Chem 106 ConcepTests

Spring, 2000

44. The oxidation number for carbon in CO₂ is

a. -4

b. -2

c. 0

d. +2

45. The oxidation number for carbon in CH₄ is

b. -2

c. 0

d. +2

e. +4

46. For the spontaneous process

MnO₄^- (aq) + 5 Fe²⁺ (aq) + 8 H⁺ (aq) ----------> Mn²⁺ (aq) + 5 Fe³⁺ (aq) + 4 H₂O (l)

The reducing agent is

47. For the spontaneous process

MnO₄^- (aq) + 5 Fe²⁺ (aq) + 8 H⁺ (aq) ----------> Mn²⁺ (aq) + 5 Fe³⁺ (aq) + 4 H₂O (l)

The stronger of the two potential reducing agents is

48. For the spontaneous process

MnO₄^- (aq) + 5 Fe²⁺ (aq) + 8 H⁺ (aq) ----------> Mn²⁺ (aq) + 5 Fe³⁺ (aq) + 4 H₂O (l)

E^o_cell must be

49. Table 18.1 tells us

Fe²⁺ (aq) ---------> Fe³⁺ (aq) + e^- E^o = -0.771 V

If the stoichiometric coefficients of the half reaction are all multiplied by 5 so that it can be combined with the half reaction MnO₄^- (aq) + 8 H⁺ (aq) + 5 e^- -----> Mn²⁺ (aq) + 4H₂O (l), the value of E^o used in the calculation of E_cell is

a. -0.386

c. -1.542 V

50. Exposure to small amounts of ionizing radiation is:

51. The process ₇¹⁴N + ₂⁴He -------> ₈¹⁷O + ₁¹H

52. Complete conversion of 1 g of matter to energy is equivalent to burning (in O_a.)

a. 2 kg C

b. 2000 kg C

d. 2 x 10⁹ kg C

17. A typical covalent bond energy is about

a. 20 kJ / mol bonds

c. 2000 kJ / mol bonds

18. In simple, small molecules, "hydrogen bonding" typically occurs

a. within one molecule

ANS. "Hydrogen bonding" is an intermolecular force.

19. The shape of the methane (CH₄) molecule is

a. flat, square planar

20. The shape of the ammonia (:NH₃) molecule is

a. flat

21. The shape of the formaldehyde (H₂C=O) molecule is

b. pyramidal

22. Vitamin A is predominantly

b. polar

23. Vitamin C is predominantly

a. nonpolar

24. Vitamin C is more soluble in

a. hexane

25. I₂ is

b. moderately polar

c. very polar

26. I₂ is

a. more soluble in water than in hexane.

c. equally soluble in water and in hexane.

d. insoluble in water and in hexane.

27. When liquid water boils at 100^o C, covalent bonds in the water molecules are broken.

a. true

28. Consider two systems at equilibrium: {CaCO₃ (s) <=====> Ca²⁺ (aq) + CO₃^2- (aq)}

Which statement is true?

a. [Ca²⁺] in the left system is less than [Ca²⁺] in the right system.

c. [Ca²⁺] in the left system is greater than [Ca²⁺] in the right system.

29. Northern pike (a fish) does not live in warm water because

a. it is a True Alaskan fish

c. many predators live in warm water

30. When a gas dissolves in a liquid, we can approximate DG = -TDS. Considering this, we would then predict that the solubility of a gas in a liquid

b. does not change with temperature

c. increases as the temperature increases

31. In a 0.010 M HNO₃ solution the [H₃O⁺] = 0.010 M. The [OH^-] is

32. A 0.001 M HBr solutions has a pH of about

The strong acid is completely dissociated. The hydronium ion concentration is 0.001 M.

33. A 0.001 M HOCl (hypochlorous acid) solutions has a pH of about

34. When NaHCO₃(s) is placed in water, you get mostly

35. A solutions with pH = 4.00 is more acidic than a solution with pH 6.0 by a factor of

36. What is the best "picture" of acetic acid (HAc) dissolved in water?

37. A solution of 0.026 M NH₃ is

38. A solution of 1.1 M HNO₂ is

39. When dissolved in water, which salt will produce a basic solution?

F^- (aq) + H₂O (l) < ===== > HF (aq) + OH^- (aq)

40. When 5 mmol of some strong acid, HX, is added to 4 mmol of some base, B, what happens?

a. It is not possible to say.

41. When 25 mL of 0.20 M NaOH and 40 mL of 0.10 M HCl mix and react

NaOH (aq) + HCl (aq) ------- > NaCl(aq) + H₂O (l)

The resulting solution is

42. When 25 mL 0.20 M NaCN and 40 mL 0.10 M HCl mix, the resulting solution contains as major protic (not NaCl) solutes

Note the similarities to the problem directly above.

