TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY

Transcription

1 CHAPTER FOUR TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY Questions 9. "Slightly soluble" refers to substances that dissolve only to a small extent. A slightly soluble salt may still dissociate completely to ions and, hence, be a strong electrolyte. An example of such a substance is Mg(OH) 2. It is a strong electrolyte, but not very soluble. A weak electrolyte is a substance that doesn't dissociate completely to produce ions. A weak electrolyte may be very soluble in water, or it may not be very soluble. Acetic acid is an example of a weak electrolyte that is very soluble in water. 10. Measure the electrical conductivity of a solution and compare it to the conductivity of a solution of equal concentration of a strong electrolyte. Exercises Aqueous Solutions: Strong and Weak Electrolytes a. NaBr(s) Na (aq) + Br (aq) b. MgCl 2(s) Mg (aq) + 2 Cl (aq) Your drawing should show equal numbers of Na and Br ions. 2+ Your drawing should show twice the number of Cl ions as Mg ions. 61

2 62 CHAPTER 4 SOLUTION STOICHIOMETRY c. Al(NO 3) 3(s) Al (aq) + 3 NO 3(aq) d. (NH 4) 2SO 4(s) 2 NH 4(aq) + SO 4 (aq) For ei, your drawings should show equal numbers of the cations and anions present as each salt is a 1:1 salt. The ions present are listed in the following dissolution reactions e. NaOH(s) Na (aq) + OH (aq) f. FeSO 4(s) Fe (aq) + SO 4 (aq) g. KMnO 4(s) K (aq) + MnO 4(aq) h. HClO 4(aq) H (aq) + ClO 4(aq) i. NH4C2H3O 2(s) NH 4 (aq) + C2H3O 2(aq) a. Ba(NO 3) 2(aq) Ba (aq) + 2 NO 3(aq); Picture iv represents the Ba and NO3 ions present in Ba(NO ) (aq). 3 2 b. NaCl(aq) Na (aq) + Cl (aq); Picture ii represents NaCl(aq). + 2 c. K2CO 3(aq) 2 K (aq) + CO 3 (aq); Picture iii represents K2CO 3(aq) d. MgSO 4(aq) Mg (aq) + SO 4 (aq); Picture i represents MgSO 4(aq) CaCl 2(s) Ca (aq) + 2 Cl (aq) MgSO 4(s) Mg (aq) + SO 4 (aq); NH4NO 3(s) NH 4 (aq) + NO 3(aq) Solution Concentration: Molarity a g NaHCO 3 = mol NaHCO3 M = = M NaHCO 3 4 b g K2Cr2O 7 = mol K2Cr2O7 M = 3 = M KCrO 2 2 7

3 CHAPTER 4 SOLUTION STOICHIOMETRY c g Cu = mol Cu = mol Cu M = 3 2+ = M Cu ml = 1.3 mol C2H5OH; Molarity = = 5.2 M CHOH a. CaCl 2(s) Ca (aq) + 2 Cl (aq); = 0.15 M; = 2(0.15) = 0.30 M 3 b. Al(NO 3) 3(s) Al (aq) + 3 NO 3(aq); = 0.26 M; = 3(0.26) = 0.78 M + 2 c. K2Cr2O 7(s) 2 K (aq) + Cr2O 7 (aq); = 2(0.25) = 0.50 M; = 0.25 M 3+ 2 d. Al 2(SO 4) 3(s) 2 Al (aq) + 3 SO 4 (aq) = M = M 18. a. = = 1.00 M 2 Ca(NO 3) 2(s) Ca (aq) + 2 NO 3(aq); = 1.00 M; = 2(1.00) = 2.00 M b. = = 2.0 M + 2 Na2SO 4(s) 2 Na (aq) + SO 4 (aq); = 2(2.0) = 4.0 M; = 2.0 M c g NH4Cl = mol NH4Cl = M NH4Cl(s) NH 4 (aq) + Cl (aq); = = M 3 d g K3PO 4 = mol K3PO4

4 64 CHAPTER 4 SOLUTION STOICHIOMETRY = = M + 3 K3PO 4(s) 3 K (aq) + PO 4 (aq); = 3(0.0188) = M; = M mol solute = volume (L) molarity ; AlCl 3(s) Al (aq) + 3 Cl (aq) mol Cl = L = mol Cl 2 2 MgCl 2(s) Mg (aq) + 2 Cl (aq) mol Cl = L = mol Cl 2 NaCl(s) Na (aq) + Cl (aq) mol Cl = L = mol Cl ml of 0.30 M AlCl 3 contains the most moles of Cl ions. 20. NaOH(s) Na (aq) + OH (aq), 2 total mol of ions (1 mol Na and 1 mol Cl ) per mol NaOH L = mol ions 2 BaCl 2(s) Ba (aq) + 2 Cl (aq), 3 total mol of ions per mol BaCl L = mol ions + 3 Na3PO 4(s) 3 Na (aq) + PO 4 (aq), 4 total mol of ions per mol Na3PO L = mol ions 75.0 ml of M Na3PO 4 contains the largest number of ions. 21. Molar mass of NaHCO 3 = (16.00) = g/mol

5 CHAPTER 4 SOLUTION STOICHIOMETRY 65 Volume = g NaHCO 3 = L = 41.7 ml 41.7 ml of M NaHCO 3 contains g NaHCO Molar mass of NaOH = = g/mol Mass NaOH = L = 4.00 g NaOH 23. a L = 20.0 g NaOH Place 20.0 g NaOH in a 2 L volumetric flask; add water to dissolve the NaOH, and fill to the mark with water, mixing several times along the way. b L = L Add 500. ml of 1.00 M NaOH stock solution to a 2 L volumetric flask; fill to the mark with water, mixing several times along the way. c L = 38.8 g K2CrO4 Similar to the solution made in part a, instead using 38.8 g K2CrO 4. d L = L Similar to the solution made in part b, instead using 114 ml of the 1.75 M K2CrO 4 stock solution. 24. a L solution = 0.50 mol H2SO mol H2SO 4 = L conc. H2SO 4 or 28 ml Dilute 28 ml of concentrated H2SO 4 to a total volume of 1.00 L with water. b. We will need 0.50 mol HCl mol HCl = L = 42 ml Dilute 42 ml of concentrated HCl to a final volume of 1.00 L. c. We need 0.50 mol NiCl 2.

6 66 CHAPTER 4 SOLUTION STOICHIOMETRY 0.50 mol NiCl 2 = g NiCl2 6H2O 120 g Dissolve 120 g NiCl2 6H2O in water, and add water until the total volume of the solution is 1.00 L. d L = 0.50 mol HNO mol HNO 3 = L = 31 ml Dissolve 31 ml of concentrated reagent in water. Dilute to a total volume of 1.00 L. e. We need 0.50 mol Na2CO mol Na2CO 3 = 53 g Na2CO3 Dissolve 53 g Na2CO 3 in water, dilute to 1.00 L g (NH 4) 2SO 4 = mol (NH 4) 2SO4 Molarity = = M (NH ) SO Moles of (NH 4) 2SO 4in final solution L = mol Molarity of final solution = = M (NH ) SO (NH 4) 2SO 4(s) 2 NH 4(aq) + SO 4 (aq); = 2(0.136) = M; = M 26. mol Na2CO 3 = L = 0.21 mol Na2CO3 Na CO (s) 2 Na (aq) + CO (aq); mol Na = 2(0.21) = 0.42 mol mol NaHCO 3 = L = mol NaHCO3 + NaHCO 3(s) Na (aq) + HCO 3(aq); mol Na = mol = = = 4.5 M Na Stock solution =

