12/08/16
CHEM 4
Quiz 7 (20 points)
Name
ANSWER KEY
1. (5 points) Fill the blanks in the following table with the information for each atom or
monatomic ion.
Number of Lewis
Name
Symbol
Full Electron Configuration
Unpaired Symbol
Electrons or N/A
phosphorus
1s22s22p63s23p3
3
P
atom
arsenide ion
As3−
1s22s22p63s23p63d104s24p6
0
rubidium ion
Rb+
1s22s22p63s23p63d104s24p6
0
Rb+
manganese(II)
ion
Mn2+
1s22s22p63s23p63d5
5
N/A
Sn2+
1s22s22p63s23p63d104s24p64d105s2
0
[:Sn]2+
Ga
1s22s22p63s23p63d104s24p1
1
tin (II) ion
gallium atom
2. (5 points) The solubility of potassium nitrate in water at 20°C is 31.6 g per 100 g of water.
(a) What is the percent (by mass) concentration of the saturated solution of potassium nitrate?
Show work.
% (m/m) = mass of solute / mass of solution × 100% =
= (31.6 g) / (31.6 g + 100 g) × 100% = 24.0 %
(b) What is the minimum volume of water in mL is required to dissolve 0.750 g of
potassium nitrate at 20°C? Show work.
0.750 g KNO3 × (100 g H2O) / (31.6 g KNO3) = 2.37 g H2O
2.37 g H2O / (1.00 g/mL) = 2.37 mL H2O
(c) What is the molarity of the saturated solution of potassium nitrate? The density of the
solution is 1.16 g/mL. Show work.
31.6 g KNO3 / (101.10 g/mol) = 0.313 mol KNO3
131.6 g solution / (1.16 g/mL) = 113 mL = 0.113 L solution
Molarity = (0.313 mol KNO3) / (0.113 L solution) = 2.77 mo/L or 2.77 M
PLEASE TURN OVER!!!
3. (5 points) Fill the blanks.
The Lewis symbol for
aluminum atom is
The Lewis symbol for
sulfur atom is
.
The Lewis symbol
for aluminum ion is
.
.
The Lewis symbol
for sulfide ion is
.
Give the formula unit of aluminum sulfide as a combination of Lewis symbols for individual
ions:
Al2S3
The formula of aluminum sulfide (symbols and subscripts) is
150.16
The formula mass of aluminum sulfide is
The molar mass of aluminum sulfide is
.
amu.
150.16
g/mol.
One mole of aluminum sulfide contains
6.022×1023
formula units.
One mole of aluminum sulfide contains
1.204×1024
aluminum ions.
One mole of aluminum sulfide contains
1.807×1024
sulfide ions.
4. (5 points) Fill the blanks in the following table.
Formula
Name
Lewis Structure
(single structure or
several resonance
structures;
Dots & Dashes Style)
Name of the Electron
Cloud Geometry
Name of the Geometric
Arrangement of Atoms
SO3
SO32−
SO42−
sulfur trioxide
sulfide ion
sulfate ion
trigonal planar
tetrahedral
tetrahedral
trigonal planar
trigonal pyramidal
tetrahedral
120°
109.5°
109.5°
Drawing of the
Geometric
Arrangement of Atoms
and Lone Pairs around
the Central Atom
Predicted Ideal Bond
Angle