NaCN (aq) + HCl (aq) ------- > NaCl(aq) + HCN (l)

43. Which solutes would give the best buffer at pH 10.6?

 1. Imagine mixing H₂(g) and I₂(g) so that [H₂]_i = 1.0 M, [I₂] _i = 2.0 M. Then cause them to react according to the rules of Chem 105.

H₂ (g) + I₂ (g) -----> 2 HI (g)

The concentration of HI when the reaction is done will be

2. The equilibrium constant expression, Kc, for

CaCO₃ (s) + 2H₂O+ ------ > Ca²⁺ (aq) + CO₂ (g) + 3 H₂O (l) is:

3. For COCl₂ (g) < ==== > CO (g) + Cl₂ (g) K₁ = 8 x 10^-4

If we turn the reaction around to CO (g) + Cl₂ (g) < ======= > COCl₂ (g), the value of K₂ will be

4. For the reaction

CO (g) + Cl₂ (g) < ======= > COCl₂ (g), K₂ = 1.2 x 10³.

If we multiply all of the stoichiometric coefficients by 2, we get

2 CO (g) + 2 Cl₂ (g) < ======= > 2 COCl₂ (g).

The values of K₃ for this new reaction is

 ANS: Since the new equilibrium constant expression ([COCl₂]² / [CO]²{Cl₂]²) is the square of the original ([COCl₂] / [CO] {Cl₂]), the numerical value is squared.

 5. Which picture best represents a solution of the strong acid, HCl?

6.

Assume you made an initial mixture of 0.01 M COCl₂ (g), 0.01 M CO (g), and 0.01 M Cl₂ (g). This is a nonequilibrium mixture. When the system reaches it equilibrium concentration, you should expect

 ANS: Since K is appreciably less than 1, this is a reactant favored process and we'd expect some COCl₂ (g) to be formed from CO (g) and Cl₂ (g). (The numerical result is 0.0163 M COCl₂, 0.0037 M CO, 0.0037 M Cl₂.

7. Consider the reaction:

A reaction mixture is examined and found to have this composition:

[H₂] = 0.050 M, [I₂] = 1.53 M, [HI] = 6.25 M.

 You can state

a. The system is at equilibrium. There will be no net change in concnetrations.

b. The system is still reacting. HI is being formed.

c. The system is still reacting. H₂ and I₂ are being formed.

 8. For the production of ammonia at 472 ^oC, Kc = 0.105.

N₂ (g ) + 3 H₂ (g) <=====> 2 NH₃ (g)

A particular closed system contains 0.1207 M H₂, 0.0402 M N₂, and 0.00272 M NH₃. This system is at equilibrium since

Qc = [NH₃]²_now/{[N₂] _now[NH₃] ³_now }= (0.00272)²/{(0.0402)(0.1207)³ }= 0.105

If some more H₂ is added to the system so that the concentration of H₂ has doubled to 0.2414 M, the system is still at equilibrium

Qc changes when more hydrogen is added:

9. Consider the following equilibrium process:

A 0.1 M cobalt solution, at equilibrium, is red. What is the effect of adding HCl to this solution.

a. No change. The solution remains red.

10. Aqueous CoCl₄^2-(aq) can be formed by mixing Co(H2O)₆²⁺(aq) with HCl(aq)

Assume you have made a solution containing approximately equal amounts of Co(H₂O)₆²⁺and CoCl₄^2- .

The addition of AgNO₃(aq) will

Addition of silver ions will consume chloride: Ag⁺ (aq) + Cl^- (aq) < ==== > AgCl (s). This causes Q to increase. The system responds by producing more chloride ion and the red Co(H₂O)₆²⁺(aq)

11. Aqueous CoCl₄^2-(aq) can be formed by mixing Co(H₂O)₆²⁺(aq) with HCl(aq)

Co(H₂O)₆²⁺(aq) + 4 Cl^-(aq) < ======= > CoCl₄^2-(aq) + 6 H₂O(l)

Delta H for the above reaction is >0.

Assume you have made a solution containing approximately equal amounts of Co(H₂O)₆²⁺and CoCl₄^2-and have a murky purple solution. To get a pure blue color you should

To get a blue solution, the reaction must respond to the temperature perturbation by producing more CoCl₄^2-(aq). When more CoCl₄^2-(aq) is produced, the system will cool because the reaction is endothermic. Thus, the perturbation should be to heat the solution to a higher temperature, so that the system will respond by cooling.

12. The gas pressure in a rigid container is 1.20 atm at room temperature (20^oC). When the temperature increases to 40^oC, the resulting gas pressure is

13. A balloon has a volume of 0.30 L at atmospheric pressure (760 torr). When it is placed in a vacuum chamber with pressure of 1/3 atm (253 torr), its volume will be

a. 0.10 L

b. 0.30 L

14. If the dotted curve in the plot below represents the velocity distribution of N₂ at 293K, the curve that represents the velocity distribution of N₂ at 393K is

a. A

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Created February 11, 2000

Updated April 20, 2000