The nucleus of 6Li is a powerful absorber of neutrons. It exists in the naturall
ID: 1010956 • Letter: T
Question
The nucleus of 6Li is a powerful absorber of neutrons. It exists in the naturally occurring metal to the extent of 7.5%. In the era of nuclear deterrence, large quantities of lithium were processed to remove 6Li for use in hydrogen bomb production. The lithium metal remaining after removal of 6Li was sold on the market.
a)What are the compositions of the nuclei of 6Li? How many neutrons does 6Li have? Express your answer as an integer.
b)What are the compositions of the nuclei of 6Li? How many protons does 6Li have? Express your answer as an integer.
c)What are the compositions of the nuclei of 7Li? How many neutrons does 7Li have? Express your answer as an integer.
d)What are the compositions of the nuclei of 7Li? How many protons does 7Li have? Express your answer as an integer.
e)The atomic masses of 6Li and 7Li are 6.015122 and 7.016004 amu, respectively. A sample of lithium depleted in the lighter isotope was found on analysis to contain 1.442% 6Li. What is the average atomic weight of this sample of the metal? Express your answer using four significant figures.
Explanation / Answer
(a): For an atom, Mass number = number of protons + number of neutrons
Also atomic number = number of protons.
The atomic number of Li is 3. Hence number of protons in 6Li are 3.
Mass number = number of protons + number of neutrons
=> 6 = 3 + number of neutrons
=> number of neutrons = 6 - 3 = 3 (answer)
(b): Since the atomic number of Li is 3, 6Li has 3 protons (answer)
(c): Mass number = number of protons + number of neutrons
=> 7 = 3 + number of neutrons
=> number of neutrons = 7 - 3 = 4 (answer)
(d): Since the atomic number of Li is 3, 7Li has 3 protons (answer)
(e): Average atomic weight = M1xA1 + M2xA2
where M1 and M2 are atomic masses. A1 and A2 are fractional abundances of isotopes.
=> Average atomic weight = 6.015122 amu x 0.01442 + 7.016004 amu x (1 - 0.01442)
=> Average atomic weight = 6.015122 amu x 0.01442 + 7.016004 amu x 0.98558
=> Average atomic weight = 7.001571 amu (answer)
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