GPC (Dunwoody, Dr. Kim's Section)                                 Calculator & Model # ____________
                                                                                        Name ________________________

Note: You must present your work for all of the questions along with a Scantron.
Make sure that you use the updated version after 10:00 AM of Friday.
The version before the time contains some inaccurate information.

R=8.3145J/(K^.mol); 1cal=4.184J; 1mi=1.609km; 1yd=0.9144m; 1gal=3.785L; 1lb=453.6g;
1atm=101,325Pa; d(water)=0.997g/mL; d(Hg)=13.6g/mL; N_A=6.022x10²³/mol; c=2.9979x10⁸m/s;
1 amu=1.66x10^-27kg; e=1.602x10^-19C; G=6.6726x10^-11Nm²/kg²; k=8.9876x10⁹J^.m/C².

1. Which salt solution is neutral ?         A(NH₄NO₃), B(KNO₃), C(Al(NO₃)₂), D(None of them).

2. pH of 0.010 M hydrochloric acid (HCl) solution is                 A(1.0), B(2.0), C(3.0), D(4.0), E(5.0).

3. pH of 0.010 M acetic acid (K_a=1.7x10^-5 for HC₂H₃O₂) is    A(2.0), B(2.9), C(3.4), D(4.3), E(4.9).

4. pH of 0.010 M sodium acetate (NaC₂H₃O₂) is                     A(6.2), B(7.8), C(8.4), D(9.2), E(10.1).

5. pH of a solution which is  0.010 M in HCl and 0.010 M in HC₂H₃O₂ is . A(1), B(2), C(3), D(4), E(5).

6. pH of a solution of 0.010 M HC₂H₃O₂ and 0.010 M NaC₂H₃O₂ is  A(3.8), B(4.8), C(5.8), D(6.8), E(7.8).

7. 10mL of 0.01M NaOH is added to 90mL of the buffer (#6), new pH be  A(3.8), B(4.8), C(5.8), D(6.8), E(7.8).

8. What is more accurate value of pH above (#7)?                  A(3.8), B(3.9), C(4.6), D(4.8), E(5.0).

9. A weak acid can act as a buffer against only (a) an acid, (b) a base; its conjugate base can act
    as a buffer against only (c) an acid, (d) a base. Therefore, a mixture of a weak acid and its conjugate
    base will resist a change in pH against both.         A(a; c), B(a; d), C(b; c), D(b; d).

10. 10mL of 0.01M NaOH is added to 90mL of water, pH must be         A(10), B(11), C(12), D(13).

11. 10mL of 0.01M NaOH is added to 90mL of 0.01 M HCl, pH be         A(1), B(2), C(3), D(4), E(5).

12. Which species has the lowest concentration in the solution in Question #5?
      A(H₂O), B(H⁺), C(OH^-), D(HC₂H₃O₂), E(C₂H₃O₂^-), F(Cl^-).

13. HCl in #5 above (a) enhances, (b) suppresses, ionization of acetic acid, therefore the degree of
      ionization of acetic acid is in #5 solution is (c) larger, (d) smaller than the one in #3 solution.
      A(a; c), B(a; d), C(b; c), D(b; d).

14. The ratio of [HCO₃^-] to [H₂CO₃] in an acid rain of pH=3.0 is
      about (A) 0.0005, (B) 0.05, (C) 2, (D) 200, (E) 2,000. (pK_a1=6.37 for H₂CO₃)

15. An acetate buffer is one of common buffers used in chemistry labs. It is needed to have a buffer pH=4.35.
      How many mL of pure acetic acid (d=1.049g/mL; K_a=1.7x10^-5) must be added to 400 mL of 0.0981M
      NaOH solution to obtain such a buffer? A(5.09), B(6.09), C(7.09), D(8.09), E(9.09) mL.

16. What is pH of a buffer prepared by mixing 50.0mL of 0.200M NH3 with 100.0mL of
    0.100M NH4Cl (Kb=1.8x10-5 for NH3)?     A(8.96), B(9.08), C(9.18), D(9.26), E(9.38).

18.  After addition of 10.0 mL.                                A(2.6), B(3.6), C(4.6), D(5.6), E(6.6).

19.   At the mid-point to the equivalence point (i.e., at 12.5mL).    A(3.6), B(4.6), C(4.8), D(5.6), E(5.8).

20.  At the equivalence point (at 25.0 mL).              A(6.7), B(7.0), C(7.7), D(8.7), E(9.7).

21.  After addition of  30.0 mL.                              A(10), B(11),   C(12),  D(13),  E(14.0).

          Sketch the titration curve (pH vs. mL) with proper label and numerical scales.

23. If [Ca⁺⁺] in a kidney is 0.0025M, at what minimum oxalate concentration do you expect
      CaC₂O₄ (K_sp=2.3x10^-9) to be precipitated to become a kidney stone?
      Ca.  A(1x10^-3), B(1x10^-6), C(1x10^-9), D(1x10^-12), E(1x10^-15) M .

24. The molar solubility (in water) of CaF₂(K_sp=3.4x10^-11) is a(2x10^-4), b(2x10^-6)M.
      Find a molar solubility of CaF₂ in a buffer solution of pH=2. c(1x10^-4), d(1x10^-3), e(1x10^-2)
      to show that calcium fluoride is more soluble in the acidic buffer solution..
      (In the acidic buffer you must consider the following equilibrium as well: H⁺+F^- = HF, K_a=6.8x10^-4).
      A(a; c), B(a; d), C(a; e), D(b; c), E(b; d), F(b; e).

25. Find the molar solubility of limestone (CaCO₃ , K_sp=3.8x10^-9) in a pure water.  a(6x10^-5), b(6x10^-7)M.
      Find a molar solubility of CaCO₃ in an acid rain  of pH=4 .   c(6x10^-5), d(1) M.
      Assume the acid rain is a buffer solution.  (K_a1=4.3x10^-7, K_a2=4.8x10^-11 for H₂CO₃ ).
      A(a; c), B(a; d), C(b; c), D(b; d).
 

27. In a presence of 1.0 M NH₃ in the water, AgCl will be (a) more, (b) less soluble, and
    a new solubility (M) of AgCl would be (c) 0.005, (d) 0.050, (e) 0.50 M. (Kf=1.7x107 for Ag(NH₃)₂⁺).
    A(a,c), B(a,d), C(a,e), D(b,c), E(b,d), F(b,e).

28. You wish to heat water to make coffee. How much heat (J) must be used to raise the temperature
      of a half gallon(1.89kg) of tap water (enough for 10 cup) from 20 to 96^oC(near the ideal brewing temperature).
     Assume that it requires 4.184 J to raise temperature of 1.00g of tap water by 1.00^oC.
     A(0.60 kJ), B(6.0 kJ), C(60 kJ), D(600kJ), E(6,000kJ).

29. 0.562g of graphite is burned in a calorimeter at 25.00^oC at 1atm to reach temperature of 25.89^oC.
      C_(graphite) + O_2(g)     ->     CO_2(g)               Heat capacity of the calorimeter is 20.7 kJ/^oC.
      Find Delta H^o_f (kJ/mol) for CO_2(g). A(0.86), B(221), C(-221), D(393), E(-393).

30. A(1x10⁶), B(2x10⁶), C(3x10⁶), D(4x10⁶) kJ of heat will be evolved when 740 kg of ammonia
      is produced at a constant pressure:     N_2(g) + 3H_2(g) -> 2NH_3(g); Delta H=-91.8 kJ

31. 33.0mL of 1.20M HCl is added to 42 mL of a solution containing excess NaOH, in a coffee-cup
      calorimeter, raising the temperature from 25.0 to 31.8^oC: HCl_(aq)+NaOH_(aq) -> NaCl_(aq)+H₂O_(l)
      Find the enthalpy (Delta H_rxn) for the neutralization rxn. Assume that the heat capacity and the density of
      the final solution are those of H₂O. A(54), B(55), C(56), D(-54), E(-55), F(-56)kJ/mol.

32. (1) Find the heat generated (-Delta H ^o_comb) when 1 mole of methane is burned;
    CH4(g)+ 2O2(g) -> CO2(g)+ 2H2O(g) knowing that DeltaH_f ^oare -74.9, -393.5 & -241.8kJ/mol
    for CH4(g), CO2(g) & H2O(g),  respectively.
   (2) Find energy required to heat 100.0gal of water from 20o to 100oC.
         If an efficiency of a burner is 50%, how many (3) mol, (4) g, and (5) L (at25^oC) of CH4 are needed?

33.  Answer Either One.

[I]   Explain the principle of the Buffering Action with an example.

[II]  Explain the Fractional Precipitation  with an example.
 

KEY to the Multiple Choice Questions