production. Fe-59 has too many neutrons and will undergo beta-particle production. (See Table 20.2 of the text.) The reactions are: *See IPad
EOC (Question 18) Krypton consists of several radioactive isotopes, some of which are listed in the following table. Kr-73 (Half life: 27s) Kr-74 (Half life: 11.5 min) Kr-76 (Half life: 14.8 hr) Kr-81 (2.1 x 10^5 yr) Which of these isotopes is most stable, and which isotope is "hottest"? How long does it take for 87.5% of each isotope to decay?
Most stable: Kr-81 (Longest half-life) Hottest: Kr-73 (Shortest half-life) *See IPad for part 3
Knewton (Nuclear Equations) Use the periodic table below to answer the question that follows. Radium-221 will undergo alpha decay according to the following equation. What is the atomic symbol for the unknown nuclide?
Rn where A=217 and where B=86 Explanation: Refer to question 13
EOC (Question 32) The sun radiates 3.9 3 10^23 J of energy into space every second. What is the rate at which mass is lost from the sun?
The sun loses 4.3 × 10^6 kg of mass each second. Note: 1 J = 1 kg m^2/s^2. Explanation: *See IPad/EOC Solutions
EOC (Question 27) At a flea market you've found a very interesting painting done in the style of Rembrandt's "Dark Period" (1642- 1672). You suspect that you really do not have a genuine Rembrandt, so you take it to the local university for testing. Living wood shows a carbon-14 activity of 15.3 counts per minute per gram. Your painting showed a carbon-14 activity of 15.1 counts per minute per gram. Could it be a genuine Rembrandt? (For C-14, t1/2=5730 years.)
t=109 yrs No; from C-14 dating, the painting was produced during the early 1900s. Explanation: See IPad/EOC solutions
EOC (Question 32) A proposed system for storing nuclear wastes involves storing the radioactive material in caves or deep mine shafts. One of the most toxic nuclides that must be disposed of is plutonium-239, which is produced in breeder reactors and has a half-life of 24,100 years. A suitable storage place must be geologically stable long enough for the activity of plutonium-239 to decrease to 0.1% of its original value. How long is this period for plutonium-239?
t=200,00 yrs Explanation: *See IPad/EOC Solutions