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Chapter 2: The Mole

Balancing Chemical Equations

1. What will be the coefficient for HNO3 when the following equation is balanced?

Ba(OH)2(aq) + HNO3(aq) Ba(NO3)2(aq) + H2O(l)

(a) 1(b) 2(c) 3(d) 5(e) none of these

Answer: (b)

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2. What will be the coefficient for oxygen when the following equation is balanced?

C3H8(g) + O2 (g) CO2(g) + H2O(g)

(a) 1 (b) 2 (c) 3 (d) 5 (e) none of these

Answer: (d)

3. What will be the coefficient for NH3 when the following reaction is balanced?

NH3(g) + O2(g) N2(g) + H2O(l)

(a) 1(b) 3(c) 4(d) 5(e) none of these

Answer: (c)

4. Balance the following equations:

(I) Na2SO4(s) + C(s) Na2S(aq) + CO2(g)(II) Mg3N2(s) + H2O(l) Mg(OH)2(aq) + NH3(g)

Answer: (I) Na2SO4(s) + 2 C(s) Na2S(s) + 2 CO2(g)(II) Mg3N2(s) + 6 H2O(l) 3 Mg(OH)2(aq) + 2 NH3(g)

5. The balanced equation for the decomposition of ammonium dichromate has which of the following sets of coefficients?

A (NH4)2Cr2O7(s) B Cr2O3(s) + C N2(g) + D H2O(g)

(a) A = 2, B = 2, C = 2, D = 4 (b) A = 1, B = 1, C = 1, D = 4 (c) A = 1, B = 1, C = 1, D = 2 (d) A = 1, B = 1, C = 2, D = 2(e) A = B = C = D = 1

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Answer: (b)

6. Calculate the sum of the coefficients in the balanced chemical equation for the following reaction:

A H2S(g) + B O2(g) C SO2(g) + D H2O(g)(a) 6 (b) 8 (c) 9 (d) 11 (e) 17

Answer: (c)

7. What is the sum of the coefficients when the following chemical equation is balanced?

A Ca3(PO4)2(s) + B C(s) C Ca3P2(s) + D CO(g)(a) 6 (b) 12 (c) 18 (d) 20 (e) none of the above

Answer: (c)

8. Which illustration best represents the following equation?

2H2 + O2 2H2O

Answer: (c)

Mole Ratios and Chemical Equations

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9. If 0.50 moles of PbS are combined with 0.50 moles of O2, how many moles of PbO can be produced by the following reaction?

2 PbS(s) + 3 O2(g) 2 PbO(s) + 2 SO2(g)(a) 0.33(b) 0.50 (c) 0.75 (d) 2.0 (e) none of these

Answer: (a)

10. What would happen to the potential yield of sulfur dioxide in the previous question if the amount of oxygen was doubled?

(a) It would decrease by a factor of 2. (b) It would decrease by a factor of 1.5.

(c) It would remain constant. (d) It would increase by a factor of 1.5. (e) It would increase by a factor of 2.

Answer: (d)

11. Acetylene gas, C2H2, burns in the presence of oxygen by the following reaction:

2 C2H2(g) + 5 O2 (g) 2 H2O(l) + 4 CO2(g)

If 4.5 moles of acetylene gas are to be burned, how many moles of oxygen will be required for the complete reaction of the acetylene?

(a) 4.5 moles(b) 22.5 moles(c) 8.1 moles(d) 5.0 moles(e) none of these

Answer: (e)

12. For the reaction: 4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(l), how many moles of ammonia, NH3, are required to react completely with 0.250 moles of oxygen?

(a) 0.400(b) 0.500(c) 0.200

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(d) 0.313(e) 0.178

Answer: (c)

13. The molecular formula of iso-octane is C8H18. It burns in the presence of oxygen to form a mixture of CO2 and H2O. What is the ratio of moles of water to moles of carbon dioxide produced in this reaction?

(a) 1:1 (b) 2:1 (c) 9:4 (d) 9:8 (e) none of the above

Answer: (d)

14. A laboratory method for preparing oxygen (O2) involves the decomposition of KClO3.

KClO3(s) 2 KCI(s) + 3 O2(g)

How many moles of oxygen are produced when 0.135 moles of KCl are produced by this reaction?

(a) 0.135(b) 0.090(c) 0.203 (d) 0.405(e) none of these

Answer: (c)

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Stoichiometry

15. What mass of O2, in grams, is produced in the decomposition of 100 g of KClO3 by the following reaction?

2 KClO3(s) 2 KCl(s) + 3 O2(g)(a) 0.816 grams(b) 1.22 grams(c) 39.2 grams(d) 150 grams(e) 26.1 grams

Answer: (c)

16. Iron ore is impure Fe2O3. When Fe2O3 is heated with an excess of carbon (coke), iron metal is produced. How many moles of Fe can be produced from 250 g of Fe2O3 by the following reaction?

Fe2O3 (s) + 3 C(s) 2 Fe(l) + 3 CO(g)(a) 500(b) 125(c) 1.57(d) 3.13(e) 0.785

Answer: (d)

17. Calculate the number of moles of iron, Fe, produced when 0.500 moles of carbon monoxide, CO, react with an excess of iron oxide.

Fe2O3(s) + 3 CO(g) 2 Fe(s) + 3 CO2(g)

(a) 2.00 moles (b) 1.00 moles (c) 0.750 moles (d) 0.166 moles(e) none of these

Answer: (e)

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18. Hydrogen chloride, HCI, can be made by the reaction of phosphorus trichloride, PCl3, with water and then boiling the HCI gas out of the solution. Calculate the mass of HCI gas that can be prepared from 15.0 g of PCl3 and an excess of water.

PCl3(g) + 3 H2O(l) 3 HCI(aq) + H3PO3(aq)(a) 0.328 g (b) 3.97 g (c) 11.9 g(d) 35.7 g(e) 3.00 g

Answer: (c)

19. Ethyl alcohol, C2H5OH, is also known as drinking alcohol. It can be produced by the fermentation of glucose by the following reaction.

C6H12O6(aq) 2 C2H5OH(aq) + 2 CO2(g)

How many moles of ethanol can be produced from 100 g of glucose?

(a) 100 moles(b) 200 moles(c) 0.556 moles(d) 1.11 moles(e) none of these

Answer: (d)

20. Nitrogen reacts with red-hot magnesium to form magnesium nitride,

3 Mg(s) + N2(g) Mg3N2(s)

which reacts with water to form magnesium hydroxide and ammonia,

Mg3N2(s) + 6 H2O(l) 3 Mg(OH)2(aq) + 2 NH3(aq)

How many grams of magnesium would you have to start with to prepare 15.0 grams of ammonia?

(a) 13.3 g (b) 15.0 g (c) 20.0 g (d) 32.2 g

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(e) none of the above

Answer: (d)

21. The chemical formula of ethanol is C2H6O. It burns in the presence of excess oxygen to form CO2 and H2O. How many grams of H2O are produced from the combustion of 25.0 g of ethanol?

(a) 9.78 g (b) 18.0 g (c) 25.0 g (d) 29.3 g (e) 54.1 g

Answer: (d)

22. Sucrose, or “cane sugar,” has the formula C12H22O11. What weight of carbon dioxide can be produced from 10.0 grams of sucrose and 10.0 grams of oxygen?

C12H22O11(s) + 12 O2(g) 12 CO2(g) + 11 H2O(g)

(a) less than 5 grams (b) between 5 and 10 grams (c) between 10 and 15 grams(d) between 15 and 20 grams (e) more than 20 grams

Answer: (d)

23. PF3 reacts with XeF4 to give PF5. In theory, how many moles of PF5 can be produced from 100.0 g of PF3 and 50.0 g of XeF4?

2 PF3(g) + XeF4(s) 2 PF5(g) + Xe(g)(a) 0.121 mol (b) 0.241 mol (c) 0.482 mol (d) 1.14 mol (e) 2.28 mol

Answer: (c)

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24. The portable stoves campers use for cooking burn propane, C3H8.

A C3H8(g) + B O2(g) C CO2(g) + D H2O(g)

What weight of propane would have to be burned to form 7.26 g of CO2?