7 CHAPTER 4 SOLUTION STOICHIOMETRY L stock = g steroid This is diluted to a final volume of ml. 8 = M steroid 28. Stock solution: g Mn = mol Mn ; = M Solution A contains: ml = mol Mn Molarity = = M Solution B contains: ml = mol Mn Molarity = = M Solution C contains: L = mol Mn Molarity = = M Precipitation Reactions 29. In these reactions, soluble ionic compounds are mixed together. To predict the precipitate, switch the anions and cations in the two reactant compounds to predict possible products; then use the solubility rules in Table 4.1 to predict if any of these possible products are insoluble (are the precipitate). a. Possible products = BaSO 4 and NaCl; precipitate = BaSO 4(s) b. Possible products = PbCl 2 and KNO 3; precipitate = PbCl 2(s) c. Possible products = Ag3PO 4 and NaNO 3; precipitate = Ag3PO 4(s) d. Possible products = NaNO 3 and Fe(OH) 3; precipitate = Fe(OH) 3(s) 30. a. Possible products = FeCl 2 and K2SO 4; Both salts are soluble so no precipitate forms. b. Possible products = Al(OH) 3 and Ba(NO 3) 2; precipitate = Al(OH) 3(s) c. Possible products = CaSO 4 and NaCl; precipitate =CaSO 4(s) d. Possible products = KNO and NiS; precipitate = NiS(s) 3

8 68 CHAPTER 4 SOLUTION STOICHIOMETRY 31. For the following answers, the balanced molecular equation is first, followed by the complete ionic equation, then the net ionic equation. a. BaCl 2(aq) + Na2SO 4(aq) BaSO 4(s) + 2 NaCl(aq) Ba (aq) + 2 Cl (aq) + 2 Na (aq) + SO (aq) BaSO (s) + 2 Na (aq) + 2 Cl (aq) Ba (aq) + SO (aq) BaSO (s) b. Pb(NO 3) 2(aq) + 2 KCl(aq) PbCl 2(s) + 2 KNO 3(aq) 2 Pb (aq) + 2 NO 3(aq) + 2 K (aq) + 2 Cl (aq) PbCl 2(s) + 2 K (aq) + 2 NO 3(aq) 2 Pb (aq) + 2 Cl (aq) PbCl 2(s) c. 3 AgNO 3(aq) + Na3PO 4(aq) Ag3PO 4(s) + 3 NaNO 3(aq) Ag (aq) + 3 NO 3(aq) + 3 Na (aq) + PO 4 (aq) Ag3PO 4(s) + 3 Na (aq) + 3 NO 3(aq) Ag (aq) + PO 4 (aq) Ag3PO 4(s) d. 3 NaOH(aq) + Fe(NO 3) 3(aq) Fe(OH) 3(s) + 3 NaNO 3(aq) 3 3 Na (aq) + 3 OH (aq) + Fe (aq) + 3 NO 3(aq) Fe(OH) 3(s) + 3 Na (aq) + 3 NO 3(aq) 3 Fe (aq) + 3 OH (aq) Fe(OH) 3(s) 32. a. No reaction occurs since all possible products are soluble salts. b. 2 Al(NO 3) 3(aq) + 3 Ba(OH) 2(aq) 2 Al(OH) 3(s) + 3 Ba(NO 3) 2(aq) Al (aq) + 6 NO 3(aq) + 3 Ba (aq) + 6 OH (aq) 2 Al(OH) 3(s) + 3 Ba (aq) + 6 NO 3(aq) 3 Al (aq) + 3 OH (aq) Al(OH) 3(s) c. CaCl 2(aq) + Na2SO 4(aq) CaSO 4(s) + 2 NaCl(aq) Ca (aq) + 2 Cl (aq) + 2 Na (aq) + SO (aq) CaSO (s) + 2 Na (aq) + 2 Cl (aq) Ca (aq) + SO (aq) CaSO (s) d. K2S(aq) + Ni(NO 3) 2(aq) 2 KNO 3(aq) + NiS(s) K (aq) + S (aq) + Ni (aq) + 2 NO 3 (aq) 2 K (aq) + 2 NO 3(aq) + NiS(s) 2+ 2 Ni (aq) + S (aq) NiS(s)

9 CHAPTER 4 SOLUTION STOICHIOMETRY a. When CuSO (aq) is added to Na S(aq), the precipitate that forms is CuS(s). Therefore, Na (the grey spheres) and SO (the blueishgreen spheres) are the spectator ions CuSO 4(aq) + Na2S(aq) CuS(s) + Na2SO 4(aq); Cu (aq) + S (aq) CuS(s) b. When CoCl 2(aq) is added to NaOH(aq), the precipitate that forms is Co(OH) 2(s). Therefore, Na + (the grey spheres) and Cl (the green spheres) are the spectator ions. 2 CoCl 2(aq) + 2 NaOH(aq) Co(OH) 2(s) + 2 NaCl(aq); Co (aq) + 2 OH (aq) Co(OH) 2(s) + c. When AgNO 3(aq) is added to KI(aq), the precipitate that forms is AgI(s). Therefore, K (the red spheres) and NO (the blue spheres) are the spectator ions. 3 AgNO 3(aq) + KI(aq) AgI(s) + KNO 3(aq); Ag (aq) + I (aq) AgI(s) 34. There are many acceptable choices for spectator ions. We will generally choose Na and NO 3 as the spectator ions because sodium salts and nitrate salts are usually soluble in water. a. Fe(NO 3) 3(aq) + 3 NaOH(aq) Fe(OH) 3(s) + 3 NaNO 3(aq) b. Hg 2(NO 3) 2(aq) + 2 NaCl(aq) Hg2Cl 2(s) + 2 NaNO 3(aq) c. Pb(NO 3) 2(aq) + Na2SO 4(aq) PbSO 4(s) + 2 NaNO 3(aq) d. BaCl 2(aq) + Na2CrO 4(aq) BaCrO 4(s) + 2 NaCl(aq) 35. a. (NH 4) 2SO 4(aq) + Ba(NO 3) 2(aq) 2 NH4NO 3(aq) + BaSO 4(s) Ba (aq) + SO (aq) BaSO (s) b. Pb(NO 3) 2(aq) + 2 NaCl(aq) PbCl 2(s) + 2 NaNO 3(aq) 2 Pb (aq) + 2 Cl (aq) PbCl 2(s) c. Potassium phosphate and sodium nitrate are both soluble in water. No reaction occurs. d. No reaction occurs since all possible products are soluble. e. CuCl 2(aq) + 2 NaOH(aq) Cu(OH) 2(s) + 2 NaCl(aq) 2 Cu (aq) + 2 OH (aq) Cu(OH) 2(s) 36. a. CrCl (aq) + 3 NaOH(aq) Cr(OH) (s) + 3 NaCl(aq) Cr (aq) + 3 OH (aq) Cr(OH) 3(s) b. 2 AgNO 3(aq) + (NH 4) 2CO 3(aq) Ag2CO 3(s) + 2 NH4NO 3(aq) Ag (aq) + CO 3 (aq) Ag2CO 3(s)

