# Chapter 5, Calculations and the Chemical Equation

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1 1. How many iron atoms are present in one mole of iron? Ans atoms 2. How many grams of sulfur are found in mol of sulfur? [Use atomic weight: S, amu] Ans g 3. How many moles of sulfur are found in atoms of sulfur? [Use atomic weight: S, amu] Ans mol 4. How many atoms are present in a 7.31 g sample of copper? [Use atomic weight: Cu, amu] Ans atoms 5. What is the mass, in grams, of 1.79 mol of helium, the gas commonly used to fill party balloons and lighter-than-air ships? [Use atomic weight: He, 4.00 amu] Ans g 6. An iodine sample contains atoms of iodine. What is its mass in grams? [Use atomic weight: I, amu] Ans g 7. Give the symbol(s) needed to show the smallest unit of nitrogen as it is normally found in nature. Ans. N 2 8. When a solid compound is described as a "hydrate", what does this mean? he compound contains water molecules in its structure. 9. What is the difference in meaning between "2O" and "O 2 " when they occur in chemical equations? Ans. 2O means 2 separate atoms of oxygen, not combined in the form of a molecule. O 2 means a molecule of oxygen, i.e. two atoms bonded to each other molecules of a covalent compound is equal to how many moles of that compound? Ans. 1 mol 11. What is the mass, in grams, of one mole of diatomic hydrogen? [Use molar mass: H, 1.0 g/mol] Ans. 2.0 g 12. How many molecules of water are there in 5.00 mol of water? Ans molecules 13. If one atom of oxygen weighs amu, what will one mole of oxygen (O 2 ) weigh? Ans g General, Organic, and Biochemistry, 3/e Page 29

2 14. Dinitrogen monoxide or laughing gas (N 2 O) is used as a dental anesthetic and as an aerosol propellant. How many moles of N 2 O are present in 12.6 g of the compound? [Use atomic weights: N, amu, O, amu] Ans mol 15. Dinitrogen monoxide or laughing gas (N 2 O) is used as a dental anesthetic and as an aerosol propellant. How many molecules of N 2 O are present in 12.6 g of the compound? [Use atomic weights: N, amu, O, amu] Ans molecules 16. What law states that matter cannot be gained or lost during a chemical reaction? Ans. law of conservation of mass 17. What does the symbol "(aq)", often found in chemical equations, mean? he reactant or product to which this applies is aqueous, i.e. dissolved in water. 18. In chemical equations, what are the meanings of the symbols s, l and g, used in parentheses? Ans. s = solid; l = liquid; g = gas 19. Balance the following equation: Ca(s) + HCl(g) CaCl 2 (s) + H 2 (g) Ans. Ca(s) + 2HCl(g) CaCl 2 (s) + H 2 (g) 20. Balance the following equation: Mg(OH) 2 (s) + HCl(g) MgCl 2 (s) + H 2 O(l) Ans. Mg(OH) 2 (s) + 2HCl(g) MgCl 2 (s) + 2H 2 O(l) 21. Balance the following equation: Na(s) + Cl 2 (g) NaCl(s) Ans. 2Na(s) + Cl 2 (g) 2NaCl(s) 22. Balance the equation for the combustion of octane, a component of gasoline, using smallest whole number coefficients: C 8 H 18 (l) + O 2 (g) CO 2 (g) + H 2 O(l) Ans. 2C 8 H 18 (l) + 25O 2 (g) 16CO 2 (g) + 18H 2 O(l) 23. Balance the equation for the complete oxidation of glucose (C 6 H 12 O 6 ), an important metabolic process: C 6 H 12 O 6 (l) + O 2 (g) CO 2 (g) + H 2 O(l) Ans. C 6 H 12 O 6 (l) + 6O 2 (g) 6CO 2 (g) + 6H 2 O(l) 24. How many moles of hydrogen gas are needed to react with oxygen to form two moles of water? 2H 2 (g) + O 2 (g) 2H 2 O(l) Ans. 2 mol 25. How many moles of oxygen gas are needed to react with hydrogen to form one mole of water? 2H 2 (g) + O 2 (g) 2H 2 O(l) Ans. 0.5 mol General, Organic, and Biochemistry, 3/e Page 30

