Download Practice Exam #2 with Answers

CHEMISTRY 1710 - Practice Exam #2
Section 1 - This section of the exam is multiple choice. Choose the BEST
answer from the choices which are given.
_____ 1. Which of the following solutions will have the highest concentration of chloride ions?
A. 0.20 M NaCl
C. 0.10 M AlCl3
B. 0.10 M MgCl2
D. 0.05 M CaCl2
_____ 2. How many milliliters of a 9.0 M H2SO4 solution are needed to make 0.35 L of a 3.5 M
solution?
A. 0. 14 mL
C. 140 mL
B. 0.90 mL
D. 900 mL
_____ 3. Identify HCl.
A) strong electrolyte, weak acid
C) strong electrolyte, strong acid
_____ 4. Identify NaCl.
A) weak acid
C) strong acid
B) weak electrolyte, weak acid
D) weak electrolyte, strong acid
B) weak electrolyte
D) strong electrolyte
_____ 5. Which of the following pairs of aqueous solutions will form a precipitate when mixed?
A) NH4NO3 + Li2CO3
B) Hg2(NO3)2 + LiI
C) NaCl + Li3PO4
D) AgC2H3O2 + Cu(NO3)2
_____ 6. Identify the spectator ions in the following molecular equation.
KBr(aq) + AgNO3(aq) → AgBr(s) + KNO3(aq)
A) Ag+ and BrC) K+ and Br-
B) K+ and NO3D) Ag+ and NO3-
_____ 7. Give the net ionic equation for the reaction that occurs when aqueous solutions of H2SO4
and KOH are mixed.
A) H+(aq) + OH-(aq) → H2O(l)
B) 2 K+(aq) + SO42-(aq) → K2SO4(s)
C) H+(aq) + OH-(aq) + 2 K+(aq) + SO42-(aq) → H2O(l) + K2SO4(s)
D) H22+(aq) + OH-(aq) → H2(OH)2(l)
_____ 8. The titration of 25.0 mL of an unknown concentration H2SO4 solution requires 83.6 mL of
0.12 M LiOH solution. What is the concentration of the H2SO4 solution (in M)?
A) 0.20 M
B) 0.40 M
C) 0.10 M
D) 0.36 M
_____ 9. Which of the following is an acid base reaction?
A) C(s) + O2(g) → CO2(g)
B) 2 HClO4(aq) + Ca(OH)2(aq) → 2 H2O(l) + Ca(ClO4)2(aq)
C) Fe(s) + 2 AgNO3(aq) → 2 Ag(s) + Fe(NO3)2(aq)
D) MgSO4(aq) + Ba(NO3)2(aq) → Mg(NO3)2(aq) + BaSO4(s)
_____ 10. Determine the oxidation state of Sn in Sn(SO4)2.
A) +2
B) +4
C) +6
D) 0
_____11. What element is undergoing oxidation (if any) in the following reaction?
Zn(s) + 2 AgNO3(aq) → Zn(NO3)2(aq) + 2 Ag(s)
A) Zn
B) N
C) O
D) Ag
_____12. What is the oxidation number change for the bromine atom in the following unbalanced
reduction half reaction:
BrO3- (aq) + H+ (aq) → Br- (aq) + I
A) -7
B) - 6
C) + 6
D) + 7
_____13. Which of the following signs on q and w represent a system that is doing work on the
surroundings, as well as gaining heat from the surroundings?
A) q = +, w = B) q = -, w = +
C) q = +, w = +
D) q = -, w = _____14. Calculate the change internal energy (ΔE) for a system that is giving off 45.0 kJ of heat and is
performing 855 J of work on the surroundings.
A) 44.1 kJ
B) -44.1 kJ
C) -45.9 kJ
D) 9.00 x 102 kJ
_____15. A sample of copper absorbs 43.6 kJ of heat, resulting in a temperature rise of 75.0 °C,
determine the mass (in kg) of the copper sample if the specific heat capacity of copper is 0.385 J/g°C.
A) 1.51 kg
C) 1.26 kg
B) 6.62 kg
D) 7.94 kg
_____16. The specific heat capacity of liquid water is 4.18 J/g-K. How many joules of heat are needed
to raise the temperature of 5.00 g of water from 25.1°C to 65.3°C?
A) 48.1 J
B) 840 J
3
C) 1.89 × 10 J
D) 2.08 × 10-2 J
_____17. Which of the following substances (with specific heat capacity provided) would show the
greatest temperature change upon absorbing 100.0 J of heat?
A) 10.0 g Fe, CFe = 0.449 J/g°C
B) 10.0 g H2O, CH2O = 4.18 J/g°C
C) 10.0 g ethanol, Cethanol = 2.42 J/g°C
D) 10.0 g Au, CAu = 0.128 J/g°C
_____ 18. How much energy is evolved during the reaction of 48.7 g of Al, according to the reaction
below? Assume that there is excess Fe2O3.
Fe2O3(s) + 2 Al(s) → Al2O3(s) + 2 Fe(s) ΔH°rxn = -852 kJ
A) 415 kJ
B) 769 kJ
C) 241 kJ
D) 130 kJ
_____19. Use the standard reaction enthalpies given below to determine ΔH°rxn for the
following reaction:
2 NO(g) + O2(g) → 2 NO2(g)
ΔH°rxn = ?