10 70 CHAPTER 4 SOLUTION STOICHIOMETRY c. CuSO 4(aq) + Hg 2(NO 3) 2(aq) Cu(NO 3) 2(aq) + Hg2SO 4(s) 2+ 2 Hg 2 (aq) + SO 4 (aq) Hg2SO 4(s) d. No reaction occurs since all possible products (SrI 2 and KNO 3) are soluble. 37. Three possibilities are: Addition of K2SO 4 solution to give a white ppt. of PbSO 4. Addition of NaCl solution to give a white ppt. of PbCl. Addition of K CrO solution to give a bright yellow ppt. of PbCrO Since no precipitates formed upon addition of NaCl or Na2SO 4, we can conclude that Hg 2 and Ba 2+ are not present in the sample since Hg2Cl 2 and BaSO 4 are insoluble salts. However, Mn may be 2+ present since Mn does not form a precipitate with either NaCl or Na2SO 4. Since a precipitate formed 2 with NaOH, the solution must contain Mn because it forms a precipitate with OH [Mn(OH) (s)] AgNO 3(aq) + Na2CrO 4(aq) Ag2CrO 4(s) + 2 NaNO 3(aq) L = g Na2CrO Na3PO 4(aq) + 3 Pb(NO 3) 2(aq) Pb 3(PO 4) 2(s) + 6 NaNO 3(aq) L = L 41. A1(NO 3) 3(aq) + 3 KOH(aq) Al(OH) 3(s) + 3 KNO 3(aq) = 250. ml Na3PO L = mol Al(NO 3) L = mol KOH From the balanced equation, 3 mol of KOH are required to react with 1 mol of Al(NO 3) 3 (3:1 mol ratio). The actual KOH to Al(NO 3) 3mol ratio present is / = 2 (2:1). Since the actual mol ratio present is less than the required mol ratio, KOH is the limiting reagent mol KOH = g Al(OH) The balanced equation is: 3 BaCl 2(aq) + Fe 2(SO 4) 3(aq) 3 BaSO 4(s) + 2 FeCl 3(aq) ml BaCl 2 = mol BaCl2

11 CHAPTER 4 SOLUTION STOICHIOMETRY ml Fe 2(SO 4) 3 = mol Fe 2(SO 4) 3 The required mol BaCl 2 to mol Fe 2(SO 4) 3ratio from the balanced reaction is 3:1. The actual mol ratio is / = 1 (1:1). This is well below the required mol ratio, so BaCl is the limiting reagent mol BaCl 2 = 2.33 g BaSO AgNO 3(aq) + CaCl 2(aq) 2 AgCl(s) + Ca(NO 3) 2(aq) mol AgNO 3 = L = mol AgNO3 mol CaCl 2 = L = mol CaCl2 The required mol AgNO 3to mol CaCl 2ratio is 2:1 (from the balanced equation). The actual mol ratio present is 0.020/0.015 = 1.3 (1.3:1). Therefore, AgNO is the limiting reagent. 3 mass AgCl = mol AgNO 3 = 2.9 g AgCl The net ionic equation is: Ag (aq) + Cl (aq) AgCl(s). The ions remaining in solution are the 2+ + unreacted Cl ions and the spectator ions, NO 3 and Ca (all Ag is used up in forming AgCl). The mol of each ion present initially (before reaction) can be easily determined from the mol of each reactant mol AgNO 3 dissolves to form mol Ag and mol NO mol CaCl2 2 dissolves to form mol Ca and 2(0.015) = mol Cl. mol unreacted Cl = mol Cl initially mol Cl reacted = mol Cl unreacted = M Cl The molarity of the spectator ions are: 2+ = 0.10 M NO 3 ; = M Ca 44. a. Cu(NO 3) 2(aq) + 2 KOH(aq) Cu(OH) 2(s) + 2 KNO 3(aq) Solution A contains 2.00 L 2.00 mol/l = 4.00 mol Cu(NO 3) 2and solution B contains 2.00 L 3.00 mol/l = 6.00 mol KOH. Lets assume in our picture that we have 4 formula units 2 of Cu(NO 3) 2(4 Cu ions and 8 NO 3 ions) and 6 formula units of KOH (6 K ions and 6 OH 2 2+ ions). With 4 Cu ions and 6 OH ions present, then OH is limiting. One Cu ion remains as 3

12 72 CHAPTER 4 SOLUTION STOICHIOMETRY Cu(OH) 2(s) formula units form as precipitate. The following drawing summarizes the ions that remain in solution and the relative amount of precipitate that forms. Note that K and NO3 ions are spectator ions. In the drawing, V 1 is the volume of solution A or B and V 2 is the volume of the combined solutions with V 2 = 2 V 1. The drawing exaggerates the amount of precipitate that would actually form. b. The spectator ion concentrations will be onehalf of the original spectator ion concentrations in the individual beakers because the volume was doubled. Or using moles, = = 1.50 M and = 2.00 M. The concentration of OH ions will be zero 2+ since OH is the limiting reagent. From the drawing, the number of Cu ions will decrease by a factor of four as the precipitate forms. Since the volume of solution doubled, the concentration 2+ of Cu ions will decrease by a factor of eight after the two beakers are mixed: = M Alternately, one could certainly use moles to solve for : mol Cu reacted = 2.00 L = 3.00 mol Cu reacted mol Cu present initially = 2.00 L = 4.00 mol Cu present initially excess Cu present after reaction = 4.00 mol 3.00 mol = 1.00 mol Cu excess = M AcidBase Reactions mass of precipitate = 6.00 mol KOH = 293 g Cu(OH) All the bases in this problem are ionic compounds containing OH. The acids are either strong or weak electrolytes. The best way to determine if an acid is a strong or weak electrolyte is to memorize all the strong electrolytes (strong acids). Any other acid you encounter that is not a strong acid will be a weak

13 CHAPTER 4 SOLUTION STOICHIOMETRY 73 electrolyte (a weak acid) and the formula should be left unaltered in the complete ionic and net ionic equations. The strong acids to recognize are HCl, HBr, HI, HNO 3, HClO 4 and H2SO 4. For the answers below, the order of the equations are molecular, complete ionic and net ionic. a. 2 HClO 4(aq) + Mg(OH 2)(s) 2 H2O(l) + Mg(ClO 4) 2(aq) 2 2 H (aq) + 2 ClO 4(aq) + Mg(OH) 2(s) 2 H2O(l) + Mg (aq) + 2 ClO 4(aq) H (aq) + Mg(OH) 2(s) 2 H2O(l) + Mg (aq) b. HCN(aq) + NaOH(aq) H2O(l) + NaCN(aq) HCN(aq) + Na (aq) + OH (aq) H2O(l) + Na (aq) + CN (aq) HCN(aq) + OH (aq) H2O(l) + CN (aq) c. HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) H (aq) + Cl (aq) + Na (aq) + OH (aq) H2O(l) + Na (aq) + Cl (aq) H (aq) + OH (aq) H2O(l) 46. a. 3 HNO 3(aq) + Al(OH) 3(s) 3 H2O(l) + Al(NO 3) 3(aq) 3 3 H (aq) + 3 NO 3(aq) + Al(OH) 3(s) 3 H2O(l) + Al (aq) + 3 NO 3(aq) H (aq) + Al(OH) 3(s) 3 H2O(l) + Al (aq) b. HC2H3O 2(aq) + KOH(aq) H2O(l) + KC2H3O 2(aq) HC2H3O 2(aq) + K (aq) + OH (aq) H2O(l) + K (aq) + C2H3O 2(aq) HC2H3O 2(aq) + OH (aq) H2O(l) + C2H3O 2(aq) c. Ca(OH) 2(aq) + 2 HCl(aq) 2 H2O(l) + CaCl 2(aq) 2 2 Ca (aq) + 2 OH (aq) + 2 H (aq) + 2 Cl (aq) 2 H2O(l) + Ca (aq) + 2 Cl (aq) 2 H (aq) + 2 OH (aq) 2 H2O(l) or H (aq) + OH (aq) H2O(l) 47. All the acids in this problem are strong electrolytes. The acids to recognize as strong electrolytes are HCl, HBr, HI, HNO, HClO and H SO a. KOH(aq) + HNO 3(aq) H2O(l) + KNO 3(aq) K (aq) + OH (aq) + H (aq) + NO 3(aq) H2O(l) + K (aq) + NO 3(aq) + OH (aq) + H (aq) H2O(l)

