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Reactions in Aqueous Solution

Chapter 4 (semester 2/2013). Reactions in Aqueous Solution. 4.1 General Properties of Aqueous Solutions 4.2 Precipitation Reactions 4.3 Acid- Base Reactions 4.4 Oxidation – Reduction Reactions 4.5 Concentration of Solutions. prepared by A. Kyi Kyi Tin

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Reactions in Aqueous Solution

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  1. Chapter 4 (semester 2/2013) Reactions in Aqueous Solution 4.1 General Properties of Aqueous Solutions 4.2 Precipitation Reactions 4.3 Acid- Base Reactions 4.4 Oxidation – Reduction Reactions 4.5 Concentration of Solutions prepared by A. Kyi Kyi Tin Ref: Raymong Chang. Chemistry Eleventh Edition, McGraw – Hill International Edition

  2. Solution Solvent Solute 4.1 General Properties of Aqueous Solutions Solution = [ solute + solvent] [smaller amount + larger amount] [CLEAR, HOMOGENEOUS MIXTURE] Aqueous solution = solute (liquid “or” solid (gas)) + solvent (water) H2O Sea water Salt (NaCl) Air (g) N2 O2, Ar, CH4 Cu Ni Alloy 4.1

  3. nonelectrolyte strong electrolyte weak electrolyte Two types of Solutes Electrolyte When dissolved in water can conduct electricity Non-electrolyte When dissolved in water does not conduct electricity 100%dissociation/ One-sided reaction Incomplete dissociation/reversible Ref: Raymond Chang Chemistry, Ninth Edition Figure 4.1, Page 120 4.2

  4. H2O NaCl (s)Na+ (aq) + Cl- (aq) CH3COOHCH3COO- (aq) + H+ (aq) Conduct electricity in solution? Dissociation means breaking up into..Cations (+)and Anions (-) Strong Electrolyte – 100% dissociation Weak Electrolyte – not completely dissociated Note: Pure water contains very few ions, can conduct electricity slightly (extremely weak electrolyte) 4.3

  5. Hydration: is the process in which an ion is surrounded by water molecules arranged in a specific manner. Water, electrically neutral molecule has a positive poles and negative poles, it is a polar solvent. Ex: when NaCl dissolves in water Na+ ions and Cl- ions are separated from each other and undergo “hydration”. Hydration helps to stabilize ions in solution and prevents cations from combining with anions. 4.4

  6. A reversible reaction. The reaction can occur in both directions. Ionization of acetic acid CH3COOHCH3COO- (aq) + H+ (aq) Acetic acid is a weak electrolyte because its ionization in water is incomplete. 4.5

  7. H2O C6H12O6 (s) C6H12O6 (aq) Nonelectrolyte does not conduct electricity? No cations (+) and anions (-) in solution Ref: Raymond Chang Chemistry, Ninth Edition Page 121 4.6

  8. precipitate Pb(NO3)2(aq) + 2NaI (aq) PbI2(s) + 2NaNO3(aq) Pb2+ + 2NO3- + 2Na+ + 2I- PbI2 (s) + 2Na+ + 2NO3- Pb2+ + 2I- PbI2 (s) 4.2Precipitation Reactions (Metathesis reaction) or (Double Displacement reaction) One product is insoluble solid molecular equation ionic equation net ionic equation Na+ and NO3- are spectator ions 4.7

  9. Solubility: Maximum amount of solute that will dissolve in a given quantity of solvent in a specific temperature. soluble Substances: Slightly soluble insoluble Soluble : fair amount is visibly dissolves when added to water • All ionic compounds are strong electrolytes, but they are not equally soluble. • Even insoluble compounds dissolve to a certain extent • Examples are: (NH4)2CO3, (NH4)3PO4,(NH4)2S,(NH4)2CrO4 4.8

  10. 4.3 Acid-Base Reactions ACID: Arrhenius acid is a substance that produces H+ (H3O+) in water BASE: Arrhenius base is a substance that produces OH- in water Ref: Raymond Chang Chemistry, Ninth Edition Figure 4.7,4.8 Page 128,129 4.9

  11. Electrostatic potential map of the Hydronium ion, hydrated proton, H3O+ the most electron- rich region the most electron-poor region Ref: Raymond Chang Chemistry, Ninth Edition Page 128 4.10

  12. A Brønsted acid must contain at least one ionizable proton! A Brønsted acid is a proton donor A Brønsted base is a proton acceptor base acid acid base Ref: Raymond Chang Chemistry, Ninth Edition Figure 4.8, Page 129 4.11

