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Aqueous-solution Reactions

Aqueous-solution Reactions. Classify a reaction by Homogeneous chemical reactions: gas phase solutions aqueous-solution (common occurrence) non-aqueous-solution Heterogeneous (more than one phase ) chemical reactions: gas / liquid gas / solid liquid / solid.

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Aqueous-solution Reactions

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  1. Aqueous-solution Reactions Classify a reaction by Homogeneous chemical reactions: gas phase solutions aqueous-solution (common occurrence) non-aqueous-solution Heterogeneous (more than one phase) chemical reactions: gas / liquid gas / solid liquid / solid aqueous solution reactions Know the meaning of terms

  2. Nature of Aqueous Solutions Nature of compounds molecular substances (polar, non-polar, H-bonding) non-electrolytes ionic substances (acids, bases, salts)strong electrolytes (completely ionized in solution)week electrolytes (not completely ionized in solution) Know your terms and species (in the solution) aqueous solution reactions

  3. Dissolving a Strong Electrolyte See them in your imagination aqueous solution reactions

  4. aqueous solution reactions

  5. Strong Electrolytes Strong acids: HNO3, H2SO4, HCl, HClO4 Strong bases: MOH (M = Na, K, Cs, Rb etc) Salts: All salts dissolving in water are completely ionized. The ions may react with water (to be discussed in Chem 123) Stoichiometry & concentration relationship NaCl (s)  Na+ (aq) + Cl– (aq) Ca(OH)2 (s) Ca+(aq) + 2 OH– (aq) AlCl3 (s)  Al3+ (aq) + 3 Cl– (aq) (NH4)2SO4 (s)  2 NH4+ (aq) + SO42– (aq) aqueous solution reactions

  6. Concentration of Ions A bottle labeled as 0.100 M Al2(SO4)3. [Al3+] = _____ M (mol / L) [SO42–] = _____ M Assume sea water is 0.438 M NaCl, 0.0512 M MgCl2, and 0.001 M CaCl2 [Na+] = _____ M [Mg2+] = _____ M [Ca2+] = _____ M [Cl–] = _____ M Know how to calculate your quantities aqueous solution reactions

  7. Precipitations When ions form a solid that is not very soluble, a solid is formed. Such a phenomenon is called precipitation. The formation of a precipitation is also an equilibrium phenomenon (a subject to be covered in Chem123) Ag+ (aq) + Cl– (aq)  AgCl(s)or AgCl(s)  Ag+ (aq) + Cl– (aq) Ksp = [Ag+][Cl–] is a constant the solubility product aqueous solution reactions

  8. Precipitation Reactions Heterogeneous Reactions Spectator ions or bystander ions Ag+ (aq) + NO3– (aq) + Cs+ (aq) + I– (aq)  AgI (s) + NO3– (aq) + Cs+ (aq) Ag+ (aq) + I– (aq)  AgI (s) (net reaction)or Ag+ + I– AgI (s) Mostly insoluble Silver halidesMetal sulfides, hydroxidescarbonates, phosphates Soluble ions Alkali metals, NH4+nitrates, ClO4-, acetate Mostly soluble ions Halides, sulfates aqueous solution reactions

  9. Acid-base Reactions HCl (g)  H+ (aq) + Cl– (aq) NaOH (s)  Na+ (aq) + OH– (aq) neutralization reaction: H+ (aq) + OH– (aq) H2O (l) Explain these reactions Mg(OH)2 (s) + 2 H+ Mg2+ (aq) + 2 H2O (l) CaCO3 (s) + 2 H+ Ca2+ (aq) + H2O (l) + CO2 (g) Mg(OH)2 (s) + 2 HC2H3O2  Mg2+ (aq) + 2 H2O (l) + 2 C2H3O2 – (aq) acetic acid aqueous solution reactions

  10. Oxidation-reduction reactions Oxidation reaction must be accompanied by reductions – redox reactions Increasing oxidation state is oxidation (loss e–, LEO)Decreasing oxidation state is reduction (gain e–, GER) What elements are oxidized and reduced in each reaction? Work out the oxidation state changes for them as well! 2 KClO3 2 KCl + 3 O2 Fe2O3 + 3 CO  2 Fe + 3 CO2 MnO2 + 4 H+ + 2 Cl– Mn2+ + 2 H2O + Cl2 aqueous solution reactions

