Chemistry Online

Chemistry 112 - Fall 2007 Final Exam

Multiple Choice.  There is only one correct answer for these multiple-choice questions. Answer key at bottom.

 (R = 0.08206 L atm mol^-1 K^-1;  K_w = 1.0 ´ 10^-14) 

1.   Acids in which K_a << 1 are referred to as

a) dissociators.          b) weak acids. 

c) Arrhenius acids.     d) Brønsted-Lowry acids.

e) strong acids.

2.   According to the Lewis acid-base definition, a base

a) increases the H₃O⁺ concentration in an aqueous solution.

b) increases the OH^- concentration in an aqueous solution.

c) is a proton acceptor.

d) is a proton donor.

e) is an electron-pair donor. 

3.   For the following reaction

    4 NO₂(g) 2 N₂O(g)  +  3 O₂(g)

The initial partial pressures for NO₂, N₂O and O₂ are 3.6, 5.1 and 8.0 atm, respectively.  The equilibrium pressure for NO₂ is 2.4 atm.  The equilibrium constant for this reaction is:

a) 720

b) 6.9 ´ 10² 

c) 0.0036

d) 3.6 ´ 10²

e) None of the above are correct.

4.   What is the conjugate acid of [Cr(H₂O)₆]³⁺(aq)?

a) H₃O⁺

b) [Cr(H₂O)₅OH]²⁺

c) [Cr(H₂O)₅H₃O]⁴⁺

d) [Cr(H₂O)₆]²⁺

e) [Cr(H₂O)₅]³⁺

5.   For a weak acid, the value of the pK_a added to the logarithm of the ratio of the (conjugate base) to the (conjugate acid), gives:

a) the pH 

b) [H₃O]⁺

c) the value of K_b

d) the value of K_w

e) None of these are correct.

6.   A solution is prepared by diluting 0.16 mol of HNO₃ with water to a volume of 1.0 L. What is the pH of this solution?

a) -0.80                    b) 0.80                 c) 0.796

d) 1.83                     e) 2.24

7.   What is the OH^- concentration of an aqueous solution with a pH of 10.45?

a) 3.5 ´ 10^-12 M     b) 9.4 ´ 10^-10 M     c) 1.1 ´ 10^-5 M

d) 2.8 ´ 10^-4 M  e) 7.8 ´ 10^-2 M

8.   The conjugate base of H₃O⁺  is ________.

a) OH^-                     b) H₂O                 c) OH^-

d) O^2-                       e) H^-

 

9.   For any reaction at equilibrium, the equilibrium constant for the forward reaction can be converted into the equilibrium constant for the reverse reaction by:

a) taking its reciprocal 

b) dividing K_forward by the concentrations of the products

c) taking its square root

d) multiplying by K_w

e) both constants are the same

10.  If the coefficients for the reaction shown below are all multiplied by 3, the equilibrium constant will be:

4 NO₂(g) 2 N₂O(g)  +  3 O₂(g)

a) doubled   b) raised to the ¹/₃ power    c) unchanged

d) cubed              e) None of the above.

11.  The number of hydrogen atoms in 0.050 mol of C₃H₈O₃ is: 
a.    3.0 ´ 10²² H atoms     b. 1.2 ´ 10²³ H atoms

     c.   2.4 ´ 10²³ H atoms       d.  4.8 ´ 10²³ H atoms

      e.    None of these choices is correct.

12.  Which of the statements concerning buffers is TRUE?

a) if the pH of a buffer is higher than the pK_a of the weak acid from which it is made it will have no buffering capacity.

b) buffers are resistant pH changes, even upon addition of large quantities of strong acids or bases.

c) a buffer works best when its pH is close to the pK_a of the acid from which it is made. 

d) buffers contain appreciable quantities of a strong acid and its conjugate base.

e) the pH of a buffer is concentration dependent.

                           

13.  A mixture of CO and Cl₂ has an initial partial pressures of 0.60 atm for CO and 1.10 atm for Cl₂.  After the mixture reaches equilibrium, the partial pressure of COCl₂ is 0.10 atm.  The value of K is:

CO(g)  +  Cl₂(g)COCl₂ (g)

a) 20.0         b) 470   c) 0.20

d) 0.0047     e) None of these is correct.

14.  A buffer is prepared using 10.0 mL of 1.0 M acetic acid and 10 .0 mL of 1.0 M sodium acetate;  what is the pH of this buffer? (K_a for acetic acid = 1.8 ´ 10^-5)

a)    4.744 b)  3.75     c)  9.25     d)  9.75

e)    None of the above is correct.

15.  Sulfur dioxide reacts with chlorine according to the equation shown below.

SO₂(g) + 2Cl₂(g) ® SOCl₂(g) + Cl₂O(g)

      If 0.400 mol of Cl₂ reacts with excess SO₂, how many moles of Cl₂O are formed? 
a.   0.800 mol                      b.         0.400 mol

      c.   0.200 mol                      d.          0.100 mol

      e.   0.0500 mol

 

 

16.  In the correctly balanced equation for the combustion of benzene, the coefficient for oxygen gas is:

          C₆H₆(l) + O₂(g) ® H₂O(g) + CO₂(g) 
 

      a.   9          b.  3      c.  15    d.  30

e.    None of these is correct.   

17.  For any reaction, if Q >> K:

a) more reactant will form 

b) more product will form

c) equilibrium has been reached

d) K will be greater than K_w

e) None of these.

18.  Calculate the oxidation number of the chlorine in perchloric acid, HClO₄. 

a)  -1      b)  +4      c)  +5     d)  +7 

e)   None of these is the correct oxidation number.

