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29 September 2011

29 September 2011

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29 September 2011

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  1. 29 September 2011 • Objective: You will be able to: • predict the products of and write net ionic equations for precipitation reactions • work on the chapter 3 problem set

  2. Agenda • Precipitation Reactions • Predicting products • Writing ionic equations and net ionic equations • Practice Problems • Chapter 3 Problem Set Work Time Homework: Test Tuesday Chapter 3 problem set: Tuesday Chapter 4 Notes: Thursday

  3. You will be able to write and balance molecular, ionic and net ionic equations and predict the solubility of products.

  4. Reactions in Aqueous Solutions

  5. Introduction • Most chemical reactions and virtually all biological processes take place in water! • Three categories of reactions in aqueous solutions: • Precipitation reactions • Acid-Base reactions • Redox reactions

  6. Strong vs. Weak Electrolytes • Strong: Solute is 100% dissociated in water • http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf • Why is water good at hydrating ions?

  7. Acids and bases are electrolytes: • Some are strong: • Some are weak and ionize incompletely: • Double arrow indicates a reversible reaction: reaction can occur in both directions

  8. Reversible Reaction • Molecules ionize and then recombine • Until ionization is occurring as fast as recombination: chemical equilibrium

  9. Precipitation Reactions • formation of an insoluble product (precipitate) which separates from the solution. • This is also an example of a double displacement reaction

  10. Solubility • How do you predict whether a precipitate will form? • Depends on the solubility of the solute • p. 125-126 • Examples: • FeCO3 • KCl • AgCl

  11. Practice Determining Solubility • Ag2SO4 • CaCO3 • Na3PO4 • CuS • Ca(OH)2 • Zn(NO3)2

  12. Writing Equations • We don’t always write the entire chemical equation as if each species existed as a complete molecule • This doesn’t really reflect what’s actually happening!

  13. Molecular Equations • Written as though all species existed as molecules or whole units. • Doesn’t always reflect reality. • What’s actually happening? • Dissolved ionic compounds dissociate into ions!!

  14. Ionic Equation • Shows dissolved species as free ions. • Notice that there are ions that show up on both sides of the equation. • Spectator ions • They can be eliminated.

  15. Net Ionic Equation • To give this net ionic equation showing species that actually take place in the reaction:

  16. Example 1 • Solutions of barium chloride and sodium sulfate react to produce a white solid of barium sulfate and a solution of sodium chloride.

  17. Example 2 • A potassium phosphate solution is mixed with a calcium nitrate solution. Write a net ionic equation.

  18. Example 3 • Solutions of aluminum nitrate and sodium hydroxide are mixed. Write the net ionic equation for the reaction.

  19. Homework • Test Tuesday • Chapter 3 problem set: Tuesday • Chapter 4 Notes: Friday

  20. 5 October 2011 • Objective: You will be able to: • determine the identity of an unknown alkaline earth metal carbonate, M2CO3, using gravimetric analysis. • In your lab notebook: • Write a balanced molecular equation for the reaction between solutions of a group 2 metal (M2+) carbonate and calcium chloride.

  21. Agenda • Do now • Copper (II) sulfate hydrate lab… • Determining the formula of a metal carbonate by gravimetric analysis pre-lab Homework: Be sure your procedure is in your notebook, ready for lab tomorrow!

  22. Determining the formula of M2CO3 • Put the green cards in order. • Place the blue cards under each step for which you need those materials. • Have me check it when you think you’ve completed the procedure in the correct order. • Copy the steps, including detail about use of the materials to accomplish each step, into your lab notebook.

  23. 3 October 2011 • Objective: You will be able to: • write net ionic equations that predict the products of and describe acid-base reactions • Do now: • Find the mass of your precipitate + filter paper(s), record, and put it in the drying oven.

  24. Agenda • Do now • Acid-Base Reactions Notes and Problems • Find mass of precipitate again Homework: p. 160 #2, 3, 7, 9, 12, 17, 19, 22, 24a, 30, 31, 33: due tomorrow

  25. Acid-Base Reactions

  26. Properties of Acids and Bases • Arrhenius definition: • Acids: ionize in water to produce H+ ions • Bases: ionize in water to produce OH- ions

  27. Acids • React with metals like Zn, Mg, Fe to produce hydrogen gas 2HCl(aq) + Mg(s)  MgCl2(aq) + H2(g) • React with carbonates and bicarbonates to produce CO2(g) 2HCl(aq) + CaCO3(s) CaCl2(aq) + H2O(l) + CO2(g) HCl(aq) + NaHCO3(s)  NaCl(aq) + H2O(l) + CO2(g)

  28. Brønsted Definition • Acid: proton donor • Base: proton acceptor • don’t need to be aqueous! • HCl(aq)  H+(aq) + Cl-(aq) proton