(a) 2.42 g (b) 4.84 g (c) 7.26 g (d) 21.8 g (e) none of the above

Answer: (a)

25. Calculate the weight of O2 needed to burn 10.0 grams of hydrogen sulfide, H2S.

A H2S + B O2 C SO2 + D H2O(a) 4.70 g (b) 6.26 g (c) 7.04 g (d) 9.39 g (e) 14.1 g

Answer: (e)

26. How many grams of CO2 gas are produced from the combustion of 10.0 grams of iso-octane?

2 C8H18 + 25 O2 16 CO2 + 18 H2O

(a) 1.58 g (b) 3.85 g (c) 14.19 g (d) 30.82 g (e) 35.02 g

Answer: (d)

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27. A crucible and sample of CaCO3, weighing 42.670 g, was heated until red hot in order to decompose the sample.

CaCO3(s) CaO(s) + CO2(g)

The crucible weighed 35.351 g. What is the theoretical weight of the crucible and residue after the decomposition is complete?

(a) 3.219 g (b) 4.100 g (c) 38.570 g (d) 39.451 g (e) 49.989 g

Answer: (d)

28. Nitrogen reacts with hydrogen to form ammonia

N2(g) + 3 H2(g) 2 NH3(g)

which burns in the presence of oxygen to form nitrogen oxide,

4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g)

which reacts with excess oxygen to form nitrogen dioxide.

2 NO(g) + O2(g) 2 NO2(g)

How much nitrogen would we have to start with to make 10 moles of nitrogen dioxide?

(a) 2.5 mol (b) 5 mol (c) 10 mol (d) 15 mol (e) 20 mol

Answer: (b)

29. How many grams of hydrogen peroxide, H2O2, must decompose by the following reaction to produce 0.400 moles of O2?

2 H2O2(aq) 2 H2O(l) + O2(g)

(a) less than 25 grams (b) between 25 and 40 grams (c) between 40 and 60 grams (d) between 60 and 80 grams

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(e) more than 80 grams

Answer: (b)Limiting Reagents

30. In the following reaction 10.0 grams of lead sulfide, PbS are allowed to react with 5.00 grams of oxygen, O2. Determine the limiting reagent, the number of grams of PbO that can be produced and the number of moles of reactant that remains unreacted.

2 PbS(s) + 3 O2(g) 2 PbO(s) + 2 SO2(g)

Answer: PbS, 9.33 g PbO, 0.93 moles O2 remaining

31. Iron metal reacts with chlorine gas by the following reaction.

2 Fe(s) + 3 Cl2 2 FeCl3

(I) Predict the moles of product formed if 31.67 grams of Fe reacts with an excess of chlorine gas, Cl2.

(II) Predict the moles of product formed if 0.567 moles of Fe reacts with 0.718 moles of chlorine gas, Cl2.

(III) What is fundamentally different about how the above two problems must be solved?

Answer: (I) 0.567 moles(II) 0.479 moles(III) In part (b) you must find the limiting reagent.

32. How many grams of HCl are produced when 10.0 g of Cl2 and 1.00 g of H2 react?

H2(g) + Cl2(g) 2 HCl(g)(a) 5.14 g (b) 9.04 g (c) 10.3 g (d) 11.0 g (e) 18.1 g

Answer: (c)

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33. What would happen to the amount of HCl produced in the previous question if the amount of H2 is doubled?

(a) It would decrease by more than a factor of two. (b) It would decrease by a factor of two. (c) It would remain the same. (d) It would increase by a factor of two. (e) It would increase by more than a factor of two.

Answer: (c)

Questions 34-35 refer to the following reaction:

2 NO(g) + O2(g) 2 NO2(g)

34. What is the limiting reagent when 10.0 g of NO react with 10.0 g of O2 to form NO2?

(a) NO (b) O2 (c) NO2 (d) none of these (e) There aren't enough data to answer the question.

Answer: (a)

35. How many moles of the limiting reagent are present in the previous problem?

(a) 0.313 (b) 0.333 (c) 0.435 (d) 0.625 (e) none of these

Answer: (b)

36. How many grams of MgO can be produced by burning 10.0 grams of Mg in the presence of 10.0 grams of O2?

(a) 10.0 g (b) 12.6 g (c) 16.6 g

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(d) 20.0 g (e) 25.2 g

Answer: (c)37. When glucose reacts with oxygen in living systems, carbon dioxide and

water are produced, and a great deal of energy is liberated.

C6H12O6(s) + 6 O2(g) 6 CO2(g) + 6 H2O(g)

What weight of carbon dioxide can be produced from the reaction of 10.0 grams of glucose with 10.0 grams of oxygen?

(a) 2.29 g (b) 2.44 g (c) 13.8 g (d) 14.7 g (e) none of these

Answer: (d)

Density

38. The density of sugar is 1.59 g/mL. Calculate the volume of a teaspoon of sugar if this quantity of sugar weighs 4.50 grams.

(a) 0.140 mL (b) 0.353 mL (c) 2.83 mL (d) 6.09 mL (e) 7.16 mL

Answer: (c)

39. Iron has a density of 7.86 g/cm3. When iron rusts, it forms hydrated Fe2O3 that has a density of 5.12 g/cm3. What happens to the material as iron rusts?

(a) It expands. (b) It contracts. (c) The volume must remain the same. (d) The iron evaporates.(e) The water evaporates.

Answer: (a)

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40. The first silver dollar minted in the Americas was 3.95 cm in diameter and contained 27.07 grams of silver. If the density of silver is 10.5 g/cm3, what was the height of each coin?

(a) 0.00791 cm (b) 0.0316 cm (c) 0.0526 cm (d) 0.210 cm (e) none of these

Answer: (d)

41. The density of water in pounds per cubic foot is 62.4 lb/ft3. If a 2 ft3 bag of mulch sold at the local lawn care center weighs 30 lbs, which of the following correctly describes what happens when this mulch is poured on water?

(a) The mulch will sink because it is less dense than water. (b) The mulch will sink because it is more dense than water. (c) The mulch will float because it is less dense than water. (d) The mulch will float because it is more dense than water. (e) There is no way of predicting what will happen.

Answer: (c)

42. A sample of sucrose (C12H22O11) that weighs 9.35 g is placed in a 15.00 mL flask. The remaining volume of the flask is filled with benzene — a liquid in which sucrose does not dissolve. The density of benzene is 0.879 g/cm3. The sucrose and benzene together weigh 17.33 g. What is the density of sucrose?

(a) 0.532 g/cm3 (b) 0.623 g/cm3 (c) 1.03 g/cm3 (d) 1.16 g/cm3 (e) 1.58 g/cm3

Answer: (e)

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43. The following liquids don’t mix with water. Which of these liquids would float on top of water?

(I) benzene, C6H6, d = 0.877 g/cm3 (II) carbon disulfide, CS2, d = 1.263 g/cm3 (III) chloroform, CHCl3, d = 1.483 g/cm3

(IV) ether, (C2H5)2O, d = 0.714 g/cm3 (V) gasoline, d = 0.675 g/cm3

(a) I, II and III (b) II and III (c) I, IV and V(d) None of these liquids would float on top of water.(e) All of these liquids would float on top of water.

Answer: (c)

44. If a beaker that contains 250 mL of chloroform (CHCl3) weighs 524 grams, what is the weight of the beaker? (CHCl3: d = 1.483 g/cm3)

(a) about 50 g (b) about 100 g (c) about 150 g (d) about 250 g (e) about 500 g

Answer: (c)

45. A student was given three pieces of metal that looked like brass. Sample I had a volume of 17.3 mL and weighed 154.3 g, sample II had a volume of 28.4 mL and weighed 547.2 g, and sample III had a volume of 22.2 mL and weighed 186.1 g. Which sample(s) was (were) brass? (Brass: d 8 g/cm3)

(a) only I (b) I and II (c) I and III (d) II and III (e) All of these samples were brass.

Answer: (c)

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46. Retailers purchase gasoline by weight so they get a constant amount of gasoline per dollar (as long as the price is constant). We buy gasoline by volume. 1.000 kg of gasoline occupies a volume of 1.356 L at 15.6oC. What volume of gasoline would you have to purchase to get the same weight at 32.2oC when gasoline has a density of 0.72210 g/mL?

