1. Chapter 4: RXN TYPES and SOLN STOICHIOMETRY (2) Aqueous Solutions and Electrolytes Precipitation, Acid-Base, Oxidation-Reduction (Redox) Reactions

2. CHEMICAL RXNS IN AQUEOUS SOLNS (4.4) Precipitation is the formation of solid from two aqueous solutions. Acid-Base neutralization is the formation of water. Oxidation-Reduction or redox is the transfer of electrons from one reactant atom to another reactant atom.

3. PRECIPITATION (4.5, 4.7) The formation of a solid (precipitate) when two aqueous solutions are mixed; we say that the product cmp is insoluble or only slightly soluble in water. Soluble salt I (aq) + Soluble salt II (aq)  Solid cmp (s) + Soluble salt III Table 4.1 Solubility Rules for Salts in Water (memorize) Ion interchange or metathesis (switch cation/anion partners)

4. T4.1 SOLUBILITY RULES Practice Prob 35, 37, 4, 43 1.Most nitrates are soluble 2.Most salts with Grp 1A ions and NH 4 + are soluble. 3.Most salts with Cl -, Br -, I - are soluble EXCEPT those with Ag +, Pb 2+, Hg 2 2+ 4.Most sulfates are soluble EXCEPT those with Ba 2+, Pb 2+, Hg 2 2+, Ca 2+. 5.Most hydroxides are slightly soluble EXCEPT the strong bases (Ca, Sr, Ba). 6.Most sulfides, carbonates, chromates and phosphates are slightly soluble.

5. Fig 4.13 K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq)  KNO 3 (aq) + BaCrO 4 (s)

6. CHEMICAL EQUATION (4.6) Identify reactants, products, states of matter [g, s, aq, ℓ]. Balance equation to conserve mass (and charge). Calculate quantitative or stoichiometric relationships (mol ratios) between rxn participants (R or P) based on balanced chemical rxn.

7. CHEMICAL EQUATIONS (2) Formula Equation: write all reactants and products as “neutral molecules”, show state of each. Complete Ionic Equation: write strong electrolytes as ions (aq). Net Ionic Equation: cancel out spectator ions. This eqn expresses the basic chemical rxn.

8. Figure 4.15 a&b The Reaction of K 2 CrO 4 and Ba(NO 3 ) 2

9. Chapter 4 Problems 36, 38, 44, 46

10. SOLUTION STOIOCHIOMETRY (Ch 4 + Ch 3 + Ch 2) Typical stoichiometric calculation for reactions taking place in aq soln. 1.Write balanced net ionic eqn to identify the chem reaction 2.Calculate mols of known A from V A and M A 3.Calculate mols of unknown B, then V B 4. V A, M A  #mol A  #mol B  V B if M A and M B are known 5.Determine LR after Step 1 if appropriate.

11. STOICHIOMETRIC PROBLEMS 48, 50

12. ACID + BASE RXNS Acids donate protons, i.e. provide H + (aq) or H 3 O + (aq, hydronium) ions in water (Arrhenius). Polyprotic acids: sulfuric, phosphoric. Bases accept protons. Review Ch 2 nomenclature and Ch 4 strong acids (SA) and bases (SB).

13. ACID + BASE RXN: NEUTRALIZATION Acid + Base → Salt + Water SA + SB: HCl (aq) + NaOH(aq) → NaCl(aq) + H 2 O(ℓ) –Net ionic:H + (aq) + OH - (aq) → H 2 O(ℓ) WA + SB: HF(aq) + KOH(aq) → KF(aq) + H 2 O(l) –Net ionic: HF(aq) + OH - (aq) → F - (aq) + H 2 O(ℓ) SA + WB: Problem 4.57c

14. ACID + BASE NEUTRALIZATION The key in a neutralization reaction is that one H + ion reacts with one OH - ion. It is NOT that one mol acid reacts with one mol base. –Be careful with acids that provide 2 or 3 H + ions per mol acid (sulfuric or phosphoric). –Similarly for bases like barium hydroxide.

15. ACID-BASE TITRATION (volumetric analysis) Exptal technique for determining quantity of an unknown substance (analyte in beaker) by reacting a measured volume of it with another reactant (titrant in buret) of known concentration. This method works when the rxn is 100% complete (reaches equivalence pt) and that there is an indicator (color change, pH) that signals the rxn completion (endpoint).