3 26. How many grams of sodium hydroxide will react with g of aqueous HCl? [Use formula weights: NaOH, amu; HCl, amu] NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l) Ans g 27. Calculate the number of grams of oxygen that must react with g of C 3 H 8 to produce only carbon dioxide and water. [Use atomic weights: C, amu; H, 1.01 amu; O, amu] Ans g 28. Iron reacts with oxygen to form iron(iii) oxide (Fe 2 O 3 ). How many grams of product will be formed from 5.00 grams of Fe? [Use atomic weights: Fe, amu; O, amu] Ans g 29. Glucose (C 6 H 12 O 6 ) is an important energy-rich compound, produced by photosynthesis: 6CO 2 (g) + 6H 2 O(l) C 6 H 12 O 6 (l) + 6O 2 (g) What mass of glucose, in grams, can be produced from 2.61 mol of CO 2 and the necessary water? [Use atomic weights: H, 1.01 amu; C, 12.01; 0, 16.00] Ans g 30. Explain what is meant by the term "limiting reactant" in a chemical reaction. Ans. If the amount of one reactant at the start of reaction is less than that required to react completely with the other reactants, according to the balanced equation, it is the limiting reactant. 31. Magnesium hydroxide (Mg(OH) 2 ), as "Milk of Magnesia" can be used to neutralize excess stomach acid, represented by HCl(aq): Mg(OH) 2 (s) + 2HCl(aq) MgCl 2 (aq) + 2H 2 O(l) When 5.00 g each of Mg(OH) 2 and HCl are combined, which is the limiting reactant, and what mass of MgCl 2 can be produced? [Use atomic weights: H, 1.01 amu; O, amu; Mg, amu; Cl, amu] Ans. HCl is limiting reactant; 6.53 g of MgCl 2 can be produced. 32. To convert a given number of moles into the number of atoms, you would multiply by which of the following factors? Ans. A A atoms/1 mol B. 1 mol/ atoms C atoms/1 mol D. 1 mol/ atoms E. molar mass General, Organic, and Biochemistry, 3/e Page 31

4 33. To convert from a given mass in grams to the number of moles, you would multiply by which of the following factors? A. 1/Avogadro's number B. Avogadro's number/1 C. molar mass/l D. 1/molar mass E. Avogadro's number/molar mass 34. To convert from a given number of atoms to the number of moles, you would multiply by which of the following factors? A. Avogadro's number/1 B. 1/Avogadro's number C. 1/molar mass D. molar mass/1 E. Avogadro's number/molar mass 35. To convert from a given number of grams to the number of atoms, you would multiply by which of the following factors? A. Avogadro's number/1 B. 1/Avogadro's number C. 1/molar mass D. molar mass/1 E. Avogadro's number/molar mass Ans. E 36. The average mass of one atom of iron is amu. What is the mass of Avogadro's number of atoms? A centigrams B g C kg D atoms E formula units 37. What is the weight, in grams, of one mole of hydrogen atoms? [Use atomic weight: H, 1.01 amu] Ans. A A g B g C g D g E g General, Organic, and Biochemistry, 3/e Page 32

5 38. How many grams of sulfur make up 3.01 mol of sulfur? [Use atomic weight: S, amu] A g B g C g D g E g Ans. E 39. How many moles are there in one ounce (28.4 g) of pure gold? [Use atomic weight: Au, amu] A mol B mol C mol D mol E mol Ans. C 40. How many atoms of sulfur are present in 155 g of sulfur? [Use atomic weight: S, amu] A atoms B atoms C atoms D atoms E atoms Ans. A 41. How many iron atoms are present in 3.01 mol of iron? A B C D E What is the formula weight of carbon dioxide? [Use atomic weights: C, amu; O, amu] Ans. C A amu B g C amu D g E mol General, Organic, and Biochemistry, 3/e Page 33

