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الكيمياء الصناعية | Chemistry Is Everywhere: Sulfur Hexafluoride |
 906
 06:09 مساءً
date: 2-11-2020 |
Author : University of Missouri System 
Book or Source : Organic Chemistry ii 
Page and Part : .................|
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Date: 6-9-2020
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On March 20, 1995, the Japanese terrorist group Aum Shinrikyo (Sanskrit for “Supreme Truth”) released some sarin gas in the Tokyo subway system; twelve people were killed, and thousands were injured (part (a) in the accompanying figure). Sarin (molecular formula C4H10FPO2) is a nerve toxin that was first synthesized in 1938. It is regarded as one of the most deadly toxins known, estimated to be about 500 times more potent than cyanide. Scientists and engineers who study the spread of chemical weapons such as sarin (yes, there are such scientists) would like to have a less dangerous chemical, indeed one that is nontoxic, so they are not at risk themselves.
Sulfur hexafluoride is used as a model compound for sarin. SF6 (a molecular model of which is shown in part (b) in the accompanying figure) has a similar molecular mass (about 146 u) as sarin (about 140 u), so it has similar physical properties in the vapour phase. Sulfur hexafluoride is also very easy to accurately detect, even at low levels, and it is not a normal part of the atmosphere, so there is little potential for contamination from natural sources. Consequently, SF6 is also used as an aerial tracer for ventilation systems in buildings. It is nontoxic and very chemically inert, so workers do not have to take special precautions other than watching for asphyxiation.
Sulfur hexafluoride also has another interesting use: a spark suppressant in high-voltage electrical equipment. High-pressure SF6 gas is used in place of older oils that may have contaminants that are environmentally unfriendly (part (c) in the accompanying figure).
Define atomic mass unit. What is its abbreviation?
Define atomic mass. What is its unit?
Estimate the mass, in whole numbers, of each isotope.
a) hydrogen-1
b) hydrogen-3
c) iron-56
4. Estimate the mass, in whole numbers, of each isotope.
a) phosphorus-31
b) carbon-14
c) americium-241
5. Determine the atomic mass of each element, given the isotopic composition.
a) lithium, which is 92.4% lithium-7 (mass 7.016 u) and 7.60% lithium-6 (mass 6.015 u)
b) oxygen, which is 99.76% oxygen-16 (mass 15.995 u), 0.038% oxygen-17 (mass 16.999 u), and 0.205% oxygen-18 (mass 17.999 u)
6. Determine the atomic mass of each element, given the isotopic composition.
a) neon, which is 90.48% neon-20 (mass 19.992 u), 0.27% neon-21 (mass 20.994 u), and 9.25% neon-22 (mass 21.991 u)
b) uranium, which is 99.27% uranium-238 (mass 238.051 u) and 0.720% uranium-235 (mass 235.044 u)
7. How far off would your answer be from Exercise 5a if you used whole-number masses for individual isotopes of lithium?
8. How far off would your answer be from Exercise 6b if you used whole-number masses for individual isotopes of uranium?
9. What is the atomic mass of an oxygen atom?
10. What is the molecular mass of oxygen in its elemental form?
11. What is the atomic mass of bromine?
12. What is the molecular mass of bromine in its elemental form?
13. Determine the mass of each substance.
a) F2
b) CO
c) CO2
14. Determine the mass of each substance.
a) Kr
b) KrF4
c) PF5
15. Determine the mass of each substance.
a) Na
b) B2O3
c) S2Cl2
16. Determine the mass of each substance.
a) IBr3
b) N2O5
c) CCl4
17. Determine the mass of each substance.
a) GeO2
b) IF3
c) XeF6
18. Determine the mass of each substance.
a) NO
b) N2O4
c) Ca
Answers
1.
The atomic mass unit is defined as one-twelfth of the mass of a carbon-12 atom. Its abbreviation is u.
3.
a) 1
b) 3
c) 56
5.
a) 6.940 u
b) 16.000 u
7.
We would get 6.924 u.
9.
a) 15.999 u
b) 31.998 u
11.
a) 37.996 u
b) 28.010 u
c) 44.009 u
13.
a) 22.990 u
b) 69.619 u
c) 135.036 u
15.
a) 104.64 u
b) 183.898 u
c) 245.281 u
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