Reactions in Aqueous Solution Chapter 4 (semester 2/2011) 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

General Properties of Aqueous Solutions Solution = [ solute + solvent] [smaller amount +larger amount] [CLEAR, HOMOGENEOUS MIXTURE] Aqueous solution = solute (liquid “ or ” solid) + solvent (water) SolutionSolventSolute Sea water Air (g) Alloy H2OH2O N2N2 Cu Salt (NaCl) O 2, Ar, CH 4 Ni

Two types of Solutes nonelectrolyte weak electrolyte strong electrolyte 4.2 Non-electrolyte When dissolved in water does not conduct electricity Electrolyte When dissolved in water can conduct electricity Incomplete dissociation/reversible 100%dissociation/ One sided reaction Ref: Raymond Chang Chemistry, Tenth Edition Figure 4.1, Page 122

Strong Electrolyte – 100% dissociation NaCl (s) Na + (aq) + Cl - (aq) H2OH2O Weak Electrolyte – not completely dissociated CH 3 COOH CH 3 COO - (aq) + H + (aq) Conduct electricity in solution? Dissociation means breaking up into..Cations (+) and Anions (-) 4.3 Note: Pure water contains very few ions, cannot conduct electricity (extremely weak electrolyte)

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

Ionization of acetic acid CH 3 COOH CH 3 COO - (aq) + H + (aq) 4.5 A reversible reaction. The reaction can occur in both directions. Acetic acid is a weak electrolyte because its ionization in water is incomplete.

Nonelectrolyte does not conduct electricity? No cations (+) and anions (-) in solution 4.6 C 6 H 12 O 6 (s) C 6 H 12 O 6 (aq) H2OH2O

4.2 Precipitation Reactions (Metathesis reaction) or (Double Displacement reaction) One product is insoluble solid molecular equation ionic equation net ionic equation Pb NO Na + + 2I - PbI 2 (s) + 2Na + + 2NO 3 - Na + and NO 3 - are spectator ions Pb(NO 3 ) 2 (aq) + 2NaI (aq) PbI 2 (s) + 2NaNO 3 (aq) precipitate Pb I - PbI 2 (s) 4.7

4.8 Solubility: Maximum amount of solute that will dissolve in a given quantity of solvent in a specific temperature. Substances: soluble 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: (NH 4 ) 2 CO 3, (NH 4 ) 3 PO 4,(NH 4 ) 2 S,(NH 4 ) 2 CrO 4

ACID: Arrhenius acid is a substance that produces H + (H 3 O + ) in water BASE: Arrhenius base is a substance that produces OH - in water Acid-Base Reactions

Hydronium ion, hydrated proton, H 3 O

A Brønsted acid is a proton donor A Brønsted base is a proton acceptor acidbaseacidbase 4.11 A Brønsted acid must contain at least one ionizable proton!

Monoprotic acids HCl H + + Cl - HNO 3 H + + NO 3 - CH 3 COOH H + + CH 3 COO - Strong electrolyte, strong acid Weak electrolyte, weak acid Diprotic acids H 2 SO 4 H + + HSO 4 - HSO 4 - H + + SO 4 2- Strong electrolyte, strong acid Weak electrolyte, weak acid Triprotic acids H 3 PO 4 H + + H 2 PO 4 - H 2 PO 4 - H + + HPO 4 2- HPO 4 2- H + + PO 4 3- Weak electrolyte, weak acid 4.12

Practice question: Identify each of the following species as a Brønsted acid, base, or both. (a) HI, (b) CH 3 COO -, (c) H 2 PO 4 - HI (aq) H + (aq) + Br - (aq)Brønsted acid CH 3 COO - (aq) + H + (aq) CH 3 COOH (aq)Brønsted base H 2 PO 4 - (aq) H + (aq) + HPO 4 2- (aq) H 2 PO 4 - (aq) + H + (aq) H 3 PO 4 (aq) Brønsted acid Brønsted base 4.13

Neutralization Reaction acid + base salt + water HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O H + + Cl - + Na + + OH - Na + + Cl - + H 2 O H + + OH - H 2 O 4.14

4.4 Oxidation-Reduction Reactions REDOX REACTIONS(electron transfer reactions) 2Mg (s) + O 2 (g) 2MgO (s) 2Mg 2Mg e - O 2 + 4e - 2O 2- Oxidation half-reaction (loss of e - ) Reduction half-reaction (gain e - ) 2Mg + O 2 2MgO 4.15 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) OILRIG Oxidation Is Loss Reduction Is Gain

Zn (s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu (s) Zn is oxidizedZn Zn e - Cu 2+ is reducedCu e - Cu Zn is the reducing agent Cu 2+ is the oxidizing agent 4.16 Copper wire reacts with silver nitrate to form silver metal. What is the oxidizing agent in the reaction? Cu (s) + 2AgNO 3 (aq) Cu(NO 3 ) 2 (aq) + 2Ag (s) Cu Cu e - Ag + + 1e - AgAg + is reducedAg + is the oxidizing agent

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

Types of Redox Reactions (i)Combination Reaction Two or more substances combine to form a single product S (s) + O 2 (g) SO 2(g) (ii) Decomposition Reaction Breakdown of a compound into two or more components HgO (s) 2Hg (l) + O 2(g) 4.18

(iii) Displacement Reaction Halogen displacement According to Activity Series F 2 > Cl 2 > Br 2 > I 2 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 Cl 2 (g) + 2 KBr (aq) 2KCl (aq) + Br 2(l) Cl 2 (g) + 2 NaI (aq) 2NaCl (aq) + I 2(l) 4.19

Ca 2+ + CO 3 2- CaCO 3 NH 3 + H + NH 4 + Zn + 2HCl ZnCl 2 + H 2 Ca + F 2 CaF 2 Precipitation Acid-Base Redox (H 2 Displacement) Redox (Combination) Classify the following reactions. 4.20

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

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

How would you prepare 60.0 mL of 0.2 M HNO 3 from a stock solution of 4.00 M HNO 3 ? M i V i = M f V f M i = 4.00 M f = 0.200V f = 0.06 L V i = ? L 4.23 V i = MfVfMfVf MiMi = x = L = 3 mL 3 mL of acid + 57 mL of water= 60 mL of solution Ref: power point presentation for instructors (Mc- Graw hill series,

25 Chemistry in Action: Breath Analyzer 3CH 3 COOH + 2Cr 2 (SO 4 ) 3 + 2K 2 SO H 2 O 3CH 3 CH 2 OH + 2K 2 Cr 2 O 7 + 8H 2 SO

26 Preparing a Solution of Known Concentration