CHEM 1405
Name:_______________________________
Exam # 2 (4,5,6)
Score:
PART I – Multiple choice : (3 points each)
_____1. Compounds that have a specific number of water molecules attached to them are
A)Acids
B) Bases
C) Hydrates
D) Isotopes
_____2. How many moles are there in 68g of BI3
A) 68
B) 0.174
C) 0.314
_____3. How many grams are there in 9.00 moles of CF2Cl2
A) 363g
B) 605g
C) 1088.1g
D) 23
D) 40.3g
_____4. What are the respective stoichiometric coefficients to balance the following
equation:
C + Na2CO3 + N2  CO + NaCN
A) 1,1,1,3,2
B) 1,1,1,1,1
C) 4,1, 1, 3, 2
D) 2,1, 3,1,1
_____5. What is the balancing coefficient for oxygen when the following combustion
reaction of a hydrocarbon is balanced? C7H14 + O2  CO2 + H2O
A) 21
B) 11
C) 42
D) 10
_____6. Calculate the equivalent of 760 torrs in atm
A) 6.50
B) 760
C) 1.00
D) 65056
_____7. The pressure ______________ when the volume changes from 2.5L to 13L
A) increases
B) decreases
C) does not change D) none of these
_____8. A sample of gas has a volume of 252mL at a pressure of 641 torr. What volume,
in mL, will the gas occupy at the same temperature but at 760 torr?
A) 200
B) 299
C) 212
D) 1933
_____9. A gas fills a 2.0L balloon at a temperature of 27 ºC and a pressure of 1 atm. If
the gas in the balloon is heated to 127 ºC, what is the new volume of the balloon?
A) 2.7
B) 1.6
C) 9.5
D) 0.42
_____10. A sample of 1.5L of hydrogen gas has a temperature of 140ºC and a pressure of
0.68 atm. If the pressure changes to 1 atm and volume to 1L, what is the new
temperature?
A) 132ºC
B) 137 ºC
C) 32 ºC
D) 100 ºC
_____11. Which is the molar mass of mustard gas, C4H8Cl2S?
A) 151g
B) 76g
C) 43g
D) 159g
_____12. Which of the following states of matter undergoes a large change in volume on
heating
A) solid
B) liquid
C) gas
D) none of these
_____13. The melting point of a substance is:
A) very high for solids
B) very low for liquids
C) different from freezing
D) the same as freezing
_____14. The volume of a gas at Standard Pressure and Temperature is:
A) 22240 mL
B) 22400 mL
C) 222400 mL D) 2240 mL
_____15. Which of the following is correct at STP, pressure is:
A) at 1 pm
B) at 2 pm
C) at 1 atm
D) at 2 atm
_____16. What is the exact mass of one mole of salt with formula NaCL?
A) 59.0 g
B) 58.5 g
C) 60.0 g
D) 58.0 g
_____17. Calculate the mass in grams for a single atom of the following element: Be
A) 1.50 x 10-23 g B) 0.15 x 10-23 g C) 15.0 x 10-23 g
D) 150 x 10-23 g
_____18. Calculate the equivalent of 760 torrs in atm
A) 0.001
B) 1
C) 0.1
D) 0.01
_____19. Chlorophyll is a dark green plant pigment. Calculate the percent composition of
carbon in chlorophyll
A) 72.78%
B) 78.72%
C) 7.2785%
D) 7.872%
_____20. If iron (II) sulfide is produced from the action of heat on the following
equation:
Fe (s) + S (s)  FeS (s)
What is the correct formula for Iron (II) sulfide when the equation is balanced?
A) Fe2S
B) FeS2
C) FeS
D) Fe2S
PART II – Show your work : (8 points each)
21. A substance, NxOy, has the composition by mass 30.43% N and 69.57% O.
a)Calculate the empirical formula of this substance.
b) What is its molecular formula if its molar mass is 92 grams.?
22. Given the following equation, calculate the amount of Cu (in g) that would be
produced from 15g of Zn:
Zn(s) + CuSO4(aq)  ZnSO4(aq) + Cu(s)
23. How many grams of carbon dioxide are produced by the fermentation of 315g of
glucose (C6H12O6) according to the following equation?
C6H12O6  2C2H5OH + CO2
24. Caffeine is a naturally occurring stimulant found in tea and coffee. A sample of 138.0
g of caffeine contains 68.28g of carbon, 7.16g of hydrogen, 39.81g of nitrogen, and
22.74g of oxygen. Calculate the mass percentage of each element in caffeine.
25. Determine the number of moles of Aluminum in 113.67g of Aluminum.
BONUS QUESTION – Show all your work. (10 points)
Answer only one of the following questions:
26. What is the empirical formula of a compound containing 92.3% carbon and
7.69% hydrogen?
27. Write the chemical formula for the following ternary compounds given their
constituent ions.
(i)
Lead (II) sulfate, Pb2+ and SO42(ii)
Stannic chlorite, Sn4+ and ClO2(iii) Cobalt (II) nitrate, Co2+ and NO3(iv)
Mercurous phosphate, Hg22+ and PO43-
PART II – Show your work : (8 points each)
1.c 2.b 3.c 4.c 5.a 6.c 7.b 8.c 9.a 10.a 11.d 12.c 13.d 14.d 15.b 16.b 17.a 18.b 19.a 20.c
21.a Solving for Empirical Formula:
N: 30.43% /14 = 2.1735/2.1735 = 1, x =1
O: 69.57% /16 = 4.3481/2.1735 = 2.0005 (approximately = 2), y=2
Empirical Formula = NO2
b. Solving for Molecular Formula:
n = number of moles
n = Molecular Formula = 92 g
Empirical Formula
NO2
= 92 g
46 g
= 2
Molecular Formula = n x Empirical Formular = (NO2) n
= (NO2) 2
= N2O4
22. Zn(s) + CuSO4(aq)  ZnSO4(aq)
65.41 g of Zn Produced
1 g of Zn Produced
15 g of Zn Produced
+ Cu(s) is a Balanced Equation
63.55 g of Cu
63.55 g of Cu/65.41
63.55 g of Cu/65.41 x 15 = 14.5735 g of Cu
C6H12O6

2C2H5OH +
CO2
6(12g) + 12(1g) + 6(16g) Produced
1(12g) + 2(16g)
180 g of C6H12O6
Produced
44 g of CO2
1 g of C6H12O6
Produced
44 g of CO2 /180
315 g of C6H12O6
Produced
44 g of CO2 /180 x 315 = 77g of CO2
23.
24.
Mass percent calculation for caffeine:
C: 68.28 g/138 g x 100% = 49.5%
H: 7.16 g/138 g x 100 % = 5.0%
N: 39.81 g/138 g x 100% = 28.9%
O: 22.74 g/138 g x 100% = 16.5%
25.
Aluminum (Al) = 26.98 g by atomic mass
N ( Number of moles) in 113.67 g of Al = 113.67 g/26.98 g = 4.2131 moles (m)
BONUS QUESTION – Show all your work. (10 points)
26.
27.
See answer to problem 21a. on this test
(i) PbSO4 (ii) Sn(ClO2)2 (iii) Co(NO3)2 (iv) Hg3PO4