7.4 SOLUTION STOICHIOMETRY

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1 P = nrt O = nrt P 8.4 kpa L m mol mol K 94.6 kpa ml = 0.57 L 94 K 0.88 mol HO O L H O L H O mol O mol HO 8.4 kpa O L O mol O K O 94 K O 94.6 kpa O 0.57 L O Accding to the ideal gas law, the volume of oxygen at room pressure and temperature is predicted to be 0.57 L. Evaluation Accding to the evidence, the volume of oxygen gas produced at room conditions is 556 ml = L L L 0.0 % difference = = % L The prediction is judged to be verified since evidence agrees well with the predicted value, within %. The ideal gas law is judged to be verified by this investigation, since the evidence agrees well with the prediction. 9. [Typical responses:] One consumer reaction that produces and consumes gases is the burning of propane in an outdo barbecue. The reaction is: C H 8 (g) + 5 O (g) CO (g) + 4 H O(g) One industrial reaction that consumes a gas is the production of ammonium sulfate fertilizer. The reaction is: NH (g) + H SO 4 (aq) (NH 4 ) SO 4 (s) One labaty reaction that produces and consumes gases is the burning of methane (natural gas) in a lab burner. The reaction is: CH 4 (g) + O (g) CO (g) + H O(g) 7.4 SOLUTION STOICHIOMETRY Investigation 7.4: Analysis of Silver Nitrate (Demonstration) (Pages 00, 07) Purpose The purpose of this investigation is to use the stoichiometric method to find an unknown amount concentration. Problem What is the amount concentration of silver nitrate in solution? Copyright 007 Thomson Nelson Unit 4 Solutions Manual 9

2 Evidence mass of filter paper =.7 g mass of filter paper and precipitate =. g volume of silver nitrate solution = 00 ml Analysis mass of Ag(s) produced = (..7) g = 0.85 g AgNO (aq) Cu(s) Cu(NO ) (aq) Ag(s) 00 ml excess 0.85 g mol nag 0.85 g g mol nagno mol mol AgNO AgNO n AgNO AgNO mol 0.00 L mol/l mol Ag 0.85 g Ag g Ag mol/l AgNO mol AgNO mol Ag 0.00 L AgNO Evaluation [Students should be given the actual concentrations of their samples in der to properly evaluate their Investigation. F example:] The design of this investigation is judged to be adequate because it is simple and straightfward and allows f the problem to be answered easily. There are no obvious flaws, and it seems to be the best design available. The materials are of good quality. The procedure is judged adequate, as it wks very well and is easy to follow. The technological skills required are adequate; they are simple and direct. On the basis of my evaluation, I am very certain of my evidence. The only obvious sources of err might be from failure to wash the product thoughly to dry it properly befe measuring its mass. Given a repted concentration of the prepared AgNO (aq) of 0.80 mol/l: 0.79 mol/l mol/l 0.0 % difference = = % 0.80 mol/l 0.80 This investigation produced a very small % difference, indicating that it is very acceptable f accomplishing the purpose. Practice (Page 0). H SO 4 (aq) + NH (aq) (NH 4 ) SO 4 (aq) 50.0 ml 4.4 ml c.0 mol/l 0 Unit 4 Solutions Manual Copyright 007 Thomson Nelson

3 n NH = 4.4 m L.0 mol L = 5.7 mmol nhso = 5.7 mmol 4 = 6.8 mmol 6.8 m mol chso = ml = 0.57 mol/l.0 mol NH chso = 4.4 m L NH mol HSO4 4 L NH mol NH 50.0 ml H SO 0.57 mol/l HSO4. Ca(OH) (aq) + Al (SO 4 ) (aq) CaSO 4 (s) + Al(OH) (s) 5.0 ml mol/l 0.5 mol/l 0.5 mol n Al (SO 4 ) = 5.0 m L L =. mmol nca(oh) =. mmol = 9.8 mmol L Ca(OH) = 9.8 m mol mol = 75 ml = 5 m L Al (SO ) Ca(OH) mol Al (SO 4) L Al (SO ) 4 75 ml Ca(OH). FeCl (aq) Na CO (aq) 6 NaCl(aq) Fe (CO ) (s) 75.0 ml excess 0.00 mol/l 0.50 mol/l 0.00 mol nfecl 75.0 m L L 5.0 mmol nnaco 5.0 mmol.5 mmol L NaCO.5 m mol 0.50 mol 90.0 ml 4 mol Ca(OH) mol Al (SO 4) L Ca(OH) 0.05 mol Ca(OH) Copyright 007 Thomson Nelson Unit 4 Solutions Manual