  29. But… • HCl(aq)  H+(aq) + Cl-(aq) • H+ is very attracted to the negative pole (O atom) in H2O • HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq) • H3O+ : hydronium ion • Above, a Brønstedacid (HCl) donates a proton to a Brønstedbase (H2O)

  30. Types of Acids • Monoprotic: each one yields one hydrogen ion upon ionization • Ex: HCl, HNO3, CH3COOH, • Diprotic: each gives two H+ ions • Ex: H2SO4 • H2SO4(aq)  H+(aq) + HSO4-(aq) • HSO4-(aq) > H+(aq) + SO42-(aq) • Triprotic: 3 H+

  31. Strong vs. Weak Acids Strong Acids Dissociate completely Weak Acids Dissociate Incompletely • HCl hydrochloric • HBrhydrobromic • HI hydroiodic • HNO3 nitric • H2SO4 sulfuric • HClO3chloric • HClO4perchloric • HF hydrofluoric • HNO2 nitrous • H3PO4 phosphoric • CH3COOH acetic

  32. Brønsted Bases • H+(aq) + OH-(aq)  H2O(l) • Here, the hydroxide ion accepts a proton to form water. • OH- is a Brønstedbase. • NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq)

  33. 13 October 2011 • Take Out Homework • Objective: You will be able to: • write net ionic equations that predict the products of and describe acid-base reactions • Homework Quiz: Week of 10/12 a. You have a solution of sodium chloride and want to precipitate out the chloride ions. What ionic compound can you add? b. Write the molecular and net ionic equations for this reaction.

  34. Agenda • Homework Quiz • Check Homework • Acid-Base Reactions Notes and Examples • Practice Problems Homework: p. 161 #30, 31, 33; worksheet 1-3: due Monday Lab calculations: Monday

  35. Brønsted Acid or Base? • HBr • NO2- • HCO3- • SO42- • HI

  36. Acid-Base Neutralization • reaction between an acid and a base • produce water and a salt • salt: ionic compound (not including H+ or OH- or O2-) • acid + base  water + salt • Strong acid + Strong base example • HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) • Write the ionic and net ionic equations! • Which are spectator ions?

  37. Weak acid + Strong base example: • HCN(aq) + NaOH(aq)  NaCN(aq) + H2O(l) • HCN does not ionize completely • HCN(aq) + Na+(aq) + OH-(aq)  Na+(aq) + CN-(aq) + H2O(l) • Write the net ionic equation

  38. Write equations • CH3COOH(aq) + KOH(aq) • H2CO3(aq) + NaOH(aq) • HNO3(aq) + Ba(OH)2(aq)

  39. 17 October 2011 • Take Out Lab Notebook • Objective: You will be able to: • Predict the products of and write net ionic equations for acid-base reactions producing gases. • Homework Quiz: (Week of Oct. 17) • Write the net ionic equation for the reaction of solutions of carbonic acid and sodium hydroxide.

  40. Agenda • Homework Quiz • Acid-Base reactions that produce gases Examples and problems • Practice Problems • Redox reactions Homework: Quiz tomorrow (one precip, one strong acid-strong base, one weak acid-strong base, one acid-salt producing gas)

  41. Acid-Base Reaction: Gas Formation • Some salts (with CO32-, SO32-, S2-, HCO3-) react with acids to form gaseous products Na2CO3(aq) + 2HCl(aq)  2NaCl(aq) + H2CO3(aq) Then the carbonic acid breaks down: H2CO3(aq)  H2O(l) + CO2(g)

  42. Practice Problems • NaHCO3(aq) + HCl(aq) • Na2SO3(aq) + HCl(aq) • K2S (aq) + HCl(aq)

  43. Practice Problems Worksheet

  44. 18 October 2010 • Objective: You will be able to: • model the transfer of electrons between reactants in redox reactions by correctly writing oxidation and reduction half reactions and overall reactions; determine oxidation numbers. • Do now: Review the strong acids and gases formed by the reaction of salts with acids (5 min.)

  45. Agenda • Do now • Writing equations quiz • Redox equations – differentiating between oxidation and reduction half reactions. Homework: Review p. 135-145: tomorrow

  46. Quiz – 25 min.

  47. Oxidation-Reduction Reactions • What was being transferred in acid-base reactions? • Protons! • Redox reactions: electron transfer!

  48. 2Mg(s) + O2(g)  2MgO(s) • Mg2+ bonds with O2- • What’s happening with electrons? • Two steps, 2 half reactions: 2Mg  2Mg2+ + 4e- O2 + 4e-  2O2- 2Mg + O2 + 4e-  2Mg2+ + 202- + 4e- 2Mg + O2  2Mg2+ + 2O2- 2Mg2+ + 2O2-  2MgO

  49. Oxidation: Half reaction that refers to the LOSS of electrons • Reduction: Half reaction that refers to the GAIN of electrons 2Mg  2Mg2+ + 4e- O2 + 4e-  2O2- • Reducing agent: donates electrons • Oxidizing agent: accepts electrons