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Chemistry 105A Exam I September 28, 2007
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Multiple choice (20 questions, 3 pts. each) Darken the correct answer on the answer sheet. Remember
there are also 3 problems given after the multiple choice questions. Budget your time accordingly.
- Which one of the following is a chemical process?
a) dissolving sugar in water
b) the condensation of water vapor
c) crushing of stone
d) the explosion of nitroglycerine
e) melting of ice
- Of the following, only ____________ is an extensive property.
a) temperature b) density
c) boiling point d) freezing point
e) mass
- How many significant figures should there be in the answer to the following problem?
a) 4 b) 3 c) 2 d) 1
- There are ___________ pg in a g.
a) 10
6
b) 1000 c) 100 d) 0.
- Iron has a density of 7.87 g/cm
3
. What is the mass (in grams) of an iron bead with a radius of 2.5 mm?
(V
sphere
= 4r
3
a) 5.5 g b) 32.97 g c) 0.52 g d) 120.25 g
- Which experimental evidence led to the proposal of a nuclear model of the atom?
a) The cathode ray tube
b) The gold foil experiment
c) The oil-drop experiment
d) The discovery of radioactivity
75
89 30. 46
- The empirical formula of a compound made up of molecules containing 8 carbon atoms, 8 hydrogen
atoms, and 4 oxygen atoms is
a) C 8
H
8
O
4
b) CHO
c) C 4
H
4
O
2
d) C 2
H
2
O
- Use the following information to identify the atom or ion.
Mass number Protons Neutrons Electrons
a) Co
3+
b) Al
3+
c) Al d) Co
- Which group of elements is most likely to form ions by gaining two electrons?
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac
a) b) c) d) e)
- Bromite ion is
a) BrO
b) BrO 2
c) BrO 3
d) BrO 4
- The coefficients required to correctly balance the reaction below are
Ba(OH) 2
(s) + H 3
PO
4
(aq) Ba 3
(PO
4
2
(s) + H 2
O(l)
a) 4,6,3,2 b) 2,3,1,
c) 1,1,1,1 d) 3,2,1,
e) none of these
- The mass percentage of H in CH 4
O is
a) 12.5% b) 4.032% c) 37.5% d) 50.0% e) 25.13%
- Based on the equations below, which metal is the most active?
Pb(NO 3
2
(aq) + Fe(s) Fe(NO 3
2
(aq) + Pb(s)
Cu(NO 3
2
(aq) + Ag(s) No reaction
Cu(NO 3
2
(aq) + Pb(s) Pb(NO 3
2
(aq) + Cu(s)
a) Pb b) Fe c) Cu d) Ag
TO RECEIVE FULL CREDIT, YOU MUST SHOW YOUR WORK ON THE ANSWER SHEET
FOR THE FOLLOWING PROBLEMS!
- (10 pts) A compound with a molecular weight of 110.1 g/mol that contained only C, H, and O was
analyzed by combustion. The combustion of a 5.19 g sample resulted in the formation of 12.4 g of
CO
2
and 2.55 g of H 2
O. What is the molecular formula of this compound?
- (12 pts) A 35.6 mL sample of Ba(OH) 2
required 65.7 mL of 0.127 M HCl to neutralize it. a) Give the
balanced equation. b) Calculate the concentration of barium hydroxide.
- (18 pts) In the reaction below, 8.46 kg of Mg 3
N
2
is reacted with water to produce ammonia and MgO.
a) How many kg of H 2
O are needed to react with the given amount of Mg 3
N
2
? b) What is the
theoretical yield of MgO in this reaction? c) Given an actual yield of 8.65 kg of MgO, determine the
percent yield of the reaction.
Mg 3
N
2
+ 3H
2
O 2NH
3
ANSWER KEY
Chemistry 105 Exam I September 28, 2007
1. D 2. E
3. B 4. A
5. C 6. B
7. D 8. B
9. D 10. B
11. D 12. A
13. B 14. C
15. A 16. B
17. C 18. A
19. D 20. B
- (10 pts) A compound with a molecular weight of 110.1 g/mol that contained only C, H, and O was
analyzed by combustion. The combustion of a 5.19 g sample resulted in the formation of 12.4 g of
CO
2
and 2.55 g of H 2
O. What is the molecular formula of this compound?
2
2
2 2
2
2
2 2
1 mole CO 1 mole C 12 g C
12.4 g CO × 3.38 g C
44 g CO 1 mole CO 1 mole C
1 mole H O 2 mole H 1 g
2.55 g H O 0.28 g H
18 g H O 1 mole H O 1 mole H
5.19 g - (3.38 g C + 0.28 g H) = 1.53 g O
1mole
3.38 g C
g
3 3 mole
C 0.28 mole
0.28 mole C 2.93 3
12 g C 0.10 mole
1 mole H 0.28 mole
0.28 g H 0.28 mole H 2.93 3
1 g H 0.10 mole
1 mole O 0.10 mole
1.53 g O 0.10 mole O 1
16 g O 0.10 mole
Empirical formula: C H O FW=
g
mole
g
mole
6 6 2
MW
FW
Molecular formula: C H O
