KEY EXAM 2
NAME_____KEY-Answers highlighted______(1 pt.)
CHEM 1211 VSU
100 points total (Multiple choice, 3 points each)
Dr. Gosnell
October 3, 2005
1. Ammonia is prepared by reacting nitrogen and hydrogen gases at high temperature according to the
unbalanced chemical equation below. What are the respective coefficients when the equation is balanced
with the smallest whole numbers?
__ N2(g) + __ H2(g) → __ NH3(g)
a) 1, 1, 1
b) 1, 3, 1
c) 1, 3, 2
d) 2, 1, 2
e) 2, 3, 2
2. The reaction of calcium with elemental chlorine yields calcium chloride. Which is a balanced chemical
equation for this reaction?
a) Ca(s) + Cl2(g) → CaCl(s) + Cl(g)
c) Ca(s) + 2 Cl2(g) → CaCl4(s)
b) Ca(s) + Cl2(g) → CaCl2(s)
d) 2 Ca(s) + Cl2(g) → 2 CaCl(s)
3. Which is a balanced chemical equation for the combustion of pentane, C5H12?
a) C5H12(g) + 8 O2(g) → 5 CO2(g) + 6 H2O(g)
c) C5H12(g) + 9 O2(g) → 4 CO2(g) + 5 H2O(g)
b) C5H12(g) → 5 C(s) + 6 H2(g)
d) C5H12(g) + 11 O2(g) → C5O10(g) + 6 H2O(g)
4. How many moles of Al2O3 are formed from the reaction shown if 5.0 moles of Al react with excess O2?
4 Al(s) + 3 O2(g) → 2 Al2O3(s)
 2molAl 2 O3 
5.0molAl
  2.5molAl 2 O3
 4molAl 
a) 1.0 mol
b) 2.0 mol
c) 2.5 mol
d) 5.0 mol
e) 10.0 mol
5. Copper reacts with nitric acid to produce copper(II) nitrate, nitrogen dioxide gas, and water. If you have
0.500 moles of Cu, ________.
Cu(s) + 4 HNO3(aq) → Cu(NO3)2(aq) + 2 NO2(g) + 2 H2O()
a) you need at least 0.125 moles of HNO3 to produce 0.500 moles of Cu(NO3)2.
b) you need at least 0.250 moles of HNO3 to produce 0.500 moles of Cu(NO3)2.
c) you need at least 2.00 moles of HNO3 to produce 0.500 moles of Cu(NO3)2.
d) you need at least 2.00 moles of HNO3 to produce 1.00 moles of Cu(NO3)2.
e) you need at least 2.00 moles of HNO3 to produce 2.00 moles of Cu(NO3)2.
6. Dinitrogen trioxide, a blue solid, dissociates to form nitrogen monoxide and nitrogen dioxide gases. What
mass of nitrogen dioxide is formed from the decomposition of 13.1 g of N2O3?
N2O3 → NO + NO2 (balanced reaction)
 1molN 2 O3  1molNO2  46.0055gNO2 


  7.93gNO2
13.1gN 2 O3 
76
.
0116
gN
O
1
molN
O
1
molNO
2 3 
2 3 
2


a) 5.17 g
b) 7.93 g
c) 6.55 g
d) 12.8 g
e) 21.6 g
7. How many moles of Fe2O3(s) can be produced from the reaction of 0.45 mol Fe(s) with 0.30 mol O2(g)?
4 Fe(s) + 3 O2 → 2 Fe2O3(s) (balanced)
Notice the Fe(s) is in excess for amount of O2 given, so O2 is
the limiting reagent. Use it to find moles of product.
 2molFe2 O3 
  0.20molFe2 O3
0.30molO2 
 3molO2 
a) 0.15 mol
b) 0.20 mol
c) 0.23 mol
d) 0.45 mol
e) 0.75 mol
8. The numbers preceding the formulas in chemical equations are referred to as the ________ coefficients.
a) theoretical
b) molar
c) equality
d) stoichiometric
e) formula
9. The ______ yield is the maximum amount of a product that can be produced from a reaction.
a) percent
b) actual
c) theoretical
d) saturation
e) ultimate
10. Which is/are the reason(s) that chemical reactions must be balanced?
a) Law of conservation of mass and matter.
c) Law of constant composition
e) all of the above
b) Law of conservation of energy
d) Law of definite composition.
11. What is a correct method for determining how many grams of calcium oxide are produced in the reaction
of 10.0 g calcium with excess oxygen?
2 Ca(s) + O2(g) → 2 CaO(s)
 40.08 mol Ca   2 mol CaO 
1 g CaO

