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Unit 4 Page 370-377

Acids & Bases. pOH. Unit 4 Page 370-377. pH. 1887: Defined acid: Produces H + in water (acidic solutions). Svante Arrhenius. H + ions released are bonded to the water molecule to form H 3 O + ions H + (aq) + H 2 O (l) H 3 O + (aq).

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Unit 4 Page 370-377

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  1. Acids & Bases pOH Unit 4 Page 370-377 pH

  2. 1887: Defined acid: Produces H+ in water (acidic solutions) Svante Arrhenius H+ ions released are bonded to the water molecule to form H3O+ ions H+ (aq) + H2O (l) H3O+ (aq) H2O + H2CO3 H3O+ + HCO3-

  3. Note: H+ (aq) + H2O (l) H3O+ (aq) Is a reversible reaction: the double arrows indicate that this reaction proceeds at equal rates in each direction. This reaction is in dynamic equilibrium; hydronium ions are created as fast as they are breaking down to produce hydrogen ions and water.

  4. 1887: Defined base: Produces OH- in water (alkaline solutions) Svante Arrhenius Bases are normally a cation (+) and a hydroxide ion. K+OH- (s) + H2O (l) K+ (aq) + OH- (aq) Ba(OH)2 + H2O (l) Ba+2 (aq) + 2 OH- (aq)

  5. 1887: Neutralization Reaction Svante Arrhenius When equal amounts of H+ ions react with OH- ions, water is the only product. H3O+ (aq) + OH- (aq) 2 H2 O (l)

  6. Johannes Brönsted 1923 Brönsted and Lowry independently published their findings, which is known as the Brönsted-Lowry theory or concept. • Hydrogen ions are protons • Acids are proton donors • Bases are proton acceptors • Acids increase [H+] • Bases decrease [H+] Thomas Lowry

  7. Johannes Brönsted “Acids and bases are substances that are capable of splitting off or taking up hydrogen ions, respectively.” Bases accept hydrogen ions. This is why NH3 is a base under the Brönsted-Lowry theory but not under the Arrhenius theory. NH3 + H2O NH4+ + OH- (Base) (Acid) (Acid) (Base)

  8. When an acid donates a proton, it is then able to accept a proton, so it becomes a conjugate base. When a base accepts a proton, it is then able to donate a proton and becomes a conjugate acid.

  9. Now try your hand at identifying the conjugate acid-base pairs in the equations shown below. congugatebase congugateacid acid base Proton donor Proton acceptor Proton acceptor Proton donor

  10. Exercise: Complete “Developing Skills” on page 372 (C.5 – Acids and Bases) to pass in.

  11. 1909 Developed pH Scale (potential hydrogen) Sören Sörensen Based on the solution’s MOLAR concentration of the H+ ions.

  12. Solution: homogeneous mixture of a solute dissolved in a solvent Acidic solution: hydronium ion concentration is greater than hydroxide concentration Basic (alkaline) solution: hydroxide ion concentration is greater than the hydronium ion concentration Neutral solution: hydronium ion concentration equals the hydroxide ion concentration

  13. Hydronium and hydroxide ion concentrations are measured in moles per liter, or molarity, and its symbol is M Ex: 2.0 moles of NaCl (116 g) dissolved in Water to make 1.0 liters of solution has a molarity of: 2.0 moles 1.0 L 2.0 M =

  14. Likewise: 0.16 moles of NaCl (116 g) dissolved in Water to make 2.0 liters of solution has a molarity of: 0.16 moles 2.0 L = 0.080 M Problem: Find molarity of 5 grams HCl dissolved in water to make 250 mL of solution. 5 g x 1mol = 0.14 mol 0.14 mol = 0.56 M 36 g 0.25 L Solution:

  15. pH Scale • We use this scale to measure the strength of an acid or base. • pH is defined as the –log[H+] • (negative log of the hydrogen ion concentration, in moles per liter) • pH can use the concentration of hydronium ions or hydrogen ions.

  16. pH Scale 7 Acid Base 0 14 Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 515

  17. Acidic pH Scale Neutral Basic or Alkaline

  18. pH of Common Substances Timberlake, Chemistry 7th Edition, page 335

  19. pH and pOH of Common Substances pH [H1+] [OH1-] pOH 14 1 x 10-14 1 x 10-0 0 13 1 x 10-13 1 x 10-1 1 12 1 x 10-12 1 x 10-2 2 11 1 x 10-11 1 x 10-3 3 10 1 x 10-10 1 x 10-4 4 9 1 x 10-9 1 x 10-5 5 8 1 x 10-8 1 x 10-6 6 6 1 x 10-6 1 x 10-8 8 5 1 x 10-5 1 x 10-9 9 4 1 x 10-4 1 x 10-10 10 3 1 x 10-3 1 x 10-11 11 2 1 x 10-2 1 x 10-12 12 1 1 x 10-1 1 x 10-13 13 0 1 x 100 1 x 10-14 14 NaOH, 0.1 M Household bleach Household ammonia Lime water Milk of magnesia Borax Baking soda Egg white, seawater Human blood, tears Milk Saliva Rain Black coffee Banana Tomatoes Wine Cola, vinegar Lemon juice Gastric juice More basic 7 1 x 10-7 1 x 10-7 7 More acidic

  20. Acid – Base Concentrations 10-1 pH = 3 pH = 11 OH- H3O+ pH = 7 10-7 concentration (moles/L) H3O+ OH- OH- H3O+ 10-14 [H3O+]<[OH-] [H3O+]>[OH-] [H3O+]=[OH-] acidic solution neutral solution basic solution Timberlake, Chemistry 7th Edition, page 332

  21. pH pH = -log [H+] pOH = -log [OH-] pH + pOH = 14 Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 285

  22. Self-Ionization Of Water Even the purest of water conducts electricity. This is due to the fact that water self-ionizes, that is, it creates a small amount of H3O+ and OH-. H2O + H2O H3O+ + OH- In pure water, the concentration of H+ is always equal to the concentration of OH-. This equilibrium is very important because it creates a concentration of H+ whose negative logarithm is 7, the pH of a neutral solution.

  23. pH and pOH • pH = - log[H3O+] [H3O+] = 10-pH pOH = - log[OH-] [OH-] = 10-pOH • pH + pOH = 14.00 • neutral solution: [H3O+] = [OH-] = 10 –7 M pH = 7.0 acidic solution: [H3O+] > 10-7 M pH < 7.0 basic solution: [H3O+] < 10-7 M pH > 7.0

  24. Practice Problems: Calculate the pH and pOH of: 3.2 x 10-6 M HCl 2.5 x 10-8 M NaOH Calculate the molarity of: HNO3 pH = 5.75 5 g HNO3 in 800 mL solution. HCl pOH = 11.3 pH = 5.5 pOH = 8.5 pOH = 7.6 pH = 6.4 1.8 x 10-6 M 0.099 M 0.002 M

  25. Strengths of Acids and Bases Strong acid: Completely ionizes to produce H+ Weak acid: Only partly ionizes Strong base: Completely dissolves to produce OH- Weak base: Only partly dissolves

  26. HCl hydrochloric acid HNO3 nitric acid H2SO4 sulfuric acid HBr hydrobromic acid HI hydroiodic acid HClO4 perchloric acid Strong Acids LiOH lithium hydroxide NaOH sodium hydroxide KOH potassium hydroxide RbOH rubidium hydroxide CsOH cesium hydroxide *Ca(OH)2 calcium hydroxide *Sr(OH)2 strontium hydroxide *Ba(OH)2 barium hydroxide Strong Bases * These bases completely dissociate in solutions of 0.01 M or less. The other bases make solutions of 1.0 M and are 100% dissociated at that concentration. There are other strong bases than those listed, but they are not often encountered.

  27. Strength vs. Concentration Acids and bases: Strong acids and bases can be concentrated or dilute Weak acids and bases can be concentrated or dilute Strength is how well the acid or base produces ions Strong = complete ionization Weak = partial ionization Concentration is how many ions are in a volume Concentrated = many ions in a volume Weak = few ions in a volume

  28. Your turn! • Complete exercise C.9 (Strong vs Concentrated) found on pages 376-377 (Due next class for a Lab grade) • Complete pH and pOH worksheet (Due next class for a homework grade.)

  29. Questions ?

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