Chemistry 112
First Hour Exam
Name:____________
(4 points)
Please show all work for partial credit
All problems are worth 12 points
Please read and sign the following statement:
I understand that this test is being given over the course of several days. As a
result, I will not discuss the problems on this test with anyone until after Noon on Friday,
September 21.
Signed: ___________________ Date: ______________
1A. How many significant figures are in each of the following numbers?
23030
___4____
2.3030 __5____
.0023030x103 _5______
1B. Below are the answers to different calculations. Express this number with the correct
number of significant figures
23 x 453 = 10419
___1.4x104_______
453-23 = 430
__430.____ (453 and 23 are good to the 1's place)
(23x453) / (453-23) = 24.2302
2. Perform the following unit conversions:
57 nm to km
57 footAlbs to cmAkg
32 lbsAin-2 to kgAm-2
__24________
2
3. Calculate the Molecular mass of the following compounds
Li2O
2(6.941) + 16.00 = 29.88u
Ca(OH)2
40.008 + 2(16.00) + 2(1.008) = 74.096u
Sodium chloride (If you don’t know the formula, make one up for partial credit)
NaCl = 232.99+35.45=58.44u
Sulfur hexafluoride (If you don’t know the formula, make one up for partial credit)
SF6 = 32.07+6(19.00) = 146.07u
4. Complete the following table:
Complete Symbol
# protons
# electrons
# neutrons
6
6
7
13
13
13
25
23
30
7
10
7
3
5. Balance the following chemical reactions:
Ca(s) + O2(g) 6CaO(s)
2Ca(s) + O2(g) 62CaO(s)
Mg3N2(s) + HCl (g)6 MgCl2(s) + NH3(g)
Mg3N2(s) + 6HCl (g)6 3MgCl2(s) + 2NH3(g)
C2H6(g) + O2(g) 6 CO2(g) + H2O(g)
2C2H6(g) + 7O2(g) 6 4CO2(g) + 6H2O(g)
6A. In the blank periodic table below please indicate where the following things are found:
alkali metals XXXX
Nobel or inert gases YYYYY
Second period elements ZZZZ
6B. Using the periodic table supplied with this test please identify the following elements
(A symbol get you 1 point, a full name, correctly spelled gets you 2 points)
Any transition metal Scandium to Zinc to Lanthanum to Mercury
A Halide (or Halogen) in the fourth period _Bromine_________
Any three alkaline earth metals _Berylium to Radium________________
4
7. Define the following terms:
extensive properties
A property that depends on the amount (extent) of material
hypothesis
A guess about how a system works that will be tested.
compound
A pure material that is composed of two or more elements.
solution
A uniform or homogeneous mixture.
Kinetic Energy
Energy of a moving mass, KE=1/2 MV2
8. A tougher question, so I saved it for last.
Elemental magnesium has an atomic mass of 24.30u. There are three major
isotopes of Mg: 24Mg, 25Mg, and 26Mg. If 79% of elemental magnesium is the 24Mg isotope,
what is the % abundance of the other 2 forms?
24.30 = .79(24) + X(25) + Y(26)
1.00=.79 + X + Y
1.00-.79-X =Y
Y= .21-X
Substituting into the first equation
24.30 = .79(24) + X(25) + (.21-X)(26)
24.30 = 18.96 + 25X + (.21)26 - 26X
24.30 -18.96 -(.21)26) = 25X-26X
-.12 = -X
25
Mg = 12% abundance
26
Mg = 9% abundance