Chapter 3 Review packet 1

# The atomic masses in the periodic table are not

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21. The atomic masses in the periodic table are not integral numbers. For example, carbon is listed as 12.01115 instead of 12.00000. Why? a. Our technology does not allow for exact measurement of such a small quantity. b. Atoms gain and lose electrons easily and that changes their masses significantly. c. Atomic masses listed in the periodic table are weighted averages of isotopic masses. d. Atomic masses are measured in real samples that are always contaminated with other elements. e. There is a theoretical uncertainty in the masses of atoms. 22. Given the information below, calculate the weighted average atomic mass (amu) of the element X. Isotope Abundance (%) Mass(amu) 221 X 74.22 220.9 220 X 12.78 220.0 218 X 13.00 218.1 23. Element X has three naturally occurring isotopes. The mass (amu) and % abundance of the isotopes are: 37.919 (5.07%), 39.017 (15.35%), and 42.111 (79.58%). What is the average atomic mass (amu) of element X? 24. The mass % of C in CH 4 is __________.

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25. Which of the following, strictly speaking, does not have a molecular weight? a. SO 2 b. CH 4 c. H 2 O d. Li 2 S e. each of these has a molecular weight 26. There are __________ mol of carbon atoms in 4 mol of dimethylsulfoxide (C 2 H 6 SO). 27. How many hydrogen atoms are there in 25 molecules of C 4 H 4 S 2 ? 28. How many molecules of CH 4 are in 48.2 g of this compound? 29. A sample of CH 2 F 2 with a mass of 19 g contains __________ atoms of F. a. 2.2 x 10 23 b. 38 c. 3.3 x 10 24 d. 4.4 x 10 23 e. 9.5 30. How many oxygen atoms are contained in 2.74 g of Al 2 (SO 4 ) 3 ? 31. What is the empirical formula of a compound that contains 27.0% S, 13.4% O, and 59.6% Cl?
32. What is the empirical formula of a hydrocarbon that is 89.94% by mass carbon? 33. What is the empirical formula for a compound that contains 29% Na, 41% S, and 30% O by mass? a. Na 2 S 2 O 3 b. NaSO 2 c. NaSO d. NaSO 3 e. Na 2 S 2 O 6

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