CH 221 Practice Problem Set #2
This is a practice problem set and not the actual graded problem set that you will turn in for credit.
Answers to each problem can be found at the end of this assignment.
Covering: Chapter Two, Chapter 3.1 and Chapter Guide Two
Important Tables and/or Constants: 1 mol = 6.022 x 1023
1. Give the mass number of each of the following atoms: a. magnesium with 15 neutrons, b.
titanium with 26 neutrons, and c. zinc with 32 neutrons.
2. Give the complete symbol ( ) for each of the following atoms: a. potassium with 20
neutrons, b. krypton with 48 neutrons, and c. cobalt with 33 neutrons.
3. Thallium has two stable isotopes, 203Tl and 205Tl. Knowing that the atomic weight of thallium
is 204.4, which isotope is the more abundant of the two?
4. Silver (Ag) has two stable isotopes, 107Ag and 109Ag. The isotopic mass of 107Ag is 106.9051
and the isotopic mass of 109Ag is 108.9047. The atomic weight of Ag, from the periodic table,
is 107.868. Estimate the percentage of 107Ag in a sample of the element.
a. 0% b. 25% c. 50% d. 75%
5. Gallium has two naturally occurring isotopes, 69Ga and 71Ga, with masses of 68.9257 u and
70.9249 u, respectively. Calculate the percent abundances of these isotopes of gallium.
6. Calculate the mass in grams of:
a. 2.5 mol aluminum b. 1.25 x 10-3 mol of iron!
c. 0.015 mol of calcium d. 653 mol of neon
7. Calculate the amount (moles) represented by each of the following: !
a. 127.08 g of Cu b. 0.012 g of lithium
c. 5.0 mg of americium d. 6.75 g of Al
8. Classify the following elements as metals, metalloids, or nonmetals: N, Na, Ni, Ne, and Np.
9. Fill in the blanks in the table (one column per element):
10. Put the following elements in order from smallest to largest mass:!
a. 3.79 x 1024 atoms Fe b. 19.921 mol H2 c. 8.576 mol C d. 7.4 mol Si
e. 9.221 mol Na f. 4.07 x 1024 24 atoms Al g. 9.2 mol Cl2
11. Dilithium is the fuel for the Starship Enterprise. Because its density is quite low, however,
you need a large space to store a large mass. To estimate the volume required, we shall use
the element lithium. If you need 256 mol for an interplanetary trip, what must the volume of
the piece of lithium be? If the piece of lithium is a cube, what is the dimension of an edge of
the cube? (The density for the element lithium is 0.534 g/cm3 at 20 °C.)
12. A cylindrical piece of sodium is 12.00 cm long and has a diameter of 4.5 cm. The density of
sodium is 0.971 g/cm3. How many atoms does the piece of sodium contain? (The volume of a
cylinder is V = π x r2 x length.)
€
Z
AX
Symbol
58Ni
33S
Number of protons
10
Number of neutrons
10
30
Number of electrons in
the neutral atom
25
Name of the element
Page VI-2- / Practice Problem Set #21