4 Na CO = 75.0 m L FeCl 90.0 ml NaCO 0.00 mol FeCl L FeCl mol Na CO mol FeCl L Na CO 0.50 mol Na CO Lab Exercise 7.C: Testing Solution Stoichiometry (Page 0) Purpose The purpose of this exercise is to test the stoichiometric method using solutions. Problem What mass of precipitate is produced by the reaction of 0.0 ml of 0.0 mol/l sodium sulfide with an excess quantity of aluminium nitrate solution? Prediction Accding to the stoichiometric method, 0 mg of precipitate is produced by the reaction of 0.0 ml of 0.0 mol/l sodium sulfide with excess aluminium nitrate solution. This prediction is based on the following calculation: Na S(aq) + Al(NO ) (aq) Al S (s) + 6 NaNO (aq) 0.0 ml m 0.0 mol/l 50.7 g/mol n NaS = 0.0 m L n m m Al S Al S = 4.0 mmol = 4.0 mmol =.40 mmol =.40 m mol 0.0 mol L = 0 mg 0.0 g = L Na S Al S 0.0 g AlS 50.7 g mol 0.0 mol Na S L Na S mol AlS mol Na S Analysis mass of precipitate =.7 g 0.97 g = 0.0 g Accding to the evidence collected, 0.0 g of precipitate was produced g Al S mol Al S Evaluation The design is judged to be adequate because the problem can be answered with no apparent flaws. There does not appear to be a better design that can be used to answer the problem. The positive test f excess aluminium nitrate gives me confidence in this design. Uncertainty of the accuracy of the measuring instruments and possible uncertainties in the procedure of washing and drying the precipitate would probably affect the results by about 5%. On the basis of the evaluation of this experiment, I am very certain of the results. Unit 4 Solutions Manual Copyright 007 Thomson Nelson

5 0.0 g 0.0 g 0.0 % difference = 00 = 00 = 5% 0.0 g 0.0 The percent difference is 5%, not me than the estimated uncertainty. Since the predicted answer closely agrees with the experimental answer and the difference can be accounted f by the uncertainties mentioned, the prediction is judged to be verified. The method of stoichiometry used in this experiment is acceptable because the prediction was verified. I am very certain of this judgment. The purpose was clearly accomplished f this example. Testing other chemical reactions would be useful to better achieve the purpose. Lab Exercise 7.D: Determining a Solution Concentration (Page 0) Purpose The purpose of this exercise is to use the stoichiometric method with solutions. Problem What is the amount concentration of silver nitrate in the solution to be recycled? Design A sample of silver nitrate solution to be recycled reacts with an excess quantity of sodium sulfate in solution. The precipitate fmed is filtered and the mass of the dried precipitate is measured. Analysis mass of Ag SO 4 (s) = (6.74.7) g = 5.47 g AgNO (aq) + Na SO 4 (aq) Ag SO 4 (s) + NaNO (aq) 00 ml 5.47 g c.8 g/mol n AgSO = 5.47 g mol 4.8 g = mol nagno = mol = 0.05 mol 0.05 mol AgNO = 0.00 L = 0.5 mol/l mol Ag SO4 mol AgNO AgNO = 5.47 g AgSO4.8 g AgSO4 mol Ag SO L AgNO 0.5 mol/l AgNO Accding to the evidence and the stoichiometric method, the amount concentration of silver nitrate solution is 0.5 mol/l. Section 7.4 Questions (Page 0). HCl(aq) + Al(OH) (s) AlCl (aq) + H O(l) 9 mg 0.0 mol/l 78.0 g/mol Copyright 007 Thomson Nelson Unit 4 Solutions Manual