a) 10.0 g Ca 


=
1.00 g

  2 mol Ca  56.08 mol CaO 
 40.08 mol Ca   1 mol CaO 
1 g CaO

b) 10.0 g Ca 


=
1.00 g

  2 mol Ca  56.08 mol CaO 
 1 g Ca  2 mol CaO  56.08 g CaO 
c) 10.0 g Ca 


=
 40.08 mol  1 mol Ca  1 mol CaO 
 1 mol Ca   1 mol CaO  56.08 g CaO 
d) 10.0 g Ca 


=
 40.08 g   2 mol Ca  1 mol CaO 
 1 mol Ca   2 mol CaO  56.08 g CaO 
e) 10.0 g Ca 


=
 40.08 g   2 mol Ca  1 mol CaO 
12. What is the percent yield for the reaction shown if 1 mole of O2 produces 9.0 grams of water?
2 H2 + O2 → 2 H2O
1 mole of O2 can at most produce 2 moles of water (theoretical yield is 36 g since molar mass of water is
about 18 g/mol. So %yield = (9g/36g)x100=25%
a) 400%
b) 100%
c) 50%
d) 25%
e) not enough information given
13. A 4.236 g sample of CxHy is combusted to give 3.810 g of H2O and 13.96 g of CO2. What is the
empirical formula of the compound?
 1mol 
  .212mol
molH 2 O  3.810 g 
 18.0089 g 
 1mol 
  0.317mol
molCO2  13.96 g 
 44.0098 g 
All the hydrogen goes into the water……have 0.414mol of H (2 H atoms per water molecule).
All the C goes into the carbon dioxide…..have 0.317 mol C
Find the right ratio of H:C that equals 0.414/0.317=1.31
a) C2H3
b) C3H2
c) C3H4
d) C4H3
e) C5H12
14. If 2.0 g of H2 are mixed with 30.0 g of O2, there are ______ grams of _____ in excess.
2 H2 + O2 → 2 H2O
 1mol 
  1molH 2
molH 2  2.0 g 
 2g 
 1mol 
  0.937molO2
molO2  30 g 
 32 g 
You need 2 moles of hydrogen for every one mole of oxygen…you don’t have that much, so hydrogen is the
limiting reagent. One mole of hydrogen will react with 0.5 mol of oxygen, so you’ll have
(0.937mol-0.5mol)(32g/1mol)=14 g of oxygen left over
a) 0.5……H2
b) 29.0……O2
c) 14.0……O2
d) 1.0……O2
15. If reactants A and B are mixed and all of A is consumed and some B is left over, then A is the ____.
a) theoretical reactant
b) stoichiometric reactant
c) % yield reactant
d) limiting reactant
16. Which scientist discovered the principles underlying the need for balancing reactions?
a) Antoine Lavoisier
b) Marie Curie
c) Ernest Rutherford
d) Isaac Newton
17. If 23 g of Na are reacted completely with 18 g of water, how many total grams of products are
produced?
2 Na + 2 H2O → 2 NaOH + H2
Use Law of conservation of mass. Exactly stoichiometric amounts are reacted together so product mass
equals reactant mass.
a) 23 g
b) 5 g
c) 41 g
d) not enough information given
18. Which one of the following compounds is a weak electrolyte when dissolved in water?
a) sodium hydroxide (NaOH)
c) acetic acid (CH3CO2H)
b) sodium acetate (NaCH3CO2)
d) sucrose (C12H22O11)
19. If 0.10 mole of each of the following compounds is dissolved to a volume of 1.0 L in water, which one
will have the highest concentration of dissolved ions?
a) HF
b) NaOH
c) MgSO4
d) Al(NO3)3
e) CaI2
20. Fish consume O2 that is dissolved in water through their gills. In water O2 is ____________.
a) miscible
b) decomposed to O atoms
c) a solute
d) a weak electrolyte
21. If 2.891 g MgCl2 is dissolved in enough water to make 500.0 mL of solution, what is the molarity of the
magnesium chloride solution?
 1molMgCl 2
2.891g 
 molesMgCl 2 
 95.211gMgCl 2
M 