  13. HCl H+ + Cl- HNO3 H+ + NO3- CH3COOH H+ + CH3COO- H2SO4 H+ + HSO4- HSO4- H+ + SO42- HPO42- H+ + PO43- H2PO4- H+ + HPO42- H3PO4 H+ + H2PO4- Monoprotic acids Strong electrolyte, strong acid Strong electrolyte, strong acid Weak electrolyte, weak acid Diprotic acids Strong electrolyte, strong acid Weak electrolyte, weak acid Triprotic acids Weak electrolyte, weak acid Weak electrolyte, weak acid Weak electrolyte, weak acid 4.12

  14. HI (aq) H+ (aq) + Br- (aq) CH3COO- (aq) + H+ (aq) CH3COOH (aq) H2PO4- (aq) H+ (aq) + HPO42- (aq) H2PO4- (aq) + H+ (aq) H3PO4 (aq) Practice question: Identify each of the following species as a Brønsted acid, base, or both. (a) HI, (b) CH3COO-, (c) H2PO4- Brønsted acid Brønsted base Brønsted acid Brønsted base 4.13

  15. acid + base salt + water HCl (aq) + NaOH (aq) NaCl (aq) + H2O H+ + Cl- + Na+ + OH- Na+ + Cl- + H2O H+ + OH- H2O Neutralization Reaction 4.14

  16. 2Mg (s) + O2 (g) 2MgO (s) 2Mg 2Mg2+ + 4e- O2 + 4e- 2O2- 2Mg + O2 2MgO 4.4 Oxidation-Reduction Reactions REDOX REACTIONS(electron transfer reactions) Oxidation half-reaction (loss of e-) Reduction half-reaction (gain e-) OIL RIG Oxidation Is Loss Reduction Is Gain Oxidized Reducing Agent (donates electrons to oxygen and causes oxygen to be reduced) Reduced Oxidizing Agent (accepts electrons from Magnesium and causes Magnesium to be oxidized) 4.15

  17. Cu (s) + 2AgNO3 (aq) Cu(NO3)2 (aq) + 2Ag (s) Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s) Cu2+ + 2e- Cu Copper wire reacts with silver nitrate to form silver metal. What is the oxidizing agent in the reaction? Cu Cu2+ + 2e- Zn Zn2+ + 2e- Ag+ + 1e- Ag Zn is the reducing agent Zn is oxidized Cu2+is reduced Cu2+ is the oxidizing agent Ag+is reduced Ag+ is the oxidizing agent 4.16

  18. Oxidation numbers of all the elements in the following ? IF7 F = -1 7x(-1) + ? = 0 I = +7 K2Cr2O7 NaIO3 O = -2 K = +1 O = -2 Na = +1 3x(-2) + 1 + ? = 0 7x(-2) + 2x(+1) + 2x(?) = 0 I = +5 Cr = +6 4.17

  19. Types of Redox Reactions • Combination Reaction • Two or more substances combine to form a single product. • 0 0 +4 -2 • S(s) + O2 (g) SO2(g) (ii) Decomposition Reaction Breakdown of a compound into two or more components. +2 -2 0 0 2 HgO(s) 2Hg(l) + O2(g) 4.18

  20. (iii) Displacement Reaction Halogen displacement According to Activity Series F2 > Cl2 > Br2 > I2 i.e Molecular fluorine can replace chloride, bromide and iodide ions in solution. On the other hand, Molecular chlorine can replace bromide and iodide ions in solution 0 -1 -1 0 Cl2 (g) + 2 KBr(aq) 2KCl(aq) + Br2(l) 0 -1 -1 0 Cl2 (g) + 2 NaI(aq) 2NaCl(aq) + I2(l) 4.19

  21. Ca2+ + CO32- CaCO3 NH3 + H+ NH4+ Classify the following reactions. Zn + 2HCl ZnCl2 + H2 Ca + F2 CaF2 Precipitation Acid-Base Redox (H2 Displacement) Redox (Combination) 4.20

  22. moles of solute M = molarity = liters of solution 4.5 Concentration of Solutions concentration : amount of solute present in a given quantity of solvent or solution. Most commonly used unit is “Molarity” 4.21

  23. Moles of solute before dilution (i) Moles of solute after dilution (f) = Dilution Add Solvent = MfVf MiVi Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution. 4.22

  24. How would you prepare 60.0 mL of 0.2 M HNO3 from a stock solution of 4.00 M HNO3? MfVf 0.200 x 0.06 Vi = = 4.00 Mi MiVi = MfVf Mi = 4.00 Vi = ? L Mf = 0.200 Vf = 0.06 L = 0.003 L = 3 mL 3 mL of acid + 57 mL of water = 60 mL of solution 4.23

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