19.  Given a solution of 0.10 M NH₃(aq), what is the effect of adding NH₄Cl(s) to this solution?

1.   The pH will decrease.

2.   The concentration of NH₃ will increase.

3.   The concentration of H₃O⁺ will increase.

a) 1 only                  b) 2 only                  c) 3 only

       d) 1 and 3                e) 1, 2, and 3

20.  If a reaction is endothermic, cooling it will:

a) drive the reaction in the forward direction.

b) drive the reaction in the reverse direction. 

c) change the equilibrium constant

d) both a and c are correct

e) None of these are correct.

21.  Which of the following statements are true for the following equation:

                        CS₂ + 3 O₂  ®  2 SO₂ + CO₂

        a)  One mole of CS₂ will produce two moles of SO₂.

        b)  Six molecules of O₂ require three molecules of CS₂.

  c)  The reaction of one mole of O₂ will produce 2/3 mole of SO₂.

        d)  Both a and c are correct. 

        e)  All of the above are correct.

22.  The equilibrium constant for describing the solubility of a substance in two different solvents is called:

a) K_c

b) the distribution factor

c) the solubility product

d) the partition coefficient

e) None of these are correct.

23. Toluene can oxidized to benzoic acid. What is the yield of a reaction in which 1.00 kg of toluene is converted to 1.21 kg of benzoic acid?

        a)  91.2%   b)  94.8%     c  87.6%     d)  93.2%

        e)  None of the above are correct.

 

 

24.  The K_a of hypochlorous acid, HClO, is 3.5 ´ 10^-8. What [ClO^-]/[HClO] ratio is necessary to make a buffer with a pH of 7.71?

a) 2.0 ´ 10^-8             b) 0.25                    c) 0.56

d) 1.8                     e) 3.9

25.  A tightly sealed 5.0 L flask contains 781 mm Hg of Ar at 19 °C. The flask is heated until the pressure is doubled. What is the temperature of the gas?

a) -127 °C                b) 38 °C                   c) 95 °C

d) 149 °C                 e) 311 °C

26.  What is the chemical name of Cu(HSO₃)₂?

a)   Copper hydrogen sulfite

b)   Copper hydrogen sulfate

c)   Copper (I) hydrogen sulfite

d)   Copper (II) hydrogen sulfite

e)   None of the above is correct.

27.  What volume, in mL, of 0.184 M HCl will react completely with 0.395 moles of NaOH?

NaOH +  HCl ® NaCl +  H₂O

a)   2,150 mL            c)   395  mL

b)   465 mL              d)    72.7 mL

e)   You cannot answer this question without knowing the volume of the NaOH solution.

28.  A sample of a gas occupies 22.4 L at 760. mm Hg and 273 K. How many moles of the gas  are in the container?

a)   1.60 x 10^-2 b)   1.60 x 10^-4 c)   1.33 x 10^-1                            d)   1.00

e)   You cannot answer this question without knowing the molar mass of the gas.

29. In any equilibrium expression, the partial pressure of a gas can be replaced by:
a)   the molarity of the gas

b)   the molarity divided by RT

c)   the molarity multiplied by RT

d)   the molarity multiplied by nRT

e)   None of the above is correct.

30.  Which one of the following molecules or ions would be polar?

a) BF₃                      b) H₃O⁺                 c) CH₄

d) NH₄⁺                    e) CO₂

31.  In the titration of a weak acid, the equivalence point:

a) gives the [H₃O]⁺

b) gives the value of K_a

c) gives the value of K_b

d) is a function of the K_b of the conjugate base

e) None of these are correct.

32.   A sample of a gas is placed in a 2.00 L container at 300. K. The gas is now cooled to 150. K. What would the volume of the sample at this new temperature if the pressure remains constant?

a)   1.00 L   b)   4.00 L c)   1, 220 mL

d)   The volume would not change

e)  You cannot answer this question without knowing values for the initial and final pressures, P₁ & P₂.

33.  What is the correct Lewis structure for IF₃?

      a) 1             b) 2               c) 3

d) 4             e) 5

       

34. Which of the following statements concerning BH₃ are TRUE?

a) The molecular geometry of BH₃ will be trigonal planar.

b) The electron pair geometry of BH₃ will be tetrahedral.

c) BH₃ is a strong Lewis acid.

d) Answers a and c, only, are correct. 

e) All of the above are correct.

35. For the oxidation of ammonia, the reaction of 9.25 mol O₂ produced 9.60 mol H₂O.  How many moles of NO will be produced in the same reaction if we completely react 5.50 mol O₂? (4 NH3(g)  + 5 O2(g)  ® 4 NO(g)  + 6 H2O(g))
a)  4.40        b)  86.5    c)  7.40      d)  3.40      e) 3.81

36.  If the reaction quotient, Q, is greater than K_p, then

a) the chemical system has reached equilibrium.

b) the temperature must be increased for the reaction to proceed in the forward direction.

c) the reaction will proceed in the direction that results in fewer gas phase particles.

d) the reaction will proceed to the right until equilibrium is established.

e) the reaction will proceed to the left until equilibrium is established. 

37.  For most weak acids, the square root of (K_a multiplied by the concentration of the acid) gives:

a) the pH

b) [H₃O]⁺ 

c) the value of K_b

d) the value of K_w

e) None of these are correct.

 

Answer Key: 1-b, 2-e, 3-b, 4-c, 5-a, 6-b, 7-d, 8-b, 9-a, 10-d, 11-c, 12-c, 13-c, 14-a, 15-c, 16-c, 17-a, 18-d, 19-e, 20-b, 21-d, 22-d, 23-a, 24-d, 25-e, 26-d, 27-a, 28-d, 29-c, 30-b, 31-d, 32-a, 33-b, 34-d, 35-e, 36-e, 37-b