Liters
0.500 L


a) 5.782 × 10-3 M


  0.006073M
b) 1.518 × 10-2 M
c) 6.073 × 10-2 M
d) 0.5505 M
22. How many liters of 0.1107 M KCl(aq) contain 15.00 g of KCl?
 1molKCl 
0.201molKCl
molKCl  15.00 g 
 74.5513gKCl 
a) 0.02227 L
b) 0.5502 L
volume 
c) 1.661 L
molKCl 0.201mol

 1.818L
Molarity 0.1107 M
d) 1.818 L
e) 123.8 L
23. How many mL of a 0.5 M stock solution of NaCl is needed to make 100 mL of a 0.10 M NaCl?
0.100L 0.10M   0.02 L  20mL
C1V1 =C2V2 Solve for V1
a) 20 mL
b) 80 mL
0.5M
c) 5 mL
d) 0.050 mL
24. The piece of glassware shown is called a/an __________ flask.
a) Erlenmeyer
b) volumetric
c) graduated
d) dilution
25. Which of the following statements concerning electrolytes are correct?
1. All ionic compounds are strong electrolytes. (some are insoluble, so this is false)
2. Weak acids, such as acetic acid, are weak electrolytes.
3. Molecular species are weak electrolytes, provided they dissolve in water. (some are
nonelectrolytes)
a) 1 only
b) 2 only
c) 3 only
d) 1, 2, and 3
26. What ions are produced from dissolving sodium hydroxide in water?
a) Na+ and H+
b) Na- and H+
c) Na+ and OH-
d) Na+ and O2-
27. Which are not solutions?
a) air
b) the alloy brass (contains copper and zinc)
c) sweet tea
All shown are solutions
28. A solution where water is the solvent is __________________.
a) aqueous
b) hydrating
c) miscible
d) saturated
29. If 100 g of substance X is mixed with 1 L of water and some, but not all, of X dissolves, the resulting
solution is ____.
a) unsaturated
b) saturated
c) supersaturated
d) a weak electrolyte
30. If a solid forms when two liquid reactants are mixed, the reaction can be classified as a/an ____ reaction.
a) exchange b) acid-base
c) oxidation-reduction
d) precipitation
31. How would you classify the following reaction?
CuSO4 (aq) + Zn (s) → ZnSO4 (aq) + Cu (s)
a) single displacement
b) double displacement
c) acid-base
d) insoluble
32. Which is the definition of molarity?
a) grams of solute dissolved per liter of solvent
c) moles of solute dissolved per liter of solvent
b) grams of solute dissolved per 100 grams solvent
d) moles of solute dissolved per liter of solution
33. If water is heated what happens to the solubility of most substances?
a)
b)
c)
d)
The solubility of solids increases, but the solubility of gases decreases.
The solubility of solids decreases, but the solubility of gases increases.
Solids and gases become more soluble.
The solubility is not affected by temperature.
Bonus Questions (3 pts. each)
34. What mass of carbon reacts completely with 17.8 grams of SiO2 according to the following equation?
SiO2(s) + 3 C(s) → SiC(s) + 2 CO(g)
 1molSiO2  3molC  12.011gC 


17.8gSiO2 
  10.7 gC
60
.
0843
gSiO
1
molSiO
2 
2  1molC 

a) 1.19 g
b) 3.56 g
c) 7.12 g
d) 10.7 g
e) 53.4 g
35. When 1.500 g of a metal oxide is heated, the compound decomposes in the reaction shown below. If
0.1035 g O2 is produced, what is the identity of the metal?
2 M2O(s) → 4 M(s) + O2(g)
 1molO2 
  .00323molO2
molO2  0.1035 g 
 31.9988 gO2 
You produce 4 times the moles of metal = 0.00323 x 4=0.0129 mol
The mass of metal is the original reactant mass minus the mass of oxygen = 1.500g – 0.1035g =1.3965g
Molar mass is grams/mol
1.3965 g
 108.2 g / mol
0.0129mol
So it must be Ag (silver), see the
periodic table.
a) Ag
b) Hg
c) In
d) K
e) Na