Answers and Explanations

1. (A) The volume of a gas increases as temperature increases provided that pressure remains constant. This is a direct proportion. Heating a balloon is a good example.

2. (C) The volume of a gas decreases as the pressure is increased provided that the temperature is held constant. This is shown by the inversely proportional curve in (C). The pressure increasing on a closed cylinder is a good example.

3. (E) The graph shows that there is a starting quantity in solution, and a slight positive slope to the right indicates a directly proportional change in the solubility as temperature rises.

4. (A) This is the definition of any molecule.

5. (B) A commercial cake mix is a mixture of ingredients, which are themselves compounds.

6. (C) This is the definition of an isotope.

7. (E) An acid salt contains one or more H atoms in the salt formula separating a positive ion and the hydrogen-bearing negative ion. For example, Na₂SO₄ is a normal salt and NaHSO₄ is an acid salt because of the presence of H in the hydrogen sulfate ion. In Ca(HCO₃)₂, the same is true. This is classified as an acid salt.

8. (C) An atom with atomic number 9 would have a 2,7 electron configuration, which matches the outer energy level of iodine.

9. (B) There are 2 Na, 1 C, and 3 O, which add to 6 atoms.

10. (A) pH from 0 to 6 is acid, 7 is neutral, and 8 to 14 is basic. The most acidic value listed is 1.

11. (E) Molarity is defined as moles of solute/liter of solution.

12. (A) Gas densities can be expressed in grams/liter.

13. (C) Molar mass is not affected by pressure and temperature.

14. (A) If the density of a gas is known, the mass of 1 L can be multiplied by 22.4 to find the molecular mass because 1 mole occupies 22.4 L at STP.

15. (A) Buffers resist changes in pH.

16. (B) Color change is the function of indicators.

17. (C) On the pH scale, from 0 to 6 is acid and 7 is neutral.

18. (D) On the pH scale, from 8 to 14 is basic.

19. (E) The ozone (O₃) in the stratosphere absorbs ultraviolet rays from the sun.

20. (C) When hydrocarbons containing C and H do not have enough oxygen to combust with O₂(g) completely, the product will be CO, carbon monoxide.

21. (A) 2KClO₃ → 2KCl + 3O₂(g) is the reaction that occurs.

22. (D) CO₂ is slightly soluble in water, forming carbonic acid, H₂CO₃, which is a weak acid.

23. (B) SO₂ has the highest molar mass. Graham's Law describes the rate of effusion of a gas as inversely related (by the square root) to the molar mass of the gas.

101. (T, F) The assertion is true, but the degree of motion of gas molecules is directly related to the temperature.

102. (T, F) An electron does have a dual nature. It can behave as a particle or a wave. As a wave, it has a wavelength and a frequency. As a particle, it has mass.

103. (F, T) Alkanes are simple hydrocarbons that have all single bonds. In ethane, C₂H₆, all the bonds are single covalent. In ethene, C₂H₄, there is a double bond between the two carbon atoms. Ethene is an alkene.

104. (T, F) When metal atoms ionize, they lose electrons and become smaller because the outermost electrons now exist at a lower energy level. The lower energy level is closer to the nucleus. The assertion is true, but the reason is false.

105. (T, T, CE) A negative heat of formation indicates that the reaction is exothermic and that the enthalpy change is negative.

106. (T, T, CE) Water is a polar molecule because there is unequal sharing of bonding electrons that are not symmetrically arranged in the molecule.

107. (T, T, CE) This is a function of a catalyst—to speed up a reaction without permanently changing itself. The assertion and reason are both true.

108. (F, T) The Cu is losing electrons and thus being oxidized; the assertion is false. It is furnishing electrons and thus is a reducing agent; the reason is true.

109. (F, T) H₂ = 2, He = 4 (molar mass); inversely is the rate of diffusion of hydrogen to helium. When simplified, that's a ratio of 1.4 to 1. Hence the assertion is false, but the reason is true.

110. (T, T, CE) Since the gas is being heated at constant pressure, it expands. The temperatures are converted to kelvins (K) by adding 273° to the Celsius readings. The fraction must be ,                                     and this will increase the volume.