Given:
N2(g) + O2(g) → 2 NO(g)
ΔH°rxn = +183 kJ
1/2 N2(g) + O2(g) → NO2(g) ΔH°rxn = +33 kJ
A) -150. kJ
B) -117 kJ
C) -333 kJ
D) +115 kJ
_____20. Choose the reaction that illustrates ΔH°f for NaHCO3.
A) Na(s) + H2(g) + C(s) + O2(g) → NaHCO3 (s)
B) Na+(aq) + HCO3 -1 (aq) → NaHCO3 (s)
C) Na+(aq) + H2O (l) + CO2 (g) → NaHCO3 (s)
D) Na(s) + 1/2 H2(g) + C(s) + 3/2 O2(g) → NaHCO3 (s)
_____21. Use the information provided to determine ΔH°rxn for the following reaction:
ΔH°f (kJ/mol)
CH4(g)
CHCl3(l)
HCl(g)
CH4(g) + 3 Cl2(g) → CHCl3(l) + 3 HCl(g) ΔH°rxn = ?
-75
-134
-92
A) -151 kJ
B) -335 kJ
C) +662 kJ
D) +117 kJ
_____22. To what temperature must a balloon, initially at 25°C and 2.00 L, be heated in order to have a
volume of 6.00 L?
A) 993 K
B) 403 K
C) 75 K
D) 894 K
_____23. How many moles of CO are contained in a 5.00 L tank at 155°C and 2.80 atm?
A) 0.399 moles
B) 1.10 moles
C) 2.51 moles
D) 0.455 moles
_____24. What is the volume of 5.60 g of O2 at 7.78 atm and 415K?
A) 1.53 L
B) 565 L
C) 24.5 L
D) 0.766 L
_____ 25. Which of the following samples will have the greatest volume at STP?
A) 22 g CO
B) 22 g He
C) 22 g O2
D) 22 g Cl2
_____26. Place the following gases in order of increasing density at STP.
N2
NH3
N2O4
A) N2O4 < Ar < N2 < NH3
C) NH3 < Ar < N2 < N2O4
Ar
B) Ar < N2O4 < N2 < NH3
D) NH3 < N2 < Ar < N2O4
_____27. The density of a gas is 1.43 g/L at STP. What is the gas?
A) Cl2
B) S
C) O2
D) Ne
_____28. A 0.465 g sample of an unknown gas occupies 245 mL at 298 K and 1.22 atm. What is the
molar mass of the unknown compound?
A) 26.3 g/mol
B) 33.9 g/mol
C) 12.2 g/mol
D) 38.0 g/mol
____29. The heat of vaporization of water at 100°C is 40.66 kJ/mol. Calculate the quantity of heat that
is absorbed/released when 9.00 g of steam condenses to liquid water at 100°C.
A) 20.3 kJ of heat are absorbed.
B) 20.3 kJ of heat are released.
C) 81.3 kJ of heat are absorbed.
D) 81.3 kJ of heat are released.
_____30. Calculate the total quantity of heat required to convert 25.0 g of liquid CCl4(l) from 35.0°C to
gaseous CCl4 at 76.8°C (the normal boiling point for CCl4). The specific heat of CCl4(l) is
0.857 J/(g · °C), its heat of fusion is 3.27 kJ/mol, and its heat of vaporization is 29.82 kJ/mol.
A) 0.896 kJ
B) 1.43 kJ
C) 5.74 kJ
D) 6.28 kJ
Section 2 - Calculations Involving Chemical Equations
Consider the following reaction
BaCl2(s) + H2SO4(l)--------------> BaSO4(s) + 2 HCl (g)
A mixture of 2.65 g of BaCl2 and 6.78 g of H2SO4 are allowed to react.
Molar masses:
BaCl2 , 208.2324
H2SO4 , 98.078
BaSO4 , 233.43
HCl , 36.4606
1. How many grams of BaSO4 could theoretically be produced from the 2.65 g of BaCl2 ?
2.97
Answer:_______________g
2. How many grams of BaSO4 could theoretically be produced from 6.78 g of H2SO4 ?
16.1
Answer:_______________g
c) Which is the limiting reagent in this reaction?
BaCl
2
Answer:_______________
d) If 1.25 g of BaSO4 is actually isolated, what is the percentage yield for the reaction?
42.1%
Answer:_______________
3 - Calculations involving Solutions
1. Calculate the molarity of a solution prepared by dissolving 1.495 g of LiOH in enough water to
give a final volume of 750. mL
(Show work.)
(1.495 g LiOH) x (1 mol/23.95 g LiOH) = 0.06242 mol LiOH
(0.06242 mol LiOH)/(0.750 L) = 0.0832 M
2. Describe how you would prepare 250.0 mL of 3.000 M NaCl (M = 58.45 g/mol) from solid
NaCl.
(.2500 L soln) x (3.000 mol/1.000 L soln) x (58.45 g NaCl/1 mol NaCl) = 43.84 g NaCl
43.84 g NaCl is dissolved in enough water to make 250.0 mL.
Section 4 - Follow the directions to solve each problem.
1. An unknown liquid is vaporized in a 273-mL flask by immersion in a
water bath at 99°C. The barometric pressure is 753 torr. If the mass of the
liquid retained in the flask is 1.362 g, what is its molar mass?
a.
Find the number of moles of gas present using the ideal gas law. .009 moles
b. Using the measured mass of the liquid, find its molar mass .
150 g/mol
2. A small quantity of hydrogen was prepared by the addition of hydrochloric
acid to zinc. 195 mL of hydrogen was collected over water at 25°C and 753 torr.
from the reaction. (Pwater = 24 torr at 25°C)
a. Write the balanced chemical equation for the reaction of zinc metal with
hydrochloric acid to yield zinc chloride and hydrogen gas.
Zn (s) + 2 HCl (aq)----> ZnCl2 (aq) + H2 (g)
b. Correcting for water vapor pressure, what was the pressure of the hydrogen gas collected?
729 torr
c. Using the ideal gas equation, calculate the number of moles of hydrogen
gas collected?
.00764 moles
d. How many grams of zinc were present in the original reaction ?
.500 g