(a) 0.9792 L(b) 0.7221 L(c) 1.848 L(d) 1.385 L(e) 1.215 L

Answer: (d)

Concentration & Molarity

47. The amount of solute in each of the beakers shown below is represented by the number of black dots. The volume is shown on the side. In which beaker does the solute have the highest concentration?

(a) Beaker A(b) Beaker B(c) Beaker C(d) Beaker D(e) The solute concentration is the same in each beaker.

Answer: (d)

48. What is the molarity of 0.0250 liters of a solution containing 7.50 grams of a compound whose molar mass is 152.8 g/mole?

(a) 0.125 M(b) 0.509 M(c) 0.491 M

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(d) 1.96 M(e) 3.92 M

Answer: (d)

49. What weight of HNO3 is present in 13.0 mL of 0.0872 M HNO3?

(a) 0.0714 g(b) 0.422 g(c) 0.0180 g(d) 9.39 g(e) 0.181 g

Answer: (a)

50. How many moles of Na2SO4 are in 250 mL of a 0.150 M Na2SO4 solution?

(a) 0.0375(b) 0.600(c) 1.67(d) 6.00 x 10–4

(e) none of these

Answer: (a)

51. How many grams of NaNO3 are required to prepare 2.00 L of a 0.250 M NaNO3 solution?

(a) 0.500 g(b) 84.9 g(d) 170 g(d) 42.5 g(e) 680 g

Answer: (d)

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52. Calculate the molarity of a solution prepared by dissolving 10.0 grams of NaOH and then diluting the solution to 500 mL.

(a) 0.251 M(b) 0.501 M(c) 1.99 M(d) 3.99 M(e) 7.98 M

Answer: (b)

53. Calculate the molarity of a 20.0% by weight solution of CuCl2 in water if the density of this solution is 1.205 g/cm3.

Answer: 1.79 M

54. What volume of a solution of sulfuric acid that is 60.0% by weight H2SO4 (MW = 98 g/mol, d = 1.50 g/cm3) would be required to prepare 500.0 mL of a 1.50 M solution?

Answer: 81.7 mL

55. Calculate the concentration of a solution prepared by dissolving 10.0 grams of NaNO3 in enough water to give 250.0 mL of solution.

(a) 0.0294 M (b) 0.118 M (c) 0.471 M (d) 2.13 M (e) 8.50 M

Answer: (c)

56. What is the molarity of concentrated phosphoric acid if this solution is 85.5% H3PO4 by weight and it has a density of 1.70 g/mL?

(a) less than 5 M (b) 14.8 M (c) 17.3 M (d) 20.3 M (e) none of the above

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Answer: (b)

57. How many mL of 15 M NH3 would you need to make 15.0 mL of a 3.6 M NH3 solution?

(a) 0.036 mL (b) 0.63 mL (c) 3.6 mL (d) 8.1 mL (e) 360 mL

Answer: (c)

The following four questions (58-61) are based on the diagram above which describes the following lab procedure. Ten mL of an initial solution is pipetted into

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a volumetric flask. The 10.00 mL of initial solution is diluted to 100.0 mL with solvent to form the stock solution. Twenty five mL of the stock solution is then pipetted into another 100.0 mL volumetric flask and diluted to the 100.0 mL mark to form the final solution. The glassware in the diagram has been labeled with letters.

58. Which of the following statements correctly describes the relationship between moles of solute in the labeled containers?

(a) B > A(b) D > E(c) C = D(d) B = C (e) A = C

Answer: (d)

59. Which of the following statements correctly describes the relationship between the concentrations of solute in the labeled containers?

(a) B > A(b) D > E(c) C < D(d) B = C (e) A < C

Answer: (b)

60. Which of the following statements correctly describes the relationship between moles of solute in the labeled containers?

(a) A = C(b) A = B(c) D > C(d) D > E (e) C > E

Answer: (e)

61. Which of the following statements correctly describes the relationship between the concentrations of solute in the labeled containers?