  11. Review Oxidation States Oxidation states is an assigned number. Formal charge concept may be used to assign oxidation states. Work out the oxidation states of all elements in these species: NH3 N2H4 NH2OH N2 N2O NO NO2– NO2 NO3–Cl– Cl2 ClO– ClO2– ClO2 ClO2– ClO3– ClO4– CO H2C2O4 C2O42–C2H6 CH4 CO2 CO32– PH3 P4 H3PO4 PO43– H2S HS– S2– S6 SO2 SO3– SO3 S2O32– SO42– H2O2 MnO2 KMnO4 MnO4– K2CrO4 CrO4– K2Cr2O7 Cr2O7– Review stoichiometry aqueous solution reactions

  12. Half Reactions These reactions explained during the lecture: Zn = Zn2+ + 2 e– Cu2+ + 2 e– = Cunet (electron transfer) Zn (s) + Cu2+ (aq) = Zn2+ (aq) + Cu (s) For these half reactions, Zn = Zn2+ + 2 e– 2 H+ + 2 e– = H2get and explain the net reaction yourself aqueous solution reactions Explain how reactions proceed

  13. Balance Half Equations • Identify the key element that undergoes an oxidation state change. • Balance the number of atoms of the key element on both sides. • Add the appropriate number of electrons to compensate for the change of oxidation state. • Add H+ (in acid medium), or OH- (in basic medium), to balance the charge on both sides of the half-reactions; and H2O, if necessary, to balance the equations. Page 9 of handout Balance MnO4 – + ____ + _____ ® Mn2+ + __ H2O aqueous solution reactions

  14. Balance these half equations Zn (s) ® Zn2+(aq) Cu2+ (aq) ® Cu (s) H2(g) ® H+ (aq) I –(aq)® I2 Fe2+ (aq) ® Fe3+ (aq) SO32– (aq) ® SO42– (aq) 2 S2O32–(aq) ® S4O62–(aq) + 2e–1 Cr2O72–(aq) ® Cr3+ (aq) I will illustrate the balance of these half reaction equations and those equations in other slides during the lecture. If you are not at my lecture, you should practice their balance to acquire your skills. The textbook gives a slight different method to balance redox equations and please find out the difference. Both ways wok. You may use either method. aqueous solution reactions Work on these from time to time

  15. Balance Redox Reaction equations Add two half reaction equations so that you can cancel all electrons to obtain a balanced redox reaction equation H2O2 + I – ® I2 + H2O MnO4 – + H2O2® Mn2+ + O2 MnO4 – + SO3 2–® Mn2+ + SO42– MnO4 – + Fe2+® Mn2+ + Fe3+ Cr2O7 2– + UO2+® Cr3+ + UO22+ Work on these from time to time to refresh your skills. aqueous solution reactions

  16. Disproportionation Reactions Balance disproportionation reaction (the same substance is both oxidized and reduced) H2O2® 2 H2O + O2 S2O32–® SO42– + S (s) S2O32–® SO2 + S (s) aqueous solution reactions Work on these from time to time

  17. Analyze and Learn the Skills Analyze this example and learn the skills to help you overcome any difficulty. Task: Balance the equation: S2O32–® SO42– + S (s) Identify the element oxidized and reduced: oxidation states of S in S2O32– SO42– and S are +4, +6, and 0 respectively. S is both oxidized and reduced. The oxidation half reaction: S2O32– ® 2 SO42– + 8 e– (2 S from +2  +6, (2×4=8))The reduction half reaction: S2O32– + 4 e – (2S from +2  0, (2×2=4)) ® 2 S Balance the charge with H+ S2O32–® 2 SO42– + 8 e– + 10 H+ (both sides have 2-) S2O32– + 4 e – + 6 H+® 2 S (both sides have 0) Add water to balance: S2O32– + 5 H2O ® 2 SO42– + 8 e– + 10 H+ S2O32– + 4 e – + 6 H+® 2 S + 3 H2O Make # of e the same: S2O32– + 5 H2O ® 2 SO42– + 8 e– + 10 H+ 2 S2O32– + 8 e – + 12 H+® 4S + 6 H2O The balanced equation: 3 S2O32– + 2 H+® 2 SO42– + 4 S+ 10 H+ Make sure you fill in the details too much to be included here!!! aqueous solution reactions

  18. Balance Redox Reaction in Basic Solutions Redox reactions may have different products depends on the acidity (pH) of the solutions. In basic solutions, there are more OH– ions than H+ ions. Thus, it is sensible to have OH– appearing in the equations than to have H+ ions. Balance these reactions in a basic solution: MnO4 – + CN –® MnO2 + OCN – Any one of several ways to assign oxidation states for CN works. MnO4 – + SO32–® MnO2 + SO42– Practice balance these from time to time to polish you skills! aqueous solution reactions

