Chem 121 - Problem Set 2
1. Fill in the blanks in the following table. Keep in mind that isotope represented may not be the most
common.
Atomic Symbol
Atomic Number
B
Protons
Neutrons
S~
6
<=r
/O^
n
//
/$&
31
y
31
31
Ou
29
IC
Pb
Yb
Electrons
3
37
Atomic Mass
sr
//
3/
39
//
14
G$
3*7
^D
2?
25
<?-?
sv
5?
y3
&Z.
^o
207
y3
43
82.
g> ^
/Zi5~
TO
J-o
SO 2.
89
100
172
X Tell what is wrong with each of the following formulas. Write the correct formula.
(a) HSH (hydrogen sulfide)
(b) HCL02 (chlorus acid)
(c) 2HN2 (hydrazine - two hydrogen atoms and four nitrogen atoms)
^ Silver exists as 51.84% 107Ag and 48.16% 109Ag. The mass of 107Ag is 106.90509 amu and the mass of
109Ag is 108.90476 amu. What is average atomic mass of silver?
*£. Write the following using the notation ^X:
(a) has 59 protons and 82 neutrons
(b) has a mass number of 172 and 102 neutrons
(c) has 2 protons and 2 neutrons
ov Describe each of the following:
(a) electron
(b) neutron
(c) proton
^§L Refer to the periodic table and determine how many grams of sulfur contain the same number of atoms
as 3.10 grams of phosphorus.
^ Determine the following:
(a) The number of grams of silicon in 1.25 mol of silicon
(b) The mass in grams of one calcium atom
(c) The number of argon atoms in a 20.5 g sample of argon
X How do the terms "molar mass" and "atomic mass" differ from each other?
"$l What is the molar mass of the follow:
(a) MgO
(b) CH3CH2OH
(c) C!2H220il (sucrose) ^\l^ll°i\
TO. How much does 4.2 mol of Ca(N03)2 weigh?
K^. How many grams are there in 3.4xl024 molecules of CH4?
^2,. Refer to the periodic table and calculate the molecular weights for the compounds PH3 and S02. Then,
determine how many grams of PH3 contain the same number of molecules as 6.41 g of SO2.
13. Urea (CH4N2O) and ammonium sulfate (N2H8SO4) are both used as agricultural fertilizers. Which ones
contains the higher mass percentage of nitrogen?