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Chemists Have Solutions I

Chemists Have Solutions I. Solution Chemistry. Chemists Have Solutions. Solution Concentrations (Molarity, Molality, Percent) Acids and Bases Theories Arrhenius, Brønsted-Lowry, Lewis Strong and Weak Acids and Bases The pH scale Neutralization Reactions: Concepts and Problems

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Chemists Have Solutions I

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  1. Chemists Have Solutions I Solution Chemistry

  2. Chemists Have Solutions • Solution Concentrations (Molarity, Molality, Percent) • Acids and Bases • Theories • Arrhenius, Brønsted-Lowry, Lewis • Strong and Weak Acids and Bases • The pH scale • Neutralization Reactions: Concepts and Problems • Applications in Industry, Household, Health • Basic Reduction and Oxidation • Definitions: Oxidation, Reduction, Reducing Agent, Oxidizing Agent • Redox Reactions • Applications and Examples: Batteries, Corrosion, Common oxidizing and reducing agents

  3. Solution Solvent Solute A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent is the substance present in the larger amount Soft drink (l) Air (g) Pb Sn Soft Solder (s) 4.1

  4. nonelectrolyte weak electrolyte strong electrolyte An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity. A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity. 4.1

  5. H2O NaCl (s)Na+ (aq) + Cl- (aq) CH3COOHCH3COO- (aq) + H+ (aq) Conduct electricity in solution? Cations (+) and Anions (-) Strong Electrolyte – 100% dissociation Weak Electrolyte – not completely dissociated 4.1

  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. 4.1

  7. d- d+ H2O Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner. 4.1

  8. H2O C6H12O6 (s) C6H12O6 (aq) Nonelectrolyte does not conduct electricity? No cations (+) and anions (-) in solution 4.1

  9. precipitate Pb(NO3)2(aq) + 2KI (aq) PbI2(s) + 2KNO3(aq) Recall: Precipitation Reactions Precipitate – insoluble solid that separates from solution molecular equation 4.2

  10. Water + carbon dioxide carbonic acid (dissolves CaCO3) Calcium bicarbonate to calcium carbonate, water, CO3 Chemistry In Action: Stalactite Formation 4.2

  11. moles of solute M = molarity = What mass of KI is required to make 500. mL of a 2.80 M KI solution? liters of solution volume KI moles KI grams KI Solution Stoichiometry The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. 4.5

  12. Solution Composition Molarity (M) Molarity: Moles of solute per liter of solution.

  13. Test Yourself • How many moles of potassium bromide are in 200.0mL of a 1.5M solution? • What is the concentration, in M, of 20.00g Lead (II) Nitrate in 50.0L of solution? • What is the concentration, in M, of 30.0g glucose (C6H12O6), in 100.0 mL of water? Assume no volume changes. • How much salt must I dissolve in 2.00L water to make a 5.0M solution? Assume no volume changes. • What will be the mass of table salt I can recover from the complete drying of 50.00mL 0.50M salt solution?

  14. Solution Composition MOLALITY (m) Molality: Moles of solute per kilogram solvent.

  15. Percent Concentration (pph) • Also pph: part per hundred • % Conc. (v/v) = vol. solute x 100% vol. sol’n. • % Conc. (w/v) = mass. Solute (g) x 100% vol. sol’n. (mL) What is the % concentration of 20.0mL pure ethanol diluted to 100.0mL? What is the molarity of 50% (w/v) NaOH?

  16. 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. 4.5

  17. How would you prepare 60.0 mL of 0.2 M HNO3 from a stock solution of 4.00 M HNO3? MiVi = MfVf 4.5

  18. Test Yourself • I have 20.0L of 1.00M HCl. If I need 0.500M HCl, to what final volume must I add water to the HCl I have? • I need to make 200.0mL of 0.350M NaOH. I have an unlimited supply of water and stock 0.50M NaOH. What must I do?

  19. Test Yourself: Solution Stoichiometry • Lead (II) nitrate and potassium iodide react in a methathesis reaction to form insoluble lead (II) iodide and aqueous potassium nitrate. If I combine 10.0mL of 0.1000M lead (II) nitrate with 5.00mL of 0.2000M potassium iodide, what will be the mass of lead iodide produced? • I produced 1.00g of lead (II) iodide in the reaction above by combining 10.0mL of lead (II) nitrate with an excess of potassium iodide. What was the concentration of lead (II) nitrate solution?