  19. Oxidizing and Reducing Agents Oxidizing agent or oxidant such as O2 or F2 is a substance that is able to oxidize other substances. It is reduced in the process (gains electron or decreases oxidation state). Describereducing agent or reductant O x I d a n t R e d u c t a n t NH3 N2H4 NH2OH N2 N2O NO NO2 – NO2 NO3 – Species Cannot be oxidized further Species Cannot be reduced further aqueous solution reactions

  20. Titrations Titration is a method used in volumetric analysis. The addition of a solution is carefully controlled so that stoichiometric amounts can be read from a burette. Titration can be carried out for instantaneous or rapid reactions such as neutralization and oxidation reactions. Explain these terms: neutralization,titration,quivalence point, half equivalence point, indicators aqueous solution reactions

  21. Conductance in Titration Conductance measurement of a HCl solution titrated by NaOH is shown:measured (total) conductancearea due to the ions labeled Do all ions have the same conductance? Why or why not? Why does the total conductance vary? Is conductance of an ion depends on the concentration? conductance H+ OH– Na+ Cl– V of NaOH added aqueous solution reactions Explain physical properties of chemicals

  22. Stoichiometry in Solution Chemistry For titration calculations, the amount of reactant m is evaluated from the concentration C and volume V by m = C * V For example, when m1 amount of acid is neutralized by m2 amount of base, m1 = m1. For redox reactions, similar relationship can also be used, but the stoichiometric relationship should be kept in mind. Amount in mmol = C in M * V in mL aqueous solution reactions

  23. Volumetric Analysis A 5.00-mL sample of vinegar requires 38.08 mL of 0.1000 M NaOH solution to reach the equivalence point. What is the concentration of acetic acid in the vinegar by weight percent if its density is 1.01 g / mL? Solution: Net reaction: OH– + HC2H3O2  H2O + C2H3O2 – (aq) If you find this solution difficult to understand, use your own method to solve it 1 mL vinegar1.01 g vinegar 38.08 mL OH–5 mL vinegar 0.1000 mol1000 mL 1 mol HC2H3O2 1 mol OH– 60.05 g HC2H3O21 mol HC2H3O2 = 0.0453 HC2H3O2 in vinegar = 4.53 % HC2H3O2 in vinegar The vinegar has 4.53 % of acetic acid by mass. What’s the concentration of a 7% vinegar? aqueous solution reactions

  24. Another way of thinking A 5.00-mL sample of vinegar requires 38.08 mL of 0.1000 M NaOH solution to reach the equivalence point. What is the concentration of acetic acid in the vinegar by weight percent if its density is 1.01 g / mL?Solution:a slight variation and hope you find it easier to followNet reaction: OH– + HC2H3O2  H2O + C2H3O2 – (aq) 0.1000 mol1000 mL 1 mol HC2H3O2 1 mol OH– 60.05 g HC2H3O21 mol HC2H3O2 38.08 mL OH–5 mL vinegar 1.01 g vinegar1 mL vinegar Mass of acetic acid Mass of sample 4.53 % ofHC2H3O2 in vinegar = = 0.0453 HC2H3O2 in vinegar = 4.53 % HC2H3O2 in vinegar aqueous solution reactions What the concentration of a 7% vinegar?

  25. Chemical Analysis Application How much 0.1000 M KMnO4 solution is required to reach the equivalence point in a titration of 1.00 g oxidize oxalic acid (oa = H2C2O4.2H2O)? Solution: Redox reaction:2 MnO4– + 5 H2C2O4 + 6 H+ = 2 Mn2+ + 8 H2O + 10 CO2 (balanced? Chk pls) 1 mol oa 126 g oa 2 mol MnO4 5 mol oa 1000 mL 0.1000 mol 1.00 g oa = 31.75 mL MnO4– Molar mass of H2C2O4.2H2O = 126 g mol-1 Note mole ratio in the balanced equation. Do problem 5.97 aqueous solution reactions