14 74 CHAPTER 4 SOLUTION STOICHIOMETRY b. Ba(OH) 2(aq) + 2 HCl(aq) 2 H2O(l) + BaCl 2(aq) 2 2 Ba (aq) + 2 OH (aq) + 2 H (aq) + 2 Cl (aq) 2 H2O(l) + Ba (aq) + 2 Cl (aq) + 2 OH (aq) + 2 H (aq) 2 H2O(l) or OH (aq) + H (aq) H2O(l) c. 3 HClO 4(aq) + Fe(OH) 3(s) 3 H2O(l) + Fe(ClO 4) 3(aq) 3 3 H (aq) + 3 ClO 4(aq) + Fe(OH) 3(s) 3 H2O(l) + Fe (aq) + 3 ClO 4(aq) H (aq) + Fe(OH) 3(s) 3 H2O(l) + Fe (aq) 48. a. AgOH(s) + HBr(aq) AgBr(s) + H2O(l) AgOH(s) + H (aq) + Br (aq) AgBr(s) + H2O(l) AgOH(s) + H (aq) + Br (aq) AgBr(s) + H2O(l) b. Sr(OH) 2(aq) + 2 HI(aq) 2 H2O(l) + SrI 2(aq) 2 2 Sr (aq) + 2 OH (aq) + 2 H (aq) + 2 I (aq) 2 H2O(l) + Sr (aq) + 2 I (aq) + 2 OH (aq) + 2 H (aq) 2 H2O(l) or OH (aq) + H (aq) H2O(l) c. Cr(OH) 3(s) + 3 HNO 3(aq) 3 H2O(l) + Cr(NO 3) 3(aq) 3 Cr(OH) 3(s) + 3 H (aq) + 3 NO 3(aq) 3 H2O(l) + Cr (aq) + 3 NO 3(aq) + 3+ Cr(OH) 3(s) + 3 H (aq) 3 H2O(l) + Cr (aq) 49. If we begin with ml of M NaOH, then: L = mol NaOH is to be neutralized. a. NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) mol NaOH = L or 100. ml b. HNO 3(aq) + NaOH(aq) H2O(l) + NaNO 3(aq) mol NaOH = L or 66.7 ml c. HC2H3O 2(aq) + NaOH(aq) H2O(l) + NaC2H3O 2(aq)

15 CHAPTER 4 SOLUTION STOICHIOMETRY mol NaOH = L or 50.0 ml We begin with ml of M HCl or L mol/l = mol HCl. a. HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) mol HCl = L or 50.0 ml b. 2 HCl(aq) + Ba(OH) 2(aq) 2 H2O(l) + BaCl 2(aq) mol HCl = L = 50.0 ml c. HCl(aq) + KOH(aq) H2O(l) + KCl(aq) mol HCl = L or 20.0 ml 51. HNO 3(aq) + NaOH(aq) NaNO 3(aq) + H2O(l) 15.0 g NaOH = mol NaOH L = mol HNO 3 We have added more moles of NaOH than mol of HNO 3 present. Since NaOH and HNO 3 react in a 1:1 mol ratio, NaOH is in excess and the solution will be basic. The ions present after reaction will be the excess OH ions and the spectator ions, Na and NO. The moles of ions present initially are: mol NaOH = mol Na = mol OH = mol mol HNO 3 = mol H = mol NO 3 = mol The net ionic reaction occurring is: H (aq) + OH (aq) H2O(l) The mol of excess OH remaining after reaction will be the initial mol of OH minus the amount of OH + neutralized by reaction with H : mol excess OH = mol mol = mol OH excess The concentration of ions present is: 3 = 2.25 M OH

16 76 CHAPTER 4 SOLUTION STOICHIOMETRY + = M NO 3 ; = 2.50 M Na 52. Ba(OH) 2(aq) + 2 HCl(aq) BaCl 2(aq) + 2 H2O(l); H (aq) + OH (aq) H2O(l) L = mol HCl = mol H mol Cl L = mol Ba(OH) 2 = mol Ba mol OH + The net ionic equation requires a 1:1 mol ratio between OH and H. The actual mol OH to mol H ratio is greater than 1:1 so OH is in excess. 2 2 Since mol OH will be neutralized by the H, we have ( ) 10 = mol OH remaining in excess. 2 = M OH 53. HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) L NaOH = mol HCl Molarity of HCl = = M HCl HNO 3(aq) + Ca(OH) 2(aq) 2 H2O(l) + Ca(NO 3) 2(aq) L HNO 3 = L = 43.8 ml Ca(OH) Since KHP is a monoprotic acid, the reaction is: NaOH(aq) + KHP(aq) H2O(l) + NaKP(aq) Mass KHP = L NaOH = g KHP 56. NaOH(aq) + KHP(aq) NaKP(aq) + H2O(l) g KHP = mol NaOH

17 CHAPTER 4 SOLUTION STOICHIOMETRY 77 4 There are mol of sodium hydroxide in ml of solution. Therefore, the concentration of sodium hydroxide is: 2 = M NaOH OxidationReduction Reactions 57. Apply rules in Table 4.2. a. KMnO 4is composed of K and MnO 4 ions. Assign oxygen a value of 2, which gives manganese a +7 oxidation state since the sum of oxidation states for all atoms in MnO 4 must equal the 1 charge on MnO. K, +1; O, 2; Mn, b. Assign O a 2 oxidation state, which gives nickel a +4 oxidation state. Ni, +4; O, c. K4Fe(CN) 6 is composed of K cations and Fe(CN) 6 anions. Fe(CN) 6 is composed of iron and CN anions. For an overall anion charge of 4, iron must have a +2 oxidation state. d. (NH ) HPO is made of NH cations and HPO anions. Assign +1 as the oxidation state of H and 2 as the oxidation state of O. In NH, x + 4(+1) = +1, x = 3 = oxidation state of N. In HPO, +1 + y + 4(2) = 2, y = +5 = oxidation state of P e. O, 2; P, +3 f. O, 2; Fe, + 8/3 g. O, 2; F, 1; Xe, +6 h. F, 1; S, +4 i. O, 2; C, +2 j. Na, +1; O, 2; C, a. UO 2 : O, 2; For U, x + 2(2) = +2, x = +6 b. As2O 3: O, 2; For As, 2(x) + 3(2) = 0, x = +3 c. NaBiO 3: Na, +1; O, 2; For Bi, +1 + x + 3(2) = 0, x = +5 d. As 4: As, 0 e. HAsO 2: assign H = +1 and O = 2; For As, +1 + x + 2(2) = 0; x = f. Mg2P2O 7: Composed of Mg ions and P2O 7 ions. Oxidation states are: Mg, +2; O, 2; P, g. Na2S2O 3: Composed of Na ions and S2O 3 ions. Na, +1; O, 2; S, +2 h. Hg2Cl 2: Hg, +1; Cl, 1 2 i. Ca(NO 3) 2: Composed of Ca ions and NO 3 ions. Ca, +2; O, 2; N, +5

18 78 CHAPTER 4 SOLUTION STOICHIOMETRY 59. a. HBr: H, +1; Br, 1 b. HOBr: H, +1; O, 2; For Br, (2) + x = 0, x = +1 c. Br 2: Br, 0 d. HBrO 4: H, +1; O, 2; For Br, (2) + x = 0, x = +7 e. BrF 3: F, 1; For Br, x + 3(1) = 0, x = a. 3 b. 3 c. 2(x) + 4(+1) = 0, x = 2 d. +2 e. +1 f. +4 g. +3 h. +5 i To determine if the reaction is an oxidationreduction reaction, assign oxidation numbers. If the oxidation numbers change for some elements, the reaction is a redox reaction. If the oxidation numbers do not change, the reaction is not a redox reaction. In redox reactions, the species oxidized (called the reducing agent) shows an increase in oxidation numbers and the species reduced (called the oxidizing agent) shows a decrease in oxidation numbers. Redox? Oxidizing Reducing Substance Substance Agent Agent Oxidized Reduced a. Yes O 2 CH 4 CH 4 (C) O 2 (O) b. Yes HCl Zn Zn HCl (H) c. No d. Yes O 3 NO NO (N) O 3 (O) e. Yes H2O 2 H2O 2 H2O 2 (O) H2O 2 (O) f. Yes CuCl CuCl CuCl (Cu) CuCl (Cu) In c, no oxidation numbers change from reactants to products. 62. Redox? Oxidizing Reducing Substance Substance Agent Agent Oxidized Reduced a. Yes + Ag Cu Cu + Ag b. No c. No d. Yes SiCl 4 Mg Mg SiCl 4 (Si) e. No In b, c, and e, no oxidation numbers change.