(a) D = E

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(b) C = D(c) A > B(d) C > B (e) E > C

Answer: (b)

62. Calculate the concentration of a solution prepared by diluting 10.00 mL of a 0.15 M solution of KCl to 250 mL.

(a) 8.05 x 10–5 M(b) 5.36 x 10–4M(c) 6.00 x 10–3M(d) 0.0805 M(e) 3.75 M

Answer: (c)

63. How many mL of a 0.250 M K2SO4 solution is required to prepare 500 mL of a 0.080 M K2SO4 solution?

(a) 125 mL(b) 160 mL (c) 174 mL(d) 220 mL(e) 1.56 x 103 mL

Answer: (b)

Solution Stoichiometry

64. How much HgS forms when 113 mL of a 0.75 M CaS solution is mixed with 52 mL of a 1.21 M Hg(NO3)2 solution?

(a) 6.30 g (b) 8.48 g (c) 14.6 g (d) 19.7 g (e) none of the above

Answer: (c)

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65. If adding 22.7 mL of 0.6 M HCl to 1.00 L of a solution of AgNO3 precipitated 1.95 g of AgCl, what was the concentration of the original AgNO3 solution?

AgNO3(aq) + HCl(aq) AgCl(s) + HNO3(aq)

(a) 1.36 x 10–5 M (b) 1.36 x 10–2 M (c) 0.027 M (d) 0.68 M (e) 13.6 M

Answer: (b)

66. A 2.50 g sample of a bronze gong was cut out and dissolved in sulfuric acid. The copper sulfate produced was mixed with KI to form CuI and the triiodide ion, I3

–. The I3– ion was then titrated with thiosulfate, S2O3

2–.

Cu(s) + 2 H2SO4(aq) CuSO4(aq) + SO2(g)+ 2 H2O(l)

2 CuSO4(aq) + 5 I–(aq) 2 CuI(s) + I3–(aq) + 2 SO4

2–(aq)

I3–(aq) + 2 S2O3

2–(aq) 3 I–(aq) + S4O62–(aq)

If it took 31.5 mL of 1.00 M thiosulfate for this titration, how many moles of copper were present in the original 2.50 g sample?

(a) 0.0105 (b) 0.0158 (c) 0.0315 (d) 0.0630 (e) 0.0945

Answer: (c)

67. On April 19, 1995 a bomb exploded, killing 168 people, wounding hundreds of others and destroying the Alfred P. Murrah Federal Building in Oklahoma City. The explosive mixture used in this incident contained ammonium nitrate, NH4NO3, which is commonly used as a fertilizer. What is the molarity of concentrated nitric acid, HNO3(aq), if it takes 5.63 mL of the acid to consume 15.00 mL of 6.00 M NH3(aq)?

NH3(aq) + HNO3(aq) NH4NO3(aq)

(a) less than 1 M

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(b) between 1 and 5 M (c) between 5 and 10 M(d) between 10 and 15 M (e) more than 15 M

Answer: (e)

68. One way of determining blood alcohol levels is by titrating a sample of blood according to the following net ionic equation.

C2H5OH(aq) + 2 Cr2O72–(aq) + 16 H+(aq) 2 CO2(g) + 4 Cr3+(aq) + 11 H2O(l)

If 8.76 mL of 0.04988 M Cr2O72– is required for the titration of a 10.00 mL

sample of blood, what was the molarity of the alcohol present in the blood sample?

(a) less than 0.01 M (b) between 0.01 and 0.03 M (c) between 0.03 and 0.06 M (d) between 0.06 and 0.09 M (e) more than 0.1 M

Answer: (b)

69. The reaction between fructose and the periodate ion is described by the following equation.

C6H12O6(aq) + 5 IO4–(aq) 5 IO3

–(aq) + 5 HCO2H(aq) + H2CO(aq)

Calculate the molarity of a fructose solution if 22.35 mL of 1.050 M IO4– is

required to consume 12.56 mL of this solution.

(a) less than 0.25 M (b) between 0.25 M and 0.5 M (c) between 0.5 M and 1.5 M(d) between 1.5 M and 2 M (e) more than 2 M

Answer: (b)

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