111. (F, T) Gibbs free energy is useful in indicating the conditions under which a chemical reaction will occur. Therefore, the equation can be used to predict the spontaneity of a reaction. Change in enthalpy and change in entropy are both part of the Gibbs free-energy equation: ΔG = ΔH − TΔS.

112. (F, F) Water is hydrogen and oxygen by weight. Both the assertion and the reason are false.

113. (T, T, CE) The specific heat of water is 1 cal/g°C. Therefore, 80.0 calories will raise 4.00 grams of water by 20.0°C.

114. (F, T) The balanced reaction is 2H₂ + O₂ → 2H₂O. The coefficients of this gaseous reaction show that 2 liters of hydrogen react with 1 liter of oxygen. This would leave 1 liter of unreacted oxygen. The limiting factor is the hydrogen.

115. (T, F) The reason why water is a good solvent is false. The reason why water generally dissolves ionic or other polar molecular substances is that “like dissolves like.”

24. (C) The energy necessary to get the reaction started, which is the activation energy, is shown at C.

25. (E) 2KClO₃ → 2KCl + 3O₂(g) shows that 2.00 moles of KClO₃ yield 3 moles of O₂:

    

26. (B) A catalyst can speed up a reaction by lowering the activation energy needed to start the reaction and then keep it going.

27. (E) The atomic number gives the number of protons in the nucleus and the total number of electrons. The mass number indicates the total number of protons and neutrons in the nucleus—for Na, 23 (11 protons + 12 neutrons).

28. (B) For gases, this is expressed as grams per liter. Since 1 molar mass of a gas occupies 22.4 L, 17 g/22.4 L = 0.76 g/L.

29. (B) Choice III is made up of elements from extreme sides of the Periodic Table and that therefore form ionic bonds.

30. (B) Only III is a ring hydrocarbon of the aromatic series.

31. (C) Since Li is higher in Group 1 than Na and since K is higher than Cs, Li and K have smaller radii and hence higher ionization energies than Na and Cs, respectively. Al is to the right of Na, and therefore Al has a higher ionization energy.

32. (D) Only II and III are redox reactions. The first reaction is a precipitation reaction. PbS is the precipitate, and the oxidation states of the substances in the reaction are not changing. The second equation is a combustion reaction. The oxidation states of carbon and oxygen change from −4 to +4 and 0 to −2, respectively. The third reaction is a synthesis reaction. The oxidation states of hydrogen and oxygen change from 0 to +1 and 0 to −2, respectively.

33. (A) These answers are based on the fact that the total of the assigned oxidation numbers times their occurrence for all the atoms in a compound is zero.

34. (D) These answers are based on the fact that the total of the assigned oxidation numbers times their occurrence for all the atoms in a compound is zero.

35. (D) These answers are based on the fact that the total of the assigned oxidation numbers times their occurrence for all the atoms in a compound is zero.

36. (B) This orbital configuration shows 6 electrons in the third energy level. The atom would like to gain 2e⁻ to fill the 3p orbital and thereby gain a −2 oxidation number.

37. (D) With this structure, the atom will tend to lose these electrons and get a +2 charge.

38. (E) A pipette is used to transfer an exact volume of liquid from one container to another.

39. (C) A condenser tube is used in distillation.

40. (D) A funnel is used to hold the filter paper.

41. (E) The pressure in the bottle would be less than atmospheric pressure by the Hg equivalent height of the 30 mm of water above the level in the collecting pan. This is calculated as 40.8 mm water/(13.6 mm water/1 mm Hg) and must be subtracted from atmospheric pressure. The other adjustment is to subtract the vapor pressure of water that is in the hydrogen gas since it was collected over water. This pressure is given as 30.0 mm Hg. Subtracting each of these from 730.mm Hg, the given atmospheric pressure, results in 730. mm − 40.8 mm/13.6 − 30.0 mm.

42. (B) The equilibrium shifts in the direction that tends to relieve the stress and thus regain equilibrium.

43. (C) The thermal reaction shows 2 moles of hydrogen reacting, or 4 g. Therefore, 8 g would release twice the amount of energy:

    

44. (B) The reaction would not be spontaneous because gold is less active than zinc. This could be determined by looking at the activity series for metals. Gold is the least active of all the metals and will not replace another metal in a compound spontaneously.

45. (D) Since Ag⁺ + 1e⁻ → Ag⁰, 1 mole of electrons yields 1 mole of silver  atoms. Therefore, 4 moles of electrons yields 4 moles of silver atoms.

46. (E) and since HCl ionizes completely, there would be 5.0 moles of H⁺ ions and 5.0 moles of Cl⁻ ions.

47. (D) K_sp = [Ag⁺][C₂H₃O₂⁻] = [2 × 10⁻³][2 × 10⁻³]

    (Since

    

    the silver ion and acetate ion concentrations are equal.)

    

48. (B) The great deal of hydrogen bonding between H₂O molecules explains the observed high boiling point and high freezing point of water compared with hydrogen sulfide.

49. (E)

    

    Since pH + pOH = 14, pOH = 14 − 5 = 9.

50. (B) 1 mole of H₂SO₄ contains 1 molar mass of sulfur, that is, 32 g of sulfur.

51. (B) N₂O = 44 g/mol

    (2 × 14) + 16 = 44

    1 mole of a gas occupies 22.4 L, so 44 g/22.4 L = 1.99 g/L.

52. (D) CH₂ = 14

    12 + 2 = 14 molecular mass

    56 ÷ 14 = 4

    Then 4 × CH₂ = C₄H₈.

53. (C) Only insoluble gases can be collected in this way.

54. (C) HCl is very soluble in water and denser than air, so it is suited to being collected by Method 2.

55. (D)

    

56. (D) The gram-molecular mass of H₂ is 2 grams. Since 4 grams is 2 moles and each mole occupies 22.4 liters,  2 × 22.4 = 44.8 L.

57. (D)

    

    

    Then x = 4.0 mol.

58. (C)

    

    

    Then x = 44.8 L.

59. (C)

    

    

    or

    

    Then x = 44.8 L.

60. (A) The energy required to melt ice at 0°C is called the heat of fusion of ice; 7.00 g of ice to water = 7.00 g × (80 cal/g) = 560 cal. The energy required to boil water at 100°C is called the heat of vaporization of water. The value is given as 540 cal/g. Therefore, 560 cal would boil about 1 gram of water.

61. (A) In the combustion reaction between methane and oxygen, carbon dioxide and water are produced. The oxidation state of carbon increases from −4 to +4 and the oxidation state of oxygen decreases from 0 to −2. Combustion reactions are also redox reactions.

62. (E) CO₂ is a reactant in photosynthesis, not a product. The reaction is

    

    or

63. (D)

    Let x = moles of H₂ and also of I₂ that combine to form HI.

    At equilibrium, [H₂] = 3 − x, [I₂] = 3 − x, and [HI] = 2x.

    

64. (D) In a closed system, decreasing the size of the container will cause the pressure to increase. When pressure is applied to an equilibrium involving gases, the reaction that lowers the pressure by decreasing the number of molecules will increase in rate. In this reaction, the rate of the reverse reaction, in which 2 molecules are decreased to 1, increases, thus reducing pressure while also producing more N₂O₄. The equilibrium constant is changed only by a change in temperature. Thus, II and III are true.

65. (A) This is Rutherford’s famous artificial transmutation experiment, done in 1919. The missing particle is an atom of oxygen-17 because mass number and atomic number must be conserved on each side of the equation.

66. (B)

    

    

67. (E) Percent is by mass, so 10.% is 0.10 × 1,000. g or 100. g.

68. (D) Since colligative properties, like freezing point, are related to the concentration of the solute particles, you would need only  of the number of moles of aluminum chloride compared to ethanol because AlCl₃ dissociates into four times as many particles upon dissolving than ethanol (a nonelectrolyte).

69. (C) The nuclear reactions shown release: (A) a neutron, (B) an alpha particle, (C) a beta particle, (D) no particles, and (E) a positron. The spontaneous emission of electrons from the nucleus of an atom is called beta radiation.

70. (D) The density of a gas at STP can be determined by dividing the molar mass of the gas by 22.4 L (the molar volume of a gas at STP). The molar mass of ammonia is 17.0 grams per mole. Divide 17.0 g per mol by 22.4 L per mole to calculate the density of approximately 1 g/L.