19 CHAPTER 4 SOLUTION STOICHIOMETRY Use the method of halfreactions described in Section 4.10 of the text to balance these redox reactions. The first step always is to separate the reaction into the two halfreactions, then balance each halfreaction separately. 2 a. Zn Zn + 2 e 2e + 2 HCl H Cl 2 Adding the two balanced halfreactions, Zn(s) + 2 HCl(aq) H 2(g) + Zn (aq) + 2 Cl (aq) b. 3 I I 3 + 2e ClO Cl 2e + 2H + ClO Cl + H O 2 Adding the two balanced halfreactions so electrons cancel: 3 I (aq) + 2 H (aq) + ClO (aq) I 3(aq) + Cl (aq) + H2O(l) c. As2O 3 H3AsO 4 NO 3 NO + 2 H2O AsO H3AsO4 4 H + NO 3 NO + 2 H2O Left 3 O; Right 8 O (3 e + 4 H + NO 3 NO + 2 H2O) 4 Right hand side has 5 extra O. + Balance the oxygen atoms first using H2O, then balance H using H, and finally balance charge using electrons. (5 H2O + As2O 3 2 H3AsO H + 4 e ) 3 Common factor is a transfer of 12 e. Add halfreactions so electrons cancel. 12 e + 16 H + 4 NO 3 4 NO + 8 H2O 15 H O + 3 As O 6 H AsO + 12 H + 12 e H2O(l) + 4 H (aq) + 3 As2O 3(s) + 4 NO 3(aq) 4 NO(g) + 6 H3AsO 4(aq) d. (2 Br Br + 2 e ) 5 MnO Mn + 4 H O (5 e + 8 H + MnO Mn + 4 H O) Common factor is a transfer of 10 e. 10 Br 5 Br + 10 e 10 e + 16 H + 2 MnO 2 Mn + 8 H O H (aq) + 2 MnO 4(aq) + 10 Br (aq) 5 Br 2(l) + 2 Mn (aq) + 8 H2O(l) e. CH OH CH O Cr O Cr (CH OH CH O + 2 H + 2 e ) 3 14 H + Cr O 2 Cr + 7 H O 6 e + 14 H + Cr O 2 Cr + 7 H O Common factor is a transfer of 6 e.

20 80 CHAPTER 4 SOLUTION STOICHIOMETRY 3 CH OH 3 CH O + 6 H + 6 e 6 e + 14 H + Cr O 2 Cr + 7 H O H (aq) + 3 CH3OH(aq) + Cr2O 7 (aq) 2 Cr (aq) + 3 CH2O(aq) + 7 H2O(l) 64. a. (Cu Cu + 2 e ) 3 NO NO + 2 H O (3 e + 4 H + NO NO + 2 H O) Adding the two balanced halfreactions so electrons cancel: 2 3 Cu 3 Cu + 6 e 6 e + 8 H + 2 NO 2 NO + 4 H O Cu(s) + 8 H (aq) + 2 NO 3 (aq) 3 Cu (aq) + 2 NO(g) + 4 H2O(l) b. (2 Cl Cl + 2 e ) 3 Cr O 2 Cr + 7 H O 6 e + 14 H + Cr O 2 Cr + 7 H O Add the two halfreactions with six electrons transferred: 6 Cl 3 Cl + 6 e 6 e + 14 H + Cr O 2 Cr + 7 H O H (aq) + Cr2O 7 (aq) + 6 Cl (aq) 3 Cl 2(g) + 2 Cr (aq) + 7 H2O(l) c. Pb PbSO PbO PbSO Pb + H SO PbSO + 2 H PbO + H SO PbSO + 2 H O Pb + H SO PbSO + 2 H + 2 e e + 2 H + PbO 2 + H2SO 4 PbSO H2O Add the two halfreactions with two electrons transferred: + 2 e + 2 H + PbO + H SO PbSO + 2 H O Pb + H SO PbSO + 2 H + 2 e Pb(s) + 2 H2SO 4(aq) + PbO 2(s) 2 PbSO 4(s) + 2 H2O(l) This is the reaction that occurs in an automobile leadstorage battery. 2 d. Mn MnO 4 2 (4 H O + Mn MnO + 8 H + 5 e ) 2 2 4

21 CHAPTER 4 SOLUTION STOICHIOMETRY 81 NaBiO Bi + Na 6 H + NaBiO Bi + Na + 3 H O (2 e + 6 H + NaBiO Bi + Na + 3 H O) H O + 2 Mn 2 MnO + 16 H + 10 e 10 e + 30 H + 5 NaBiO 5 Bi + 5 Na + 15 H O Simplifying : H2O + 30 H + 2 Mn + 5 NaBiO 3 2 MnO Bi + 5 Na + 15 H2O + 16 H H (aq) + 2 Mn (aq) + 5 NaBiO 3(s) 2 MnO 4(aq) + 5 Bi (aq) + 5 Na (aq) + 7 H2O(l) 2 e. H3AsO 4 AsH 3 (Zn Zn + 2 e ) 4 H3AsO 4 AsH H2O + 8 e + 8 H + H AsO AsH + 4 H O e + 8 H + H3AsO 4 AsH H2O 2 4 Zn 4 Zn + 8 e H (aq) + H3AsO 4(aq) + 4 Zn(s) 4 Zn (aq) + AsH 3(g) + 4 H2O(l) 65. Use the same method as with acidic solutions. After the final balanced equation, convert H to OH + as described in section 4.10 of the text. The extra step involves converting H into H2O by adding equal moles of OH to each side of the reaction. This converts the reaction to a basic solution while keeping it balanced. a. Al Al(OH) MnO MnO 4 H O + Al Al(OH) + 4 H 3 e + 4 H + MnO MnO + 2 H O 4 H O + Al Al(OH) + 4 H + 3 e H O + Al Al(OH) + 4 H + 3 e 3 e + 4 H + MnO MnO + 2 H O H2O(l) + Al(s) + MnO 4(aq) Al(OH) 4(aq) + MnO 2(s) + Since H doesn t appear in the final balanced reaction, we are done. b. Cl Cl Cl OCl 2 e + Cl 2 Cl 2 H O + Cl 2 OCl + 4 H + 2 e e + Cl 2 Cl 2 H O + Cl 2 OCl + 4 H + 2 e H2O + 2 Cl 2 2 Cl + 2 OCl + 4 H Now convert to a basic solution. Add 4 OH to both sides of the equation. The 4 OH will react + with the 4 H on the product side to give 4 H O. After this step, cancel identical species on both 2