6 43. Aspirin is the common name for acetyl salicylic acid, C 9 H 8 O 4. A tablet has g of aspirin. How many moles is this? [Use formula weight: aspirin, amu] A mol B mol C mol D. 554 mol E mol 44. How many grams are there in mol of nicotine, a yellow liquid? [Use formula weight: nicotine, amu] A g B g C g D g E g Ans. C 45. How many molecules are there in mol of nicotine, a yellow liquid? A molecules B molecules C molecules D molecules E molecules 46. How many molecules are their in g of aspirin? [Use formula weight: aspirin, amu] A molecules B molecules C molecules D molecules E molecules Ans. A 47. What number will be found in front of "Al" when the following equation is balanced with smallest whole number coefficients? Al(s) + O 2 (g) Al 2 O 3 (s) A. 1 B. 2 C. 3 D. 4 E. 8 General, Organic, and Biochemistry, 3/e Page 34

7 48. How many moles of HCl can be formed when 2 mol of hydrogen gas react with chlorine? H 2 (g) + Cl 2 (g) HCl(g) (unbalanced) A. 0.5 mol B. 1 mol C. 2 mol D. 4 mol E. 8 mol 49. Which of the choices is the correctly balanced form of the following equation? C 6 H 14 (l) + O 2 (g) CO 2 (g) + H 2 O(l) A. C 6 H 14 (l) + 13O 2 (g) 6CO 2 (g) + 7H 2 O(l) B. C 6 H 14 (l) + 19O(g) 6CO 2 (g) + 7H 2 O(l) C. C 6 H 14 (l) + 19O 2 (g) 6CO 2 (g) + 7H 2 O(l) D. 2C 6 H 14 (l) + 19O 2 (g) 12CO 2 (g) + 14H 2 O(l) E. C 12 H 28 (l) + 38O(g) 12CO 2 (g) + 14H 2 O(l) 50. How many moles of hydrogen gas are needed to react with oxygen to form one mole of water? 2H 2 (g) + O 2 (g) 2H 2 O(l) A. 0.5 mol B. 1 mol C. 2 mol D. 4 mol E. 6 mol 51. Calculate the mass in grams of oxygen needed to react with mol of C 3 H 8 to form carbon dioxide and water. [Use atomic weight: O, amu] C 3 H 8 (g) + O 2 (g) CO 2 (g) + H 2 O(l) (unbalanced) A g B g C g D g E g Ans. E 52. Iron reacts with oxygen to form iron(iii) oxide (Fe 2 O 3 ). How many grams of product will be formed from g of Fe? [Use atomic weights: Fe, amu; O, amu] A g B g C g D g E g 53. Consider the hypothetical reaction: 3A 2 + 2B C + 2D How many moles of D can be formed from 5.0 mol of A 2 and excess B? A. 1.7 mol B. 3.3 mol C. 6.7 mol D. 7.5 mol E. 10. mol 54. T F One atomic mass unit is the same as one gram. 55. T F The smallest complete unit of iron is an atom of iron. General, Organic, and Biochemistry, 3/e Page 35

8 56. T F One mole of iron atoms contains molecules. 57. T F The formula weight of a compound is calculated by adding together the number of atoms that make it up. 58. T F Strictly speaking, it is incorrect to use the term "molecular weight" in referring to ionic compounds. 59. T F One mole of Ca 3 (PO 4 ) 2 contains atoms of calcium. 60. T F One mole of oxygen gas contains molecules. 61. T F The formula weight of water is equal to g. 62. T F If the atomic weight of hydrogen is 1.01 amu, a mole of H 2 will weigh 1.01 g. 63. T F One gram of gold (atomic weight 197 amu) contains more atoms than one gram of copper (atomic weight amu). 64. T F One mole of H 2 O contains a total of atoms. 65. T F The law of conservation of mass states that matter cannot be gained or lost during a chemical reaction. 66. T F The symbol, above or below the reaction arrow in an equation, indicates that heating is needed for the reaction to take place. 67. T F Counting the number of moles on both the reactant and product sides of an equation is the first step in balancing the equation. 68. T F In a correctly balanced equation, the number of moles of reactants and the number of moles of products may differ. 69. T F The term "dynamic equilibrium" is used to describe the condition of a reaction when one of the reactants has been completely used up. General, Organic, and Biochemistry, 3/e Page 36

9 70. T F 0.5 mol of oxygen gas can react with hydrogen gas to form 1.0 mol of water. General, Organic, and Biochemistry, 3/e Page 37

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