Chemistry 112
First Hour Exam
Name:____________
Please show all work for partial credit
1. (10 points) How many significant figures are there in the following numbers
12
.001056
___2___
__4____
12,587,000 __5____
2.01x10-3
___3___
.0100040
___6___
2. (10 points) Perform the following unit conversions:
354 :l to l
6,000 ft to mm
6.3 g/cm3 to lbs/ft3
4.88 acres to cm2 (1 acre = 43,560 ft2)
2
3. (10 points) Perform the following mathematical operations and express the result with
the correct number of significant figures:
.05 + .000458 + 100. + 24.5 = 125 (3 sig fig)
.05 x .000458 x 100. X 24.5 = .06 (1 sig fig)
(.05 + .000458) x (100. + 24.5) = 6 (1 sig fig)
4. (10 points) Name the following elements
The alkali metal in the third period ___Na___________________
Any 2 noble gases ____He, Ne, Ar, Kr, Xe, or Rn___________
A halide in the second period ____F_______________
Any transition metal __Anything from the middle of the table__
5. (10 points) How many protons, neutrons and electrons are there in each of the following
atoms or ions
# protons
# neutrons
# electrons
5
6
5
20
20
20
53
74
54
3
6. (10 points) Give the names of the following compounds
NaCl Sodium chloride
SF6 Sulfur hexafluoride
Ca(NO2)2 Calcium nitrite
H2SO4(aq) Sulfuric acid
FeCl3 Iron(III) chloride
7. (10 points) Give the molecular formula of the following compounds
Sodium oxide ___Na2O__________
Dinitrogen tetrahydride __N2H4____________
Lithium sulfate __Li2SO4______________
Hydrobromic acid __HBr(aq)_________________
Lead(IV) sulfide __PbS2________________
8. (10 points) Natural copper has an atomic mass of 63.55 amu. The two most common
isotopes of Cu are 63Cu and 65Cu. What are the relative abundances of these two isotopes
in natural copper.
4
9A (5 points) I have 10 grams of water. How many moles of water is this?
Molar mass of water = 16.00 + 2(1.008) = 18.016g
9B (5 points) I have 10 grams of water. How molecules of water is this?
0.56 moles water x 6.022×1023 molecules/mole = 3.3×1023 molecules
10. (10 points) What is the percent composition of every element in the compound
aluminum sulfate?
Aluminum sulfate = Al2(SO4)3
Molar mass
Al
2x26.98 = 53.96
S
3x32.07= 96.21
O
12x16 = 192
Total
= 342.17 g
% compositions
Al: 53.96/342.17 x 100% = 15.77% Al
S: 96.21/342.17 x 100% = 28.12% S
O: 192/342.14 x 100% = 56.11% O
Sum of %’s = 100.00%