22 82 CHAPTER 4 SOLUTION STOICHIOMETRY sides (2 H2O). Applying these steps gives: 4 OH + 2 Cl 2 2 Cl + 2 OCl + 2 H2O, which can be further simplified to: 2 OH (aq) + Cl 2(g) Cl (aq) + OCl (aq) + H2O(l) c. NO NH Al AlO 6 e + 7 H + NO NH + 2 H O (2 H O + Al AlO + 4 H + 3 e ) Common factor is a transfer of 6 e. 6e + 7 H + NO NH + 2 H O H2O + 2 Al 2 AlO H + 6 e OH + 2 H2O + NO Al NH AlO 2 + H + OH Reducing gives: OH (aq) + H2O(l) + NO 2(aq) + 2 Al(s) NH 3(g) + 2 AlO 2(aq) 66. a. Cr Cr(OH) CrO Cr(OH) 3 H O + Cr Cr(OH) + 3 H + 3 e 3 e + 5 H + CrO Cr(OH) + H O H O + Cr Cr(OH) + 3 H + 3 e 3 e + 5 H + CrO Cr(OH) + H O OH + 2 H + 2 H2O + Cr + CrO 4 2 Cr(OH) OH Two OH were added above to each side to convert to a basic solution. The two OH react with + the 2 H on the reactant side to produce 2 H O. The overall balanced equation is: 2 4 H2O(l) + Cr(s) + CrO 4 (aq) 2 Cr(OH) 3(s) + 2 OH (aq) 2 b. S S MnO MnS (S S + 2 e ) 5 MnO + S MnS ( 5 e + 8 H + MnO + S MnS + 4 H O) Common factor is a transfer of 10 e. 2 5 S 5 S + 10 e 2 10 e + 16 H + 2 MnO + 2 S 2 MnS + 8 H O OH + 16 H + 7 S + 2 MnO 4 5 S + 2 MnS + 8 H2O + 16 OH 2 16 H2O + 7 S + 2 MnO 4 5 S + 2 MnS + 8 H2O + 16 OH 2 Reducing gives: 8 H2O(l) + 7 S (aq) + 2 MnO 4(aq) 5 S(s) + 2 MnS(s) + 16 OH (aq)

23 CHAPTER 4 SOLUTION STOICHIOMETRY 83 c. CN CNO (H O + CN CNO + 2 H + 2 e ) 3 2 MnO MnO (3 e + 4 H + MnO MnO + 2 H O) Common factor is a transfer of 6 electrons. 3 H O + 3 CN 3 CNO + 6 H + 6 e 6 e + 8 H + 2 MnO 2 MnO + 4 H O OH + 2 H + 3 CN + 2 MnO 4 3 CNO + 2 MnO 2 + H2O + 2 OH Reducing gives: H2O(l) + 3 CN (aq) + 2 MnO 4(aq) 3 CNO (aq) + 2 MnO 2(s) + 2 OH (aq) 67. NaCl + H2SO 4 + MnO 2 Na2SO 4 + MnCl 2 + Cl 2 + H2O We could balance this reaction by the halfreaction method or by inspection. Let s try inspection. To balance Cl, we need 4 NaCl: 4 NaCl + H2SO 4 + MnO 2 Na2SO 4 + MnCl 2 + Cl 2 + H2O + 2 Balance the Na and SO 4 ions next: 4 NaCl + 2 H2SO 4 + MnO 2 2 Na2SO 4 + MnCl 2 + Cl 2 + H2O On the left side: 4H and 10O; On the right side: 8O not counting H2O We need 2 H2O on the right side to balance H and O: 4 NaCl(aq) + 2 H2SO 4(aq) + MnO 2(s) 2 Na2SO 4(aq) + MnCl 2(aq) + Cl 2(g) + 2 H2O(l) 68. Au + HNO 3 + HCl AuCl 4 + NO Only deal with ions that are reacting (omit H ): Au + NO 3 + Cl AuCl 4 + NO The balanced halfreactions are: Au + 4 Cl AuCl + 3 e 3 e + 4 H + NO NO + 2 H O Adding the two balanced halfreactions: Au(s) + 4 Cl (aq) + 4 H (aq) + NO 3(aq) AuCl 4(aq) + NO(g) + 2 H2O(l)

24 84 CHAPTER 4 SOLUTION STOICHIOMETRY Additional Exercises g Ca = mol OH Molarity = 2 = M OH mol CaCl 2 present = L CaCl 2 = mol CaCl2 The volume of CaCl 2 solution after evaporation is: mol CaCl 2 = L = 57.5 ml CaCl2 Volume H2O evaporated = 230. ml 57.5 ml = 173 ml H2O evaporated 71. There are other possible correct choices for the following answers. We have listed only three possible reactants in each case. a. AgNO 3, Pb(NO 3) 2, and Hg 2(NO 3) 2 would form precipitates with the Cl ion. 2 Ag (aq) + Cl (aq) AgCl(s); Pb (aq) + 2 Cl (aq) PbCl 2(s); 2 Hg (aq) + 2 Cl (aq) Hg Cl (s) b. Na SO, Na CO, and Na PO would form precipitates with the Ca ion. Ca (aq) + SO (aq) CaSO (s); Ca + CO (aq) CaCO (s) 3 Ca (aq) + 2 PO (aq) Ca (PO ) (s) c. NaOH, Na S, and Na CO would form precipitates with the Fe ion. Fe (aq) + 3 OH (aq) Fe(OH) (s); 2 Fe (aq) + 3 S (aq) Fe S (s); 2 Fe (aq) + 3 CO (aq) Fe (CO ) (s) d. BaCl, Pb(NO ), and Ca(NO ) would form precipitates with the SO ion. Ba (aq) + SO (aq) BaSO (s); Pb (aq) + SO (aq) PbSO (s); Ca (aq) + SO (aq) CaSO 4(s) e. Na SO, NaCl, and NaI would form precipitates with the Hg ion. Hg (aq) + SO (aq) Hg SO (s); Hg (aq) + 2 Cl (aq) Hg Cl (s); Hg (aq) + 2 I (aq) Hg2I 2(s) f. NaBr, Na CrO, and Na PO would form precipitates with the Ag ion. Ag (aq) + Br (aq) AgBr(s); 2 Ag (aq) + CrO (aq) Ag CrO (s); 3 Ag (aq) + PO (aq) Ag PO (s) a. MgCl 2(aq) + 2 AgNO 3(aq) 2 AgCl(s) + Mg(NO 3) 2(aq)

25 CHAPTER 4 SOLUTION STOICHIOMETRY g AgCl = g MgCl = 14.2% MgCl 2 b g MgCl L = 18.8 g AgBr = 8.95 ml AgNO M2SO 4(aq) + CaCl 2(aq) CaSO 4(s) + 2 MCl(aq) g CaSO 4 = mol M2SO4 From the problem, 1.42 g M2SO 4 was reacted so: g M2SO 4 = mol M2SO 4, molar mass = = 142 g/mol 142 amu = 2(atomic mass M) (16.00), atomic mass M = 23 amu From periodic table, M = Na(sodium). 75. All the sulfur in BaSO 4 came from the saccharin. The conversion from BaSO 4 to saccharin utilizes the molar masses of each g BaSO 4 = g saccharin Avg. mass % = 100 = 67.00% saccharin by mass a. Fe (aq) + 3 OH (aq) Fe(OH) 3(s) Fe(OH) 3: (16.00) + 3(1.008) = g/mol g Fe(OH) 3 = g Fe b. Fe(NO 3) 3: (14.01) + 9(16.00) = g/mol

