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?
6060
___3___
.6060 ___4____
.06060x105 __4_____
1B. Below are the answers to different calculations. Express this number with the correct
number of significant figures
13 x .651 = 8.463
___8.5_______
13 + 67 = 80 __80.________
(13 and 67 are good to the 1's place)
(13+67) /(13 x .651) = 9.4529
__9.5________
2. Perform the following unit conversions:
34 Gg to mg
34 footAlbs to cmAkg
41 lbsAin-2 to kgAm-2
2
3. Calculate the Molecular mass of the following compounds
FeCl3
55.85 + 3(35.45) = 167.2u
Mg(NO3)2
24.31 + 2(14.01) + 6(16.00 = 148.33u
Lithium fluoride (If you don’t know the formula, make one up for partial credit)
LiF = 6.941 + 19.00 =25.941u
Sulfur trioxide (If you don’t know the formula, make one up for partial credit)
SO3 = 32.07 + 3(16.00) = 80.07u
4. Complete the following table:
Complete Symbol
# protons
# electrons
# neutrons
15
15
16
14
14
14
25
22
29
8
10
8
3
5. Balance the following chemical reactions:
Mg(s) + O2(g) 6MgO(s)
2Mg(s) + O2(g) 62MgO(s)
Ca3N2(s) + HF(g) 6CaF2(s) + NH3(g)
Ca3N2(s) + 6HF(g) 63CaF2(s) + 2NH3(g)
C6H6(l) + O2(g) 6 CO2(g) + H2O(g)
2C6H6(l) + 15O2(g) 6 12CO2(g) + 6H2O(g)
6A. In the blank periodic table below please indicate where the following things are found:
Halides XXX
Lanthanides YYYY
Fifth 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 alkaline earth metal __Beryllium to Radium_______________
A noble gas in the second period _Neon_______________
Any three alkali metals ___Lithium to Francium______________
4
7. Define the following terms:
Intensive properties
Properties like density that do not depend on the amount of material.
Accuracy
How close your values are to the true value.
Diatomic
A molecule that contains 2 atoms
solvent
The medium into which a solute will be dispersed.
Potential Energy
Energy associated with the position of an object in a force field.
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 78% of elemental magnesium is the 24Mg isotope,
what is the % abundance of the other 2 forms?
24.30 = .78(24) + X(25) + Y(26)
1.00=.78 + X + Y
1.00-.78-X =Y
Y= .22-X
Substituting into the first equation
24.30 = .78(24) + X(25) + (.22-X)(26)
24.30 = 18.72 + 25X + (.22)26 - 26X
24.30 -18.72 -(.22)26) = 25X-26X
-.14 = -X
25
Mg = 14% abundance
26
Mg = 8% abundance