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?
.45050
___5____
45050 ____4___
.04505x10-3 __4_____
1B. Below are the answers to different calculations. Express this number with the correct
number of significant figures
67 x 1001 = 67067 __67000_____
67 + 33 = 100
_100._________ decimal shows good to the 1's place
(67x1001)/(67+33) = 670.67
2. Perform the following unit conversions:
87 cm to Mm
87 footAlbs to cmAkg
87 lbsAin-2 to kgAm-2
_670_________
2
3. Calculate the Molecular mass of the following compounds
N2O
2(14.01) + 16.00 = 44.02u
Mg(NO2)2
24.31 + 2(14.01) + 4(16.00) = 116.33u
Calcium oxide (If you don’t know the formula, make one up for partial credit)
CaO 40.08 + 16.00 = 56.08
Phosphorous pentachloride
(If you don’t know the formula, make one up for partial credit)
PCl5 30.97 + 5(34.45) = 208.22u
4. Complete the following table:
Complete Symbol
# protons
# electrons
# neutrons
29
29
34
15
15
16
25
21
30
16
18
16
3
5. Balance the following chemical reactions:
Li(s) + Cl2(g) 6LiCl(s)
2Li(s) + Cl2(g) 62LiCl(s)
Mg3N2(s) + HBr(g) 6MgBr2(s) + NH3(g)
Mg3N2(s) + 6HBr(g) 63MgBr2(s) + 2NH3(g)
C2H2(l) + O2(g) 6 CO2(g) + H2O(g)
2C2H2(l) + 5O2(g) 6 4CO2(g) + 2H2O(g)
6A. In the blank periodic table below please indicate where the following things are found:
Alkaline earth metals XXX
ActinidesYYY
Second period elementsZZZ
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 Noble gas Helium to Radon_________________
A halide in the second period Neon________________
Any three transition metals _Scandium to Zinc to Lanthanum to Mercury_______
4
7. Define the following terms:
Kinetic Energy
Energy associated with a moving mass = ½ MV2
Precision
How close your values are to each other.
Homogeneous mixture
A mixture that is so uniform you cannot see and individual component
Also a solution.
Solute
A material that is going to be dispersed in a solvent
Hypothesis
A guess about how a system works that will be tested.
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: 24 Mg, 25 Mg, and 26 Mg. If 77% of elemental magnesium is the 24Mg isotope,
what is the % abundance of the other 2 forms?
24.30 = .77(24) + X(25) + Y(26)
1.00=.77 + X + Y
1.00-.77-X =Y
Y= .23-X
Substituting into the first equation
24.30 = .77(24) + X(25) + (.23-X)(26)
24.30 = 18.48 + 25X + (.23)26 - 26X
24.30 -18.48 -(.23)26) = 25X-26X
-.16 = -X
25
Mg = 16% abundance
26
Mg = 7% abundance