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?
.480020
___6___
480020 ___5___
.048002x10-5 __5_____
.
1B. Below are the answers to different calculations. Express this number with the correct
number of significant figures
67 x 1001 = 67067 _67000____
13 + 67 = 80 __80.________ Decimal shows good to the 1's place
(67x1001)/(13+67) = 838.3375
2. Perform the following unit conversions:
786 ìs to cs
786 footAlbs to cmAkg
786 lbsAin-2 to kgAm-2
840_______
2
3. Calculate the Molecular mass of the following compounds
SnCl4
118.7 + 4(35.45) = 260.5u
(NH4)2SO4
2(14.01)+8(1.008) + 32.07 + 4(16.00) = 132.154u
Magnesium sulfide (If you don’t know the formula, make one up for partial credit)
MgS 24.31+32.07 = 56.38u
Bromine pentafluoride
(If you don’t know the formula, make one up for partial credit)
BrF5 79.90+5(19.00) = 174.9u
4. Complete the following table:
Complete Symbol
# protons
# electrons
# neutrons
21
21
24
17
17
18
25
18
29
34
36
45
Note: On the original test I reversed the positions of the atomic number and mass number
on the first element, Scandium. I did not take off points for the people who followed my
incorrect lead. But one person did correct me and I gave that person a bonus point!
3
5. Balance the following chemical reactions:
Na(s) + F2(g) 6NaF(s)
2Na(s) + F2(g) 62NaF(s)
Ca3N2(s) + HI(g) 6CaI2(s) + NH3(g)
Ca3N2(s) + 6HI(g) 63CaI2(s) + 2NH3(g)
C3H6(l) + O2(g) 6 CO2(g) + H2O(g)
2C3H6(l) +9 O2(g) 6 6CO2(g) + 6H2O(g)
6A. In the blank periodic table below please indicate where the following things are found:
Inner transition metals
XXX
Alkaline earth metals
YYYY
Third 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 Halide _Fluorine to Astatine__________
An alkaline earth metal in the second period __Berylium______________
Any three inert gases _Helium to Radon________________
4
7. Define the following terms:
Potential Energy
Energy associated with the position of an object in a force field.
Element
A pure substance that contains only one type of atom.
Heterogeneous mixture
A mixture of material in which different components can be seen.
Solution
A homogenous mixture or the combination of solvent and solute.
Accuracy
How close your answers are to the true value.
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 76% of elemental magnesium is the 24Mg isotope,
what is the % abundance of the other 2 forms?
24.30 = .76(24) + X(25) + Y(26)
1.00=.76 + X + Y
1.00-.76-X =Y
Y= .24-X
Substituting into the first equation
24.30 = .76(24) + X(25) + (.24-X)(26)
24.30 = 18.24 + 25X + (.24)26 - 26X
24.30 -18.24 -(.24)26) = 25X-26X
-.18 = -X
25
Mg = 18% abundance
26
Mg = 6% abundance