26 86 CHAPTER 4 SOLUTION STOICHIOMETRY g Fe = g Fe(NO 3) 3 c. Mass % Fe(NO 3) 3= 100 = 53.1% 77. Cr(NO 3) 3(aq) + 3 NaOH(aq) Cr(OH) 3(s) + 3 NaNO 3(aq) mol NaOH used = 2.06 g Cr(OH) 3 to form precipitate 2 = mol NaOH NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) mol NaOH used = L to react with HCl 2 = mol NaOH M NaOH = = 2.00 M NaOH 78. a. Perchloric acid reacted with potassium hydroxide is a possibility. HClO 4(aq) + KOH(aq) H2O(l) + KClO 4(aq) b. Nitric acid reacted with cesium hydroxide is a possibility. HNO 3(aq) + CsOH(aq) H2O(l) + CsNO 3(aq) c. Hydroiodic acid reacted with calcium hydroxide is a possibility. 2 HI(aq) + Ca(OH) 2(aq) 2 H2O(l) + CaI 2(aq) 79. HC2H3O 2(aq) + NaOH(aq) H2O(l) + NaC2H3O 2(aq) 3 3 a L soln = mol acetic acid Concentration of acetic acid = = M b. If we have L of solution: total mass = ml = 1006 g Mass of HC2H3O 2 = mol = g Mass % acetic acid = 100 = 5.010% 80. Mg(s) + 2 HCl(aq) MgCl 2(aq) + H 2(g) 3.00 g Mg = L = 49.4 ml HCl

27 CHAPTER 4 SOLUTION STOICHIOMETRY Let HA = unknown acid; HA(aq) + NaOH(aq) NaA(aq) + H2O(l) mol HA present = L = mol HA, x = molar mass of HA = 176 g/mol Empirical formula weight 3(12) + 4(1) + 3(16) = 88 g/mol Since 176/88 = 2.0, the molecular formula is (C3H4O 3) 2 = C6H8O a. Al(s) + 3 HCl(aq) AlCl 3(aq) + 3/2 H 2(g) or 2 Al(s) + 6 HCl(aq) 2 AlCl 3(aq) + 3 H 2(g) Hydrogen is reduced (goes from +1 oxidation state to 0 oxidation state) and aluminum Al is oxidized (0 +3). b. Balancing S is most complicated since sulfur is in both products. Balance C and H first then worry about S. CH 4(g) + 4 S(s) CS 2(l) + 2 H2S(g) Sulfur is reduced (0 2) and carbon is oxidized (4 +4). c. Balance C and H first, then balance O. C3H 8(g) + 5 O 2(g) 3 CO 2(g) + 4 H2O(l) Oxygen is reduced (0 2) and carbon is oxidized (8/3 +4). d. Although this reaction is mass balanced, it is not charge balanced. We need 2 mol of silver on each side to balance the charge Cu(s) + 2 Ag (aq) 2 Ag(s) + Cu (aq) Silver is reduced (+1 0) and copper is oxidized (0 +2) Mn + HNO 3 Mn + NO2 2 Mn Mn + 2 e HNO 3 NO2 HNO 3 NO 2 + H2O + (e + H + HNO NO + H O) Mn Mn + 2 e + 2 e + 2 H + 2 HNO 2 NO + 2 H O H (aq) + Mn(s) + 2 HNO 3(aq) Mn (aq) + 2 NO 2(g) + 2 H2O(l) 2 Mn + IO 4 MnO 4 + IO3

28 88 CHAPTER 4 SOLUTION STOICHIOMETRY 2 (4 H2O + Mn MnO H + 5 e ) 2 (2 e + 2 H + IO 4 IO 3 + H2O) 5 8 H O + 2 Mn 2 MnO + 16 H + 10 e e + 10 H + 5 IO 4 5 IO H2O H O(l) + 2 Mn (aq) + 5 IO (aq) 2 MnO (aq) + 5 IO (aq) + 6 H (aq) Challenge Problems 84. a. 5.0 ppb Hg in water = 8 = M Hg 9 b. = M CHCl 3 c ppm As = 4 = M As 7 d. = M DDT 85. a g AgCl = g Cl; %Cl = 100 = 29.7% Cl Cobalt(III) oxide, Co2O 3: 2(58.93) + 3(16.00) = g/mol g Co2O 3 = g Co; %Co = 100 = 24.8% Co The remainder, ( ) = 45.5%, is water. Assuming g of compound: 45.5 g H2O = 5.09 g H; %H = 100 = 5.09% H 45.5 g H2O = 40.4 g O; %O = 100 = 40.4% O The mass percent composition is 24.8% Co, 29.7% Cl, 5.09% H and 40.4% O. b. Out of g of compound, there are: 24.8 g Co = mol Co; 29.7 g Cl = mol Cl

29 CHAPTER 4 SOLUTION STOICHIOMETRY g H = 5.05 mol H; 40.4 g O = 2.53 mol O Dividing all results by 0.421, we get CoCl2 6H2O. c. CoCl2 6H2O(aq) + 2 AgNO 3(aq) 2 AgCl(s) + Co(NO 3) 2(aq) + 6 H2O(l) CoCl2 6H2O(aq) + 2 NaOH(aq) Co(OH) 2(s) + 2 NaCl(aq) + 6 H2O(l) Co(OH) 2 Co2O3 This is an oxidationreduction reaction. Thus, we also need to include an oxidizing agent. The obvious choice is O. 2 4 Co(OH) 2(s) + O 2(g) 2 Co2O 3(s) + 4 H2O(l) a. C12H10nCl n + n Ag n AgCl; molar mass (AgCl) = g/mol molar mass (PCB) = 12(12.01) + (10n) (1.008) + n(35.45) = n Since n mol AgCl are produced for every 1 mol PCB reacted, then n(143.4) grams of AgCl will be produced for every ( n) grams of PCB reacted. or mass ( n) = mass (143.4 n) AgCl PCB b ( n) = (143.4 n), n = n = n, n = a. 2 AgNO 3(aq) + K2CrO 4(aq) Ag2CrO 4(s) + 2 KNO 3(aq) Molar mass: g/mol g/mol g/mol The molar mass of Ag2CrO 4 is g/mol, so one mol of precipitate was formed. We have equal masses of AgNO 3 and K2CrO 4. Since the molar mass of AgNO 3 is less than that of K2CrO 4, then we have more mol of AgNO 3 present. However, we will not have twice the mol of AgNO 3 present as compared to K2CrO 4 as required by the balanced reaction; this is because the molar mass of AgNO 3 is no where near onehalf the molar mass of K2CrO 4. Therefore, AgNO is limiting. 3 mass AgNO 3 = mol Ag2CrO 4 = g AgNO3 Since equal masses of reactants are present, then g K2CrO 4 were present initially.

30 90 CHAPTER 4 SOLUTION STOICHIOMETRY = = M K + b. mol CrO = g K CrO = mol CrO present initially mol CrO in = mol Ag CrO = mol CrO precipitate = = M 88. Molar masses: KCl, = g/mol; KBr, = g/mol AgCl, = g/mol; AgBr, = g/mol Let x = number of moles of KCl in mixture and y = number of moles of KBr in mixture. Since Ag + Cl AgCl and Ag + Br AgBr, then x = moles AgCl and y = moles AgBr. Setting up two equations: g = x y and g = x y Multiply the first equation by, and subtract from the second = x y = x y = 25.7 x, x = mol KCl mol KCl = g KCl % KCl = 100 = 77.1%, % KBr = = 22.9% g BaSO 4 = g SO 4 ; % sulfate = = 60.0% Assume we have g of the mixture of Na2SO 4 and K2SO 4. There are: g SO 4 = mol SO4 2 There must be = 1.25 mol of +1 cations to balance the 2 charge of SO 4.