  26. Back Titration A 1.00-g sample containing MnO2 dissolved in solution is treated with 2.00 g of oxalic acid (oa = H2C2O4.2H2O). Then 50.00 mL 0.1000 M KMnO4 is required for the titration of the excess oa. What is the % MnO2 by mass? Solution: Redox reaction:2 MnO4– + 5 H2C2O4 + 6 H+ = 2 Mn2+ + 8 H2O + 10 CO2 H2C2O4 + MnO2 + 2 H+ = Mn2+ + 2 H2O + 2 CO2 (balanced? Chk pls) 0.1000 mol MnO4 1000 mL 5 mol oa 2 mol MnO4 126 g oa 1 mol oa 50.00 mL MnO4 = 1.575 g oa 86.9 g MnO2 126 g oa 100 % 1.0 g Sample (2.000 - 1.575) g oa = 29.0 % MnO2 by mass Cool head 4 complicated problem, eh! aqueous solution reactions

  27. Review 1 Sufficient amount of AgNO3 is placed in a 10.00 mL of tab water, and the AgCl solid is filtered and dried. The solid weighs 0.123 g. What is the concentration of chloride ion? Solution:access and limiting reagent, and ppt 0.123 g AgCl 10.00 mL 1 mol AgCl143.4 g AgCl 1000 mL1 L 1 mol Cl-1 mol AgCl = 0.0858 mol / L of Cl– aqueous solution reactions Express [Cl-] in mol and mass %.

  28. Review 2 A 0.1234-g sample (S) NaCl and sugar mixture contains 40% NaCl. When dissolved in water, the solution is treated with AgNO3. How much dry AgCl is the theoretical yield? Solution:percentage analysis 40 g NaCl100 g S 143.4 g AgCl1 mol AgCl 1 mol AgCl58.5 g NaCl 0.1234 g S = 0.1323 g AgCl  theoretical yield aqueous solution reactions Use the factors to help you think!

  29. Review 3 A 0.2345-g sample (S) NaCl and CaCl2 mixture contains 40% NaCl. When dissolved in water, the solution is treated with AgNO3. How much dry AgCl is the theoretical yield? Solution: 143.4 g AgCl58.5 g NaCl 0.2345*0.40 g NaCl = 0.2299 g AgCl 2*143.4 g AgCl110 g CaCl2 = 0.3668 g AgCl 0.2345*0.60 g CaCl2 (0.2299 + 0.3668) g AgCl = 0.5967 g AgCl Solve the same for a mixture of NaCl and KCl. Find the percentage of NaCl if 0.5000 g AgCl is collected. aqueous solution reactions

  30. Review 4 When 0.2345-g NaCl and CaCl2 mixture is dissolved in water, the solution is treated with AgNO3. The mass of dry AgCl collected is 0.5967 g. What is the percentage of NaCl in the mixture? Solution: Assume the sample contains x fraction of NaCl 143.4 g AgCl58.5 g NaCl 0.2345 (x) g NaCl 2*143.4 g AgCl110 g CaCl2 + 0.2345 (1 – x) g CaCl2 = 0.5967 g AgCl Solve for x in the equation: x = 0.40 = 40% Solve the same problem for 0.6000 instead of 0.5967 g AgCl. In this problem, what are the min. and max. masses of AgCl? (0.5748 – 0.6114 g) aqueous solution reactions

  31. Review 5 - skills obtain empirical formula from composition and combustion experiment find molecular formula from empirical formula and molar mass evaluate theoretical yield in a reaction, identify the limiting reagent Identify limiting reagent and evaluation percent yield in a reaction predict amounts of products or reagents required in reactions find percent yield of a reaction but pay attention to limiting reagent give concentration of common ions in a solution of several salts calculate masses of reagents or products (AgCl) involving common ions find percentage of a compound in a mixture by titration or precipitation aqueous solution reactions

  32. Review 6 – skill 2 Identify oxidation states and recognize reagent oxidized balance redox reaction equations evaluate quantities of reagents or products involving redox reactions stoichiometry calculation in titration experiments paying attention to molar relationship such as H3PO4, Ca(OH)2, as well as redox reactions evaluate quantities involving isotope composition of elements calculate one of density, mass and volume in solid, liquid, and gas name inorganic compounds write proper net ionic equation of reaction (know your spectator ions) aqueous solution reactions

  33. TA Hours & Rooms – fall 03 The Tutors handle the tutorial periods for CHEM 120/121 but they can also provide assistance to individuals or small groups on a drop-in basis according to the following schedule. (i.e. One of the Tutors will be in each room for the specified period. You can drop in at any time during that period to get some help.) Day Time Room*Monday 12:30-1:20 PHY 313 Monday 1:30-2:20 MC 4062 Monday 2:30-3:20 PHY 150 Wednesday 12:30-3:20 PHY 313 Wednesday 1:30-2:20 MC 4060 * These rooms are for one-on-one tutorial, not tutors office. aqueous solution reactions

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