  20. Chemists Have Solutions II Acids and Bases

  21. 2HCl (aq) + Mg (s) MgCl2 (aq) + H2 (g) 2HCl (aq) + CaCO3 (s) CaCl2 (aq) + CO2 (g) + H2O (l) Acids Have a sour taste. Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid. Cause color changes in plant dyes. React with certain metals to produce hydrogen gas. React with carbonates and bicarbonates to produce carbon dioxide gas Aqueous acid solutions conduct electricity. 4.3

  22. Bases Have a bitter taste. Feel slippery. Many soaps contain bases. Cause color changes in plant dyes. Aqueous base solutions conduct electricity. 4.3

  23. Arrhenius acid is a substance that produces H+ (H3O+) in water Arrhenius base is a substance that produces OH- in water 4.3

  24. 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 4.3

  25. 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 4.3

  26. HI (aq) H+ (aq) + Br- (aq) CH3COO- (aq) + H+ (aq) CH3COOH (aq) H2PO4- (aq) H+ (aq) + HPO42- (aq) H2PO4- (aq) + H+ (aq) H3PO4 (aq) 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 4.3

  27. + H H O O [ ] + + - H H H O H O H H H2O (l) H+(aq) + OH-(aq) H2O + H2O H3O+ + OH- Acid-Base Properties of Water autoionization of water conjugateacid base conjugatebase acid 15.2

  28. Hydronium ion, hydrated proton, H3O+ 4.3

  29. [H+][OH-] Kc = [H2O] H2O (l) H+(aq) + OH-(aq) The Ion Product of Water [H2O] = constant Kc[H2O] = Kw = [H+][OH-] The ion-product constant (Kw) is the product of the molar concentrations of H+ and OH- ions at a particular temperature. Solution Is [H+] = [OH-] neutral At 250C Kw = [H+][OH-] = 1.0 x 10-14 [H+] > [OH-] acidic [H+] < [OH-] basic 15.2

  30. = [OH-] = 1 x 10-14 Kw 1.3 [H+] What is the concentration of OH- ions in a HCl solution whose hydrogen ion concentration is 1.3 M? Kw = [H+][OH-] = 1.0 x 10-14 [H+] = 1.3 M = 7.7 x 10-15M 15.2

  31. pH [H+] pH – A Measure of Acidity pH = -log [H+] Solution Is At 250C neutral [H+] = [OH-] [H+] = 1 x 10-7 pH = 7 [H+] > 1 x 10-7 pH < 7 acidic [H+] > [OH-] basic [H+] < [OH-] [H+] < 1 x 10-7 pH > 7 15.3

  32. pOH = -log [OH-] [H+][OH-] = Kw = 1.0 x 10-14 -log [H+] – log [OH-] = 14.00 pH + pOH = 14.00 15.3

  33. The pH Scale

  34. The pH Scale Measuring pH

  35. The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood? The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H+ ion concentration of the rainwater? pH = -log [H+] = 10-4.82 = 1.5 x 10-5M [H+] = 10-pH NOTE that pH 4.82 only has TWO significant figures. Thus, our final answer also has TWO significant figures pH + pOH = 14.00 pOH = -log [OH-] = -log (2.5 x 10-7) = 6.60 pH = 14.00 – pOH = 14.00 – 6.60 = 7.40 NOTE that 2.5 x 10-7M has TWO significant figures. The answers in pH and pOH, therefore, must also have two sig.figs. BUT, we only start counting sig.figs AFTER the decimal point for pH and pOH (as well as other “p” values). 15.3

  36. H2O NaCl (s)Na+ (aq) + Cl- (aq) HCl (aq) + H2O (l) H3O+(aq) + Cl-(aq) HNO3(aq) + H2O (l) H3O+(aq) + NO3-(aq) CH3COOHCH3COO- (aq) + H+ (aq) HClO4(aq) + H2O (l) H3O+(aq) + ClO4-(aq) H2SO4(aq) + H2O (l) H3O+(aq) + HSO4-(aq) Strong Electrolyte – 100% dissociation Weak Electrolyte – not completely dissociated Strong Acids are strong electrolytes 15.4

