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27 Multiple Choice Questions - Exam 3 - College Chemistry II | CHMY 143, Exams of Chemistry

Material Type: Exam; Professor: Marlow; Class: College Chemistry II; Subject: Chemistry; University: Montana State University; Term: Spring 2010;

Typology: Exams

2010/2011

Uploaded on 03/28/2011

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CHMY 143 Sโ€™10 Exam 3
1. An acid-base equilibrium system is created by dissolving 0.10 mol HF in water to a volume of 1.0 L.
What is the effect of adding 0.050 mol Fโ€“ (aq) to this solution?
a.
The pH of the solution will decrease.
b.
Some Fโ€“ reacts with H3O+, increasing the concentration of HF and reestablishing solution equilibrium.
c.
The addition of Fโ€“ will have no effect on the pH or the concentration of HF.
d.
The ionization of HF increases, increasing the concentration of Fโ€“and decreasing the pH.
e.
The ionization of HF decreases, decreasing the concentration of H3O+ and decreasing the pH.
2. What is the pH of an aqueous solution composed of 0.30 M HF and 0.10 M Fโ€“? (Ka of HF = 7.2 x 10โ€“4)
a.
0.477
b.
1.83
c.
2.67
d.
3.62
e.
6.99
3. Which of the following combinations would be best to buffer an aqueous solution at a pH of 9.0?
a.
H3PO4 and H2PO4
โ€“, Ka1 = 7.5 x 10โ€“3
b.
HNO2 and NO2
โ€“, Ka = 4.5 x 10โ€“4
c.
CH3CO2H and CH3COOโ€“, Ka = 1.8 x 10โ€“5
d.
H2PO4
โ€“ and HPO4
2โ€“, Ka2 = 6.2 x 10โ€“8
e.
NH4
+ and NH3, Ka = 5.7 x 10โ€“10
4. Each of the following mixtures can produce an effective buffer solution EXCEPT
a.
HF and NaF.
b.
Na2HPO4 and Na3PO4.
c.
NaHCO3 and Na2CO3.
d.
NaH2PO4 and Na2HPO4.
e.
HCl and KCl.
5. What is the pH of a buffer that results when 0.50 mole of H3PO4 is mixed with 0.25 mole of NaH2PO4 and
diluted with water to 1.00 L? (Acid dissociation constant of H3PO4 : Ka1 = 7.5 x 10โ€“3)
a.
1.82
b.
2.12
c.
6.91
d.
7.21
e.
12.44
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CHMY 143 Sโ€™10 Exam 3

