Will a precipitate of magnesium fluoride form when 300 by 1x0qI4

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									Chem 1412 Test 3 Reviews
Name: __________________________ Date: _____________


    1. Find the concentration of Pb2+ ions in a solution made by adding 5.00 g of lead(II)
       iodide to 500. mL of 0.150 M KI. [For PbI2, Ksp = 1.39  10–8.]
       A) 3.04  10–4 M
       B) 1.54  10–7 M
       C) 6.18  10–7 M
       D) 1.52  10–4 M
       E) 9.27  10–8 M


    2. Find the temperature at which Kp = 42.0 for the reaction H2(g) + I2(g)     2HI(g).
       [Given: at 25°C, for H2(g), H°f = 0, S° = 131.0 J/mol·K; for I2(g), H°f = 62.26
       kJ/mol, S° = 260.6 J/mol·K; for HI(g), H°f = 25.9 kJ/mol, S° = 206.3 J/mol·K; assume
       that H° and S° are independent of temperature.]
       A) 1040 K
       B) 168 K
       C) 539 K
       D) 1400 K
       E) 34,200 K


    3. The normal freezing point of ammonia is –78°C. Predict the signs of H, S, and G
       for ammonia when it freezes at –80°C and 1 atm: NH3(l)  NH3(s)




    4. Assuming equal concentrations of conjugate base and acid, which one of the following
       mixtures is suitable for making a buffer solution with an optimum pH of 4.6–4.8?
       A) CH3COO2Na / CH3COOH (Ka = 1.8  10–5)
       B) NH3 / NH4Cl (Ka = 5.6  10–10)
       C) NaOCl / HOCl (Ka = 3.2  10–8)
       D) NaNO2 / HNO2 (Ka = 4.5  10–4)
       E) NaCl / HCl




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5. Which species will have the greatest absolute entropy at 25°C?
   A) Ne(g)
   B) C2H2(g)
   C) H2O(l)
   D) C2H5OH(l)
   E) C4H10(g)


6. Which one of the following combinations cannot function as a buffer solution?
   A) HCN and KCN
   B) NH3 and (NH4)2SO4
   C) HNO3 and NaNO3
   D) HF and NaF
   E) HNO2 and NaNO2


7. Ozone (O3) in the atmosphere can reaction with nitric oxide (NO):
   O3(g) + NO(g)  NO2(g) + O2(g).
   Calculate the G° for this reaction at 25°C. (H° = –199 kJ/mol, S° = –4.1 J/K·mol)
   A) 1020 kJ/mol
   B) –1.22  103 kJ/mol
   C) 2.00  103 kJ/mol
   D) –1.42  103 kJ/mol
   E) –198 kJ/mol


8. For which type of titration will the pH be basic at the equivalence point?
   A) Strong acid vs. strong base.
   B) Strong acid vs. weak base.
   C) Weak acid vs. strong base.
   D) All of the above.
   E) None of the above.


9. Calculate the concentration of chloride ions in a saturated lead(II) chloride (Ksp = 2.4 
   10–4) solution.
   A) 2.4  10–4 M
   B) 4.8  10–4 M
   C) 3.9  10–2 M
   D) 1.2  10–1 M
   E) 7.8  10–2 M




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10. Which one of the following reactions would you expect to have the lowest S°?
    A) CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
    B) C2H2(g) + 5/2O2(g)  2CO2(g) + H2O(g)
    C) C2H4(g) + O2(g)  2CO2(g) + 2H2O(g)
    D) C2H6(g) + 7/2O2(g)  2CO2(g) + 3H2O(g)


11. The element oxygen was prepared by Joseph Priestley in 1774 by heating mercury(II)
    oxide:
    HgO(s)  Hg(l) + 1/2O2(g), H° = 90.84 kJ/mol.
    Estimate the temperature at which this reaction will become spontaneous under standard
    state conditions.
    S°(Hg) = 76.02 J/K·mol
    S°(O2) = 205.0 J/K·mol
    S°(HgO) = 70.29 J/K·mol
    A) 108 K
    B) 430 K
    C) 620 K
    D) 775 K
    E) 840 K


12. Will a precipitate of magnesium fluoride form when 300. mL of 1.1  10–3 M MgCl2 are
    added to 500. mL of 1.2  10–3 M NaF? [Ksp (MgF2) = 6.9  10–9]
    A) Yes, Q > Ksp
    B) No, Q < Ksp
    C) No, Q = Ksp
    D) Yes, Q < Ksp


13. Without reference to a table, arrange these reactions according to increasing S.
    1) CH4(g) + H2O(g)  CO(g) + 3H2(g)
    2) C(s) + O2(g)  CO2(g)
    3) H2O2(l)  H2O(l) + 1/2O2(g)
    A) 1 < 3 < 2
    B) 2 < 3 < 1
    C) 2 < 1 < 3
    D) 3 < 2 < 1
    E) 3 < 1 < 2




                                          Page 3
14. Calculate the equilibrium constant for the decomposition of water
    2H2O(l)        2H2(g) + O2(g)
    at 25°C, given that G°f (H2O(l)) = –237.2 kJ/mol.
    A) 0.83
    B) 6.3  10–84
    C) 2.5  10–42
    D) 1.6  1083
    E) 4.7  105


15. What volume of 0.0500 M sodium hydroxide should be added to 250. mL of 0.100 M
    HCOOH to obtain a solution with a pH of 4.50? [Ka(HCOOH) = 1.7  10–4]
    A) 540 mL
    B) 420 mL
    C) 80. mL
    D) 340 mL
    E) 500. mL


16. In which one of the following solutions will acetic acid have the greatest percent
    ionization?
    A) 0.1 M CH3COOH
    B) 0.1 M CH3COOH dissolved in 1.0 M HCl
    C) 0.1 M CH3COOH plus 0.1 M CH3COONa
    D) 0.1 M CH3COOH plus 0.2 M CH3COONa


17. A spontaneous endothermic reaction always
    A) causes the surroundings to get colder.
    B) bursts into flame.
    C) requires a spark to initiate it.
    D) releases heat to the surroundings.


18. Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of cyanic acid
    (HCNO) and 0.80 mole of sodium cyanate (NaCNO) in enough water to make 1.0 liter
    of solution.
    [Ka(HCNO) = 2.0  10–4]
    A) 0.97
    B) 3.10
    C) 4.40
    D) 3.70
    E) 4.30




                                          Page 4
19. Which of these species would you expect to have the lowest standard entropy (S°)?
    A) CH4(g)
    B) HF(g)
    C) NH3(g)
    D) H2O(g)


20. Kw for the auto-ionization of water, H2O(l)  H+(aq) + OH– (aq), is 1.0  10–14. What
    are the signs (+/–) of S° and H° for the reaction at 25°C?
    A) S° = (+) and H° = (+)
    B) S° = (+) and H° = (–)
    C) S° = (–) and H° = (+)
    D) S° = (–) and H° = (–)


21. Calculate the silver ion concentration in a saturated solution of silver(I) carbonate (Ksp =
    8.1  10–12).
    A) 5.0  10–5 M
    B) 2.5  10–4 M
    C) 1.3  10–4 M
    D) 2.0  10–4 M
    E) 8.1  10–4 M


22. 25.0 mL of a hydrofluoric acid solution of unknown concentration is titrated with 0.200
    M NaOH. After 20.0 mL of the base solution has been added, the pH in the titration
    flask is 3.00. What was the concentration of the original hydrofluoric acid solution.
    [Ka(HF) = 7.1  10–4]
    A) 0.39 M
    B) 0.27 M
    C) 0.16 M
    D) 2.4 M
    E) 0.23 M


23. In the gas phase, formic acid forms a dimmer, 2HCOOH(g)        (HCOOH)2(g). For
    this reaction, H° = –60.1 kJ/mol and G° = –13.9 kJ/mol at 25°C. Find the
    equilibrium constant (Kp) for this reaction at 75 °C.
    A) 8960
    B) 273
    C) 0.120
    D) 8.33
    E) 1.12  10–4




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24. Which of these species has the highest entropy (S°) at 25°C?
    A) CO(g)
    B) CH4(g)
    C) NaCl(s)
    D) H2O(l)
    E) Fe(s)


25. At 1500°C the equilibrium constant for the reaction CO(g) + 2H2(g)        CH3OH(g)
    has the value Kp = 1.4  10–7. Calculate G° for this reaction at 1500°C.
    A) 105 kJ/mol
    B) 1.07 kJ/mol
    C) –233 kJ/mol
    D) –105 kJ/mol
    E) 233 kJ/mol


26. Predict the normal boiling point of triethylborane (C6H15B) using the following data:

                        H°f (25°C)         G°f (25°C)
    C6H15B(l)          –194.6 kJ/mol         9.4 kJ/mol
    C6H15B(g)          –157.7 kJ/mol        16.1 kJ/mol
    A) 92°C
    B) –21°C
    C) 21°C
    D) 365°C
    E) 256°C


27. The Ksp value for lead(II) chloride is 2.4  10–4. What is the molar solubility of lead(II)
    chloride?
    A) 2.4  10–4 mol/L
    B) 6.2  10–2 mol/L
    C) 7.7  10–3 mol/L
    D) 3.9  10–2 mol/L
    E) 6.0  10–5 mol/L


28. In which one of the following solutions will acetic acid have the greatest percent
    ionization?
    A) 0.1 M CH3COOH
    B) 0.1 M CH3COOH dissolved in 0.1 M HCl
    C) 0.1 M CH3COOH dissolved in 0.2 M HCl
    D) 0.1 M CH3COOH plus 0.1 M CH3COONa
    E) 0.1 M CH3COOH plus 0.2 M CH3COONa



                                           Page 6
29. Calculate the pH of a buffer solution that contains 0.25 M benzoic acid (C6H5CO2H)
    and 0.15M sodium benzoate (C6H5COONa). [Ka = 6.5  10–5 for benzoic acid]
    A) 3.97
    B) 4.83
    C) 4.19
    D) 3.40
    E) 4.41


30. What mass of sodium fluoride must be added to 250. mL of a 0.100 M HF solution to
    give a buffer solution having a pH of 3.50? [Ka(HF) = 7.1  10–4]
    A) 0.49 g
    B) 1.5 g
    C) 3.4 g
    D) 2.3 g
    E) 0.75 g




                                        Page 7
Answer Key
   1.   C
   2.   A
   3.   E
   4.   A
   5.   E
   6.   C
   7.   E
   8.   C
   9.   E
  10.   B
  11.   E
  12.   B
  13.   B
  14.   B
  15.   B
  16.   A
  17.   A
  18.   E
  19.   B
  20.   A
  21.   B
  22.   A
  23.   D
  24.   B
  25.   E
  26.   A
  27.   D
  28.   A
  29.   A
  30.   D




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