31 CHAPTER 4 SOLUTION STOICHIOMETRY Let x = number of moles of K and y = number of moles of Na ; then x + y = The total mass of Na and K must be 40.0 g in the assumed g of mixture. Setting up an equation: + + x mol K + y mol Na = 40.0 g So, we have two equations with two unknowns: x + y = 1.25 and x y = 40.0 Since x = 1.25 y, then 39.10(1.25 y) y = y y = 40.0, y = y = 0.55 mol Na and x = = 0.70 mol K Therefore: mol K = 0.35 mol K2SO 4; 0.35 mol K2SO 4 = 61 g K2SO4 Since we assumed g, the mixture is 61% K2SO 4 and 39% Na2SO a. H3PO 4(aq) + 3 NaOH(aq) 3 H2O(l) + Na3PO 4(aq) b. 3 H2SO 4(aq) + 2 Al(OH) 3(s) 6 H2O(l) + Al 2(SO 4) 3(aq) c. H2Se(aq) + Ba(OH) 2(aq) 2 H2O(l) + BaSe(s) d. H2C2O 4(aq) + 2 NaOH(aq) 2 H2O(l) + Na2C2O 4(aq) H3PO 4(aq) + 3 Ba(OH) 2(aq) 6 H2O(l) + Ba 3(PO 4) 2(s) L = L = 57.6 ml Ba(OH) ml NaOH = mol H2SO4 Molarity = = 3.72 M HSO a. MgO(s) + 2 HCl(aq) MgCl 2(aq) + H2O(l) Mg(OH) 2(s) + 2 HCl(aq) MgCl 2(aq) + 2 H2O(l) Al(OH) 3(s) + 3 HCl(aq) AlCl 3(aq) + 3 H2O(l)

32 92 CHAPTER 4 SOLUTION STOICHIOMETRY b. Let's calculate the number of moles of HCl neutralized per gram of substance. We can get these directly from the balanced equations and the molar masses of the substances. Therefore, one gram of magnesium oxide would neutralize the most 0.10 M HCl. 94. We get the empirical formula from the elemental analysis. Out of g carminic acid there are: g C = mol C; 4.09 g H = 4.06 mol H g O = mol O Dividing the moles by the smallest number gives: These numbers don t give obvious mol ratios. Let s determine the mol C to mol H ratio. = 1.10 = So let's try = as a common factor: = 11.0; = 10.0; = 6.50 Therefore, C22H20O 13 is the empirical formula. We can get molar mass from the titration data L soln = mol carminic acid Molar mass = The empirical formula mass of C22H20O 13 22(12) + 20(1) + 13(16) = 492 g. Therefore, the molecular formula of carminic acid is also C22H20O mol C6H8O 7 = g C6H8O 7 = mol C6H8O7

33 CHAPTER 4 SOLUTION STOICHIOMETRY 93 Let HxA represent citric acid where x is the number of acidic hydrogens. The balanced neutralization reaction is: x HxA(aq) + x OH (aq) x H2O(l) + A (aq) mol OH reacted = L = mol OH 3 x = = 3.01 Therefore, the general acid formula for citric acid is H3A, meaning that citric acid has three acidic hydrogens per citric acid molecule (citric acid is a triprotic acid). 96. a. HCl(aq) dissociates to H (aq) + Cl (aq). For simplicity let's use H and Cl separately. H H Fe HFeCl (2 H + 2 e H ) 3 (H + 4 Cl + Fe HFeCl + 3 e ) H + 6 e 3 H 2 2 H + 8 Cl + 2 Fe 2 HFeCl + 6 e 8 H + 8 Cl + 2 Fe 2 HFeCl H2 4 or 8 HCl(aq) + 2 Fe(s) 2 HFeCl (aq) + 3 H (g) 4 2 b. IO I I I 3 IO I (3 I I + 2 e ) IO 3 I H2O e + 18 H + 3 IO I + 9 H O 16 e + 18 H + 3 IO I + 9 H O I 8 I e 18 H + 24 I + 3 IO 3 9 I H2O Reducing: 6 H (aq) + 8 I (aq) + IO 3(aq) 3 I 3(aq) + 3 H2O(l) 4 3+ c. (Ce + e Ce ) Cr(NCS) 6 Cr + NO 3 + CO 2 + SO H2O + Cr(NCS) 6 Cr + 6 NO CO SO H Charge on left 4. Charge on right = (1) + 6(2) + 108(+1) = +93. Add 97 e to the right, then add the two balanced halfreactions with a common factor of 97 e transferred.

34 94 CHAPTER 4 SOLUTION STOICHIOMETRY H2O + Cr(NCS) 6 Cr + 6 NO CO SO H + 97 e e + 97 Ce 97 Ce Ce (aq) + 54 H2O(l) + Cr(NCS) 6 (aq) 97 Ce (aq) + Cr (aq) + 6 NO 3(aq) + 6 CO 2(g) SO 4 (aq) H (aq) This is very complicated. A check of the net charge is a good check to see if the equation is balanced. Left: charge = 97(+4) 4 = Right: charge = 97(+3) (1) + 6(2) + 108(+1) = d. CrI CrO + IO Cl Cl (16 H O + CrI CrO + 3 IO + 32 H + 27 e ) 2 (2 e + Cl 2 Cl ) Common factor is a transfer of 54 e. 54 e + 27 Cl 54 Cl 32 H O + 2 CrI 2 CrO + 6 IO + 64 H + 54 e H2O + 2 CrI Cl 2 54 Cl + 2 CrO IO H + Add 64 OH to both sides and convert 64 H into 64 H2O OH + 32 H2O + 2 CrI Cl 2 54 Cl + 2 CrO IO H2O Reducing gives: 2 64 OH (aq) + 2 CrI 3(s) + 27 Cl 2(g) 54 Cl (aq) + 2 CrO 4 (aq) + 6 IO 4(aq) + 32 H2O(l) 4+ e. Ce Ce(OH) (e + 3 H O + Ce Ce(OH) + 3 H ) Fe(CN) Fe(OH) + CO + NO Fe(CN) Fe(OH) + 6 CO + 6 NO There are 39 extra O atoms on right. Add 39 H2O to left, then add 75 H to right to balance H. 39 H O + Fe(CN) Fe(OH) + 6 CO + 6 NO + 75 H net charge = 4 net charge = Add 61 e to the right; then add the two balanced halfreactions with a common factor of 61 e transferred.

35 CHAPTER 4 SOLUTION STOICHIOMETRY H O + Fe(CN) Fe(OH) + 6 CO + 6 NO + 75 H + 61 e 61 e H O + 61 Ce 61 Ce(OH) H H2O + Fe(CN) Ce 61 Ce(OH) 3 + Fe(OH) CO NO H Adding 258 OH to each side then reducing gives: OH (aq) + Fe(CN) 6 (aq) + 61 Ce (aq) 61 Ce(OH) 3(s) + Fe(OH) 3(s) CO 3 (aq) + 6 NO 3(aq) + 36 H2O(l) f. Fe(OH) Fe(OH) H O HO (H O + Fe(OH) Fe(OH) + H + e ) 2 2 e + 2 H + H O 2 H O H O + 2 Fe(OH) 2 Fe(OH) + 2 H + 2 e 2 e + 2 H + H O 2 H O H2O + 2 H + 2 Fe(OH) 2 + H2O 2 2 Fe(OH) H2O + 2 H Reducing gives: 2 Fe(OH) 2(s) + H2O 2(aq) 2 Fe(OH) 3(s) The amount of KHP used = g = mol KHP Since one mole of NaOH reacts completely with one mole of KHP, the NaOH solution contains mol NaOH. Molarity of NaOH = Maximum molarity = Minimum molarity = We can express this as ± M. An alternative is to express the molarity as ± M. The second way shows the actual number of significant figures in the molarity. The advantage of the first method is that it shows that we made all of our individual measurements to four significant figures.

36 96 CHAPTER 4 SOLUTION STOICHIOMETRY