  1. An acid-base equilibrium system is created by dissolving 0.10 mol HF in water to a volume of 1.0 L. What is the effect of adding 0.050 mol Fโ€“^ (aq) to this solution? a. The pH of the solution will decrease. b. Some Fโ€“^ reacts with H 3 O+, increasing the concentration of HF and reestablishing solution equilibrium. c. The addition of Fโ€“^ will have no effect on the pH or the concentration of HF. d. The ionization of HF increases, increasing the concentration of Fโ€“and decreasing the pH. e. The ionization of HF decreases, decreasing the concentration of H 3 O+^ and decreasing the pH.
  2. What is the pH of an aqueous solution composed of 0.30 M HF and 0.10 M Fโ€“? ( K a of HF = 7.2 x 10โ€“^4 ) a. 0. b. 1. c. 2. d. 3. e. 6.
  3. Which of the following combinations would be best to buffer an aqueous solution at a pH of 9.0? a. H 3 PO 4 and H 2 PO 4 โ€“ , K a1 = 7.5 x 10โ€“^3 b. HNO 2 and NO 2 โ€“ , K a = 4.5 x 10โ€“^4 c. CH 3 CO 2 H and CH 3 COOโ€“, K a = 1.8 x 10โ€“^5 d. H 2 PO 4 โ€“^ and HPO 42 โ€“ , K a2 = 6.2 x 10โ€“^8 e. NH 4 +^ and NH 3 , K a = 5.7 x 10โ€“^10
  4. Each of the following mixtures can produce an effective buffer solution EXCEPT a. HF and NaF. b. Na 2 HPO 4 and Na 3 PO 4. c. NaHCO 3 and Na 2 CO 3. d. NaH 2 PO 4 and Na 2 HPO 4. e. HCl and KCl.
  5. What is the pH of a buffer that results when 0.50 mole of H 3 PO 4 is mixed with 0.25 mole of NaH 2 PO 4 and diluted with water to 1.00 L? (Acid dissociation constant of H 3 PO 4 : K a1 = 7.5 x 10โ€“^3 ) a. 1. b. 2. c. 6. d. 7. e. 12.
  1. If the ratio of base to acid in a buffer increases by a factor of 10, the pH of the buffer a. increases by 1. b. decreases by 1. c. increases by 10. d. decreases by 10. e. remains unchanged.
  2. Which of the following are always true at the equivalence point of the titration of a monoprotic weak base with a strong acid? 1. The moles of acid added from the buret equals the initial moles of weak base. 2. The volume of acid added from the buret equals the volume of base titrated. 3. The pH of the solution is greater than 7.00. a. 1 only b. 2 only c. 3 only d. 1 and 3 e. 2 and 3
  3. 25.0 mL of 0.100 M CH 3 CO 2 H(aq) is titrated with 0.100 M NaOH(aq). What is the pH after the addition of 12.5 mL of NaOH? ( K a for CH 3 CO 2 H = 1.8 x 10 - 5 ) a. 3. b. 4. 74 c. 5. d. 7. e. 9.
  4. A 25.0 mL sample of 0.300 M NH 3 (aq) is titrated with 25.0 mL of 0.300 M HCl(aq). What is the pH at the equivalence point? ( K b of NH 3 = 1.8 x 10โ€“^5 ; K a of NH 4 +^ = 5.6 x 10โ€“^10 ) a. 2. b. 5. c. 7. d. 8. e. 11.2 2
  5. The solubility of AgI (s) in water is 2.16 x 10โ€“^6 g in 1.0 L at 25 ยฐC. What is the value of K sp for AgI? a. 8.5 x 10โ€“^17 b. 3.4 x 10โ€“^16 c. 4.7 x 10โ€“^12 d. 9.2 x 10โ€“^9 e. 9.6 x 10โ€“^5
  1. Which one of the following processes involves a decrease in entropy? a. the decomposition of NH 3 (g) to H 2 (g) and N 2 (g) b. the condensation of steam to liquid water c. the sublimation of CO 2 from a solid to a gas d. the evaporation of ethanol e. the dissolution of NH 4 NO 3 (s) in water
  2. All of the following statements concerning entropy are true EXCEPT a. entropy values for substances are greater than or equal to zero. b. entropy is a state function. c. a positive change in entropy denotes a change toward greater energy dispersion. d. entropy is zero for elements under standard conditions. e. the entropy of a substance in the gas phase is greater than the solid phase.
  3. Calculate the standard entropy change for the combustion of propane at 25 ยฐC. C 3 H 8 (g) + 5 O 2 (g) โˆ 3 CO 2 (g) + 4 H 2 O(g) a. โ€“ 72.9 J/K b. +72.9 J/K c. +100.5 J/K d. +877.9 J/K e. +2692 J/K
  4. For the following reaction at 298.2 K, calculate โˆ† S ยฐ(universe) given โˆ† S ยฐ(system) = โ€“ 173.1 J/K and โˆ† H ยฐ(system) = โ€“ 566.0 kJ. 2 CO(g) + O 2 (g) โˆ 2 CO 2 (g) a. โ€“ 2071.3 J/K b. โ€“ 739.0 J/K c. โ€“ 175.0 J/K d. โ€“ 171.3 J/K e. +1725.0 J/K
  5. When a real gas expands from high pressure to a lower pressure, its temperature decreases. What are the signs of โˆ† H and โˆ† S? a. โˆ† H < 0 and โˆ† S < 0 b. โˆ† H < 0 and โˆ† S > 0 c. โˆ† H > 0 and โˆ† S < 0 d. โˆ† H > 0 and โˆ† S > 0 e. โˆ† H < 0 and โˆ† S = 0 Species S ยฐ (J/K mol) C 3 H 8 (g) 270. O 2 (g) 205. CO 2 (g) 213. H 2 O(g) 18 8.
  1. If โˆ† G ยฐ < 0 for a reaction at all temperatures, then โˆ† H ยฐ is ____ and โˆ† S ยฐ is ____. a. negative, positive b. positive, negative c. negative, negative d. positive, positive e. positive, either positive or negative
  2. Diluting concentrated sulfuric acid with water can be dangerous. The temperature of the solution increases rapidly. What are the signs of โˆ† H , โˆ† S , and โˆ† G for this process? a. โˆ† H < 0, โˆ† S > 0, โˆ† G < 0 b. โˆ† H < 0, โˆ† S < 0, โˆ† G < 0 c. โˆ† H < 0, โˆ† S > 0, โˆ† G > 0 d. โˆ† H > 0, โˆ† S > 0, โˆ† G < 0 e. โˆ† H > 0, โˆ† S < 0, โˆ† G > 0
  3. At what temperatures will a reaction be product favored if โˆ† H ยฐ = +45 kJ/mol and โˆ† S ยฐ = +312 J/K mol? a. All temperatures below 144 K. b. All temperatures above 144 K. c. Temperatures between 45 K and 312 K. d. The reaction will be spontaneous at any temperature. e. The reaction will never be spontaneous.
  4. Calculate โˆ† G ยฐ for the reaction below at 25.0 ยฐC, given โˆ† H ยฐ = โ€“ 231.1 kJ/mol and โˆ† S ยฐ = โ€“ 287.6 J/K mol. CS 2 (g) + 3 Cl 2 (g) โˆ S 2 Cl 2 (g) + CCl 4 (g) a. โ€“ 518.7 kJ b. โ€“ 316.9 kJ c. โ€“ 145.3 kJ d. โ€“ 56.5 kJ e. +56.5 kJ
  5. โˆ† G ยฐ for the following reaction is โ€“ 140.8 kJ. Given that โˆ† Gf ยฐ C 2 H 2 (g) = +209.2 kJ/mol, calculate the free energy of formation, โˆ† Gf ยฐ of C 2 H 4 (g). C 2 H 2 (g) + H 2 (g) โˆ C 2 H 4 (g) a. โ€“ 350.0 kJ/mol b. โ€“ 68.4 kJ/mol c. โ€“ 1.486 kJ/mol d. +34.2 kJ/mol e. +68.4 kJ/mol