16. NEUTRALIZATION TITRATION Write the balanced acid (assume to be analyte) + base (use strong base) rxn for the titration. Use an indicator (e.g. phenolphthalein) that signals the equivalence point. The molarity and volume of the titrant (SB) must be known accurately. Fig 4.18

17. NEUTRALIZATION TITRATION Prob 4.64 and 4.66 (This is what you will do in lab)

18. OXIDATION-REDUCTION REACTIONS A redox reaction involves the transfer of electrons between atoms in the reactants. Electrons gained by one atom must equal electrons lost by another. (conservation of e-s) Oxidation states or numbers are assigned to atoms and they change in a redox rxn. Both oxidation and reduction must occur simultaneously. (or e-s would not be conserved) 2

19. OXIDATION STATES OR NUMBERS (OX#) Actual or imaginary charge on atom: single atom, atom in molecule or atom in polyatomic ion We use these OX#s to keep track of electrons in redox rxns. We will study rules for assigning OX# and then use this information to balance redox equations

20. DETERMINING OX# (T4.2) OX# of an atom in an element is 0 [Fe, O 2 ] If the species is neutral, sum of OX# is 0 [NaCl, MnO 2 ] If the species is charged, sum of OX# is value of overall charge (NH 4 + ; SO 4 2- ) OX# of a monatomic ions is its charge: 1A atoms have OX# = +1; 2A atoms have OX# = +2; 7A atoms have OX# = -1, etc

21. OX# (2) In molecular (covalent) cmps O has OX# = -2; sometimes -1 (with metal) In molecular (covalent) cmps H has OX# = +1; sometimes -1 (peroxide) F always has OX# = -1; other halides can have other OX#s There are exceptions

22. OXIDATION If atom X in compound A loses electrons and becomes more positive (OX# increases), we say X (with charge) or A is oxidized. Also, we say that A is the reducing agent (RA) or is the electron donor.

23. REDUCTION If atom Y in compound B gains electrons and becomes more negative (OX# decreases), we say Y (with charge) or B is reduced. Also, we say that B is the oxidizing agent (OA) or is the electron acceptor.

24. Figure 4.20 A Summary of Oxidation- Reduction Process

25. Redox Basics Prob 68, 72

26. ACTIVITY SERIES (Expt 7) Redox participants have varying capacities to gain or lose electrons. The Activity Series lists metal elements in order of decreasing strength as a reducing agent; ie. ability to lose electrons and undergo oxidation. A particular rxn in the list will cause the reduction of any rxn below it.

27. Activity Series of Metals in Aqueous Solution

28. INTERPRETATION OF ACTIVITY SERIES What rxn will occur between lithium and calcium? The choices are –Li(s) + Ca(s)  Li + (aq) + Ca 2+ (aq) –2Li(s) + Ca 2+ (aq)  2Li + (aq) + Ca(s) –2Li + (aq) + Ca(s)  Ca 2+ (aq) + 2Li(s) –2Li + (aq) + Ca 2+ (aq)  2Li(s) + Ca(s) The strongest RA is at the top (Li) meaning that Li loses e-s and is oxidized. And Ca 2+ gains e-s and must be reduced.

29. INTERPRETATION OF ACTIVITY SERIES Therefore when Lithium and Calcium react, 2Li(s) + Ca 2+ (aq)  2Li + (aq) + Ca(s) We say that Li displaces calcium ion from soln. Li(s) dissolves and Ca(s) forms

30. BALANCING REDOX EQNS Half-Rxn Method (acid) Write half chem eqn for reduction –This requires determining what atom is reduced; use OX#s Write half chem eqn for oxidation –same Balance all atoms except H and O Balance O with H 2 O and H with H +

31. Half-Reaction Method (acid, 2) Add electrons to balance charge (I.e. show loss or gain of electrons) Balance the number of electrons between the two half-rxns by multipying by appropriate factor –#e- gained by atom Y = #e- lost by atom X) Add two half-rxns and cancel identical species. Check for atom and charge balance

32. The Half-Reaction Method (Acidic Solution)

33. Half-Reaction Method (base) Follow steps for balancing in acid Add OH - ions to cancel out the H + ions, thus forming water. Cancel out water molecules Check for atom and charge balance. Make sure there are no H + ions remaining.

34. Balancing Redox Equations Prob 74, 76