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RRERA 1 1 nd Ó! RT. E ass added. factor. SUMMARY 4.1 The quantitative uses of chemical reactions are based on the interpretation of stoichiometric coefficients as moles of reacting substance. In stoichiometry calcula- tions, the general strategy is to convert from the data to moles of reactants or products, then use the reaction stoichiometry (from the balanced chemical equation) to convert the moles of one substance to moies of another, and finally to convert the moles to the property of inter- est. The theoretical yield is the yield expected on the basis of the chemical equation. However, other reactions taking place may reduce the actual yield below the theo- retical yield, and the ratio of actual yield to theoretical yield is reported as the percentage yield. 4.2 and 4.3 The limiting reactant is the reactant that governs the theoretical amount of product that can be formed in a given reaction. The technique of combus- tion analysis, for the determination of empirical formu- las, especially of organic compounds, is based om the principle of limiting reactants. 4.4 The link between volumes of solution and moles of solute 1s the molar concentration (or mularity), the num- ber of moles of solute per liter of solution. Solutions are very useful in chemistry, parily because, through dilu- CLASSIFIED EXERCISES Mole Calculutions 6.1) (a) How many moles of H» are needed to convert 5,0 mol of O to water? (b) Determine the amount (in moles) of Hy needed to convert 5.0 mol of Os to hydro- gen peroxide, Ho0s. (42 (a) Calculate the number of moles of product gases produced from the explosion of 2.0 mol TNT by the reaction 4€,H506Ns(s) + 2109) — 28CO»(g) + 6No(g) + 10H50(g) The solution becomes purple immediately after the point is reached, when an excess of permanganate titi We can use the same type of calculations for both redox and acid-base titrations. In both cases the stoichiometric coefficients the chemical equation are used to derive the appropriate conversion CHAPTER tion (the reduction of concentration), we can transfer very small amounts of solute. A convenient procedure for reporting the hydrogen ion concentration in solu- tions is to give the pH of the solution (the negative lc g2= rithm of the molar concentration of Hº ions). 4.5 The volume of one solution needed «o react with a stated volume of another solution is obtained by convert- ing each volume to moles of solute and relatir g the sol- utes by using the reaction stoichioraetry as a conversion factor. 4.6 The compositions of mixtures, solutions, and com- pounds may be determined by volumetric analysis, of which the most important technique is the titration of an analyte with a titrant. The normal procedure is to mea- sure one solution into another until the stoichiometric point (the equivalence point) is reached. At the stoichio- metric point, enough titrant has been added to react with all the analyte. The stoichiometric point is shown by a color change either of the reagents or of an added indicater. In acid-base titrations, an acid reacts with a base. In redox titrations, an oxidizing agent reacts with a reducing agent “(BJ Calculate the number of moles of product gases pro- duced from the detonation of 3.2 mol of nitroglycerin molecules by the reaction 4C3H5O9Na(l) —» 12C04(g) + 6No(g) + Os(g) + 10H,0(g) 4.3 (a) In the commercial manufacture of nitric acid, how many moles of NO, produce 7.33 mol of HNOs in thg reaction 3NOs(g) + HoO(1) > 2HNOs(ag) + NO(g)? ( (b)JThe concentration of iodide ions in a solution can be determined by its oxidation to iodine with permanga- nate ion according to the reaction 2MnOy (ag) + 16H*(e9) + 101-(aq) > 2Mn?*(aq) + 5Is(ag) + 8HyO(1). 4 REACTION STOICHIOME Scanned by CamScanner 
