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Chemistry 112
First Hour Exam
Name:____________
Please show all work for partial credit
1. (10 points) Covert the following weights to grams
A. 1 kg
1kg × (1000 g/1 kg) = 1000 g
B. 1 :g
1:g × (1x10-6 g/1:g)=1x10-6 g
C. 1 mg
1mg × (1x10-3 g/1mg) = 1x10-3 g
D. 1 lb.
1 lbs × (453.59 g/1lbs) = 453.59 g
2. (8 points) How many significant figures should you have in the answer to the following
problems?
A. 1.05/.004 __1_________
B. 0.0035-0.0005 __2______
C. 1.0397-0.0002 ___5______
D. (1.345+2.457)/2 __1______
3. (5 points) What is the difference between a homogeneous mixture and a heterogeneous
mixture?
A heterogeneous mixture has visibly distinguishable parts, while the parts of a
homogeneous mixture cannot be seen by eye.
4. (5 points) What is the difference between an element and a compound?
A compound is a substance with a constant composition that can be broken down to
elements by chemical processes. Elements cannot be broken down by chemical means.
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5. (5 points) Based on the atomic mass of 12C, calculate the mass of a proton or a neutron
(You may assume they have the same mass)
1 mole C ×
12 g
1 atom
mole
×
×
=
23
mole 6.02 x10 atoms 12 protons and neutrons
1.66x10-24 g
6. (8 points) What is the name of the element with an atomic number of 20? Calcium
Is this element a metal or a non-metal? metal
What family of elements is this element in? Alkaline Earth
What period of elements is this element in? 4th
7. (8 points) What is the name of the element that is the second period of the periodic table
and is a halide? Fluorine
Is this element a metal or a non-metal? Non-metal
What is the atomic number of this element? 9
How many neutrons does the nucleus of this element contain? 10
8. (12 points) Give the chemical formula for the following compounds.
Sodium chloride NaCl
Lithium nitride Li3N
Iron(II) oxide FeO
Potassium sulfate K2SO4
Sulfur hexafloride SF6
Sulfuric acid H2SO4
9. (12 points) Give names of the following compounds.
CO2 Carbon dioxide
Fe2O3 Iron(III) oxide
BaCl2 Barium Chloride
HNO3(aq) Nitric Acid
K2PO4 Potassium phosphate
AgCl Silver chloride
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10. (10 points) What is the percent composition of elements in the ethyl alcohol (C 2H6O)?
Mass C = 12.0 1 × 2
=24.02
Mass O = 16.00 × 1 =16.00
Mass H = 1.008 × 6 =6.048
Total
=46.068
% C = 24.02/46.068 × 100%
% O = 16.00/46.068 × 100%
% H = 6.048/46.068 × 100%
= 52.14 %
= 34.73 %
= 13.13 %
11. ( 5 points) After this test you might go out and have a beer or two. If you consume 1 g
of ethyl alcohol while drinking this beer, how many molecules of alcohol have you imbibed?
1 mole
6.022 x10 23 molecules
1g×
×
= 1307
.
x10 23 molecules
46.048 g
1 mole
12. (12 points) Saturday morning you might need a little caffeine to recover from a late
night of partying. Caffeine is 49.48% C, 5.15 % H, 28.87% N and 16.49% O. It also has a
molar mass of 194.2 g/mol. What is the molecular formula of caffeine?
194.2 g caffeine/mol
194.2 g caffeine/mol
194.2 g caffeine/mol
194.2 g caffeine/mol
×.4948 C/caffeine = 96.09 g C
×.0515 H/caffeine = 10.00 g H
×.2887 N/caffeine = 56.07 mole N
×.1649 O/caffeine = 32.02 mole O
96.09g C × 1 moleC/12.01g C =8 mole C
10.00 g H × 1 moleH/1.008g H =10 mole H
56.07 mole N × 1 moleN/14.01 g N =4 mole N
32.02 mole O × 1 moleO/16.00g O =2 mole O
C8H10N4O2