6 n Al(OH) = 9 m g n HCl HCl =.7 mmol =.7 mmol = 5. mmol = 5. m mol mol 78.0 g L 0.0 mol =.5 0 ml 0.5 L HCl = 0.9 g Al(OH) mol Al(OH) mol HCl 78.0 g Al(OH) mol Al(OH) 0.5 L HCl. SO (g) + H O(l) H SO 4 (aq) 0.0 Mg 7.00 kl g/mol c n SO = 0.0 M g mol g = 0.5 Mmol nhso = 0.5 Mmol 4 = 0.5 Mmol 5 kmol 5 k mol HSO 4 = 7.00 k L = 7.8 mol/l 4 H SO = 0.0 M g SO mol SO g SO mol H SO mol SO mol/l HSO4. KOH(aq) + H SO 4 (aq) K SO 4 (aq) + HOH(l) 9.44 ml 0.00 ml 50.6 mmol/l c n KOH = 9.44 m L n HSO 4 = 478 mol = 478 mol = 9 mol 50.6 mmol L L HCl 0.0 mol HCl 7.00 k L HSO4 000 k L HSO4 M L HSO4 4 Unit 4 Solutions Manual Copyright 007 Thomson Nelson

7 9 mol HSO 4 = 0.00 ml =.9 mmol/l 50.6 m mol KOH mol HSO4 HSO 4 = 9.44 m L KOH L KOH mol KOH 0.00 m L HSO4.9 mmol/l HSO4 4. (a) A ph test of the filtrate with a ph meter a suitable indicat will show an excess of sodium hydroxide if the filtrate solution tests basic. (b) AgNO (aq) + NaOH(aq) AgOH(s) + NaNO (aq) 0.00 ml m mol/l 4.88 g/mol n AgNO = 0.00 m L mol L = 5.00 mmol nagoh = 5.00 mmol = 5.00 mmol m 4.88 g AgOH = 5.00 m mol mol = 64 mg 0.64 g mol AgNO magoh = 0.00 m L AgNO mol AgOH 4.88 g AgOH L AgNO mol AgNO mol AgOH 64 mg AgOH 0.6 g (c) % yield = 00 = 98.0% 0.64 g The purity of the solution is relatively high. 6 HCl(aq) Fe O (s) FeCl (aq) H O(l) 0.0 L g/mol.0 mol/l.0 mol nhcl 0.0 L L 4.0 mol nfeo 4.0 mol mol g mfeo 4.00 mol mol 69 g 5. Copyright 007 Thomson Nelson Unit 4 Solutions Manual 5

8 m FeO = 0.0 L HCl.0 mol HCl L HCl mol FeO g FeO 6 mol HCl mol Fe O 69 g FeO 6. Problem What is the amount concentration of a sodium sulfate solution? Design An excess quantity of a calcium nitrate solution is added to a known volume of the sodium sulfate solution and the resulting precipitate is dried, its mass determined, and the chemical amount of precipitate fmed is calculated. Using the balanced chemical equation and volumetric stoichiometry techniques, the concentration of the sodium sulfate solution is determined. Materials lab apron eye protection graduated cylinder 50 ml beaker filter paper centigram balance stirring rod wash bottle of pure water (deionized distilled) small funnel Extension 7. (a) Uses of soda ash include glass manufacturing, cleaning air and softening water, removing sulfur dioxide and hydrochlic acid from stack gases, and in the chemical production of soft drink sweeteners, sodium bicarbonate, phosphates (used in food and toiletries), and household detergents and paper products. (b) Two raw materials of the Solvay process are ammonia and carbon dioxide, and two final products are ammonium chlide and sodium hydrogen carbonate. (c) The Solvay process is an industrial-scale technology. (d) The Solvay process offered many advantages over the LeBlanc process. First, the LeBlanc process was much me expensive than the Solvay process. Second, the LeBlanc process involved burning coal, which produced a lot of air pollution. The Solvay process, on the other hand, produces no by-products, only the desired product. As industrialization progressed, the cleanliness of the Solvay process became me attractive. Finally, from a technological point of view, the Solvay process is much me efficient and reliable. Chapter 7 SUMMARY Make a Summary (Page 08) m *. (a) n (one measurement required) M v * n (one measurement required) n C* v* (two measurements required) * indicates measured quantities 6 Unit 4 Solutions Manual Copyright 007 Thomson Nelson