  37. HF (aq) + H2O (l) H3O+(aq) + F-(aq) HNO2(aq) + H2O (l) H3O+(aq) + NO2-(aq) HSO4-(aq) + H2O (l) H3O+(aq) + SO42-(aq) H2O (l) + H2O (l) H3O+(aq) + OH-(aq) H2O NaOH (s) Na+(aq) + OH-(aq) H2O KOH (s) K+(aq) + OH-(aq) H2O Ba(OH)2(s) Ba2+(aq) + 2OH-(aq) Weak Acids are weak electrolytes Strong Bases are strong electrolytes 15.4

  38. F-(aq) + H2O (l) OH-(aq) + HF (aq) NO2-(aq) + H2O (l) OH-(aq) + HNO2(aq) Weak Bases are weak electrolytes • Conjugate acid-base pairs: • The conjugate base of a strong acid has no measurable strength. • H3O+ is the strongest acid that can exist in aqueous solution. • The OH- ion is the strongest base that can exist in aqeous solution. 15.4

  39. 15.4

  40. Strong Acid Weak Acid 15.4

  41. What is the pH of a 1.8 x 10-2 M Ba(OH)2 solution? HNO3(aq) + H2O (l) H3O+(aq) + NO3-(aq) Ba(OH)2(s) Ba2+(aq) + 2OH-(aq) What is the pH of a 2 x 10-3 M HNO3 solution? HNO3 is a strong acid – 100% dissociation. 0.0 M 0.0 M Start 0.002 M 0.0 M 0.002 M 0.002 M End pH = -log [H+] = -log [H3O+] = -log(0.002) = 2.7 Ba(OH)2 is a strong base – 100% dissociation. 0.0 M 0.0 M Start 0.018 M 0.0 M 0.018 M 0.036 M End pH = 14.00 – pOH = 14.00 + log(0.036) = 12.56 15.4

  42. Definition of An Acid + OH- H H + H O H + H+ H N H N H • • • • • • • • • • • • H H Arrhenius acid is a substance that produces H+ (H3O+) in water A Brønsted acid is a proton donor A Lewis acid is a substance that can accept a pair of electrons A Lewis base is a substance that can donate a pair of electrons H+ acid base acid base 15.12

  43. H F F F B F B N H F F H H N H H • • Lewis Acids and Bases + acid base No protons donated or accepted! 15.12

  44. NaHCO3 (aq) + HCl (aq) NaCl (aq) + H2O (l) + CO2 (g) Mg(OH)2 (s) + 2HCl (aq) MgCl2 (aq) + 2H2O (l) Chemistry In Action: Antacids and the Stomach pH Balance

  45. acid + base salt + water HCl (aq) + NaOH (aq) NaCl (aq) + H2O H+ + Cl- + Na+ + OH- Na+ + Cl- + H2O H+ + OH- H2O Neutralization Reaction 4.3

  46. Sample Problem • Sodium hydroxide reacts with HCl in a neutralization reaction. If I mix 30mL of 0.2000M NaOH and 50mL of 0.1000M HCl, how many moles of NaCl will be produced? Follow-up question: What will be the final concentration of this salt? (Take note of the final volume of the combined solution.)

  47. Test yourself • What will be the pH of a 0.000211M HCl solution? • I dissolved 1.00g of NaOH in 1.000L solution. What will be the final pH? • What volume of 0.2000M NaOH is needed to completely neutralize 20.00mL of 0.1000M HCl? If I evaporate the end product, what mass of salt will I obtain? • I combined 10.00mL 0.2000M NaOH with 30.00mL 0.2000M HCl. What will be the final pH of the final solution created? (TIP: The final pH will be based on any unreacted H+ or OH-. Assume all volumes are simply additive.)

  48. Chemists Have Solutions III Redox Reactions

  49. 2Mg (s) + O2 (g) 2MgO (s) 2Mg 2Mg2+ + 4e- O2 + 4e- 2O2- 2Mg + O2 + 4e- 2Mg2+ + 2O2- + 4e- 2Mg + O2 2MgO Oxidation-Reduction Reactions (electron transfer reactions) Oxidation half-reaction (lose e-) Reduction half-reaction (gain e-) Magnesium lost electrons. Thus, Mg is is oxidized. It is the reducing agent. O2gained electrons. Thus, O2 is reduced. It is the oxidizing agent. 4.4

  50. Some Mnemonics • OIL RIG • Oxidation Is Loss of electrons, Reduction Is Gain of electrons • LEO GER • Loss of Electrons is Oxidation. Gain of Electrons is Reduction • What is Oxidized is the reducing agent • What is Reduced is the oxidizing agent

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