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SURVEY OF CHEMISTRY I CHEM 1151 CHAPTER 9

SURVEY OF CHEMISTRY I CHEM 1151 CHAPTER 9. DR. AUGUSTINE OFORI AGYEMAN Assistant professor of chemistry Department of natural sciences Clayton state university. CHAPTER 9 ACIDS, BASES, AND SALTS. ARRHENIUS ACIDS. - Acids are substances that ionize in aqueous solutions to

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SURVEY OF CHEMISTRY I CHEM 1151 CHAPTER 9

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  1. SURVEY OF CHEMISTRY I CHEM 1151CHAPTER 9 DR. AUGUSTINE OFORI AGYEMAN Assistant professor of chemistry Department of natural sciences Clayton state university

  2. CHAPTER 9 ACIDS, BASES, AND SALTS

  3. ARRHENIUS ACIDS - Acids are substances that ionize in aqueous solutions to produce hydrogen ions (proton, H+) HCl, HNO3, H2SO4 HCl(aq) → H+(aq) + Cl-(aq) HNO3(aq) → H+(aq) + NO3-(aq) Ionize: dissolving in solution (water) to form ions - Arrhenius acids are covalent compounds in the pure state Properties sour taste, change blue litmus paper to red, corrosive

  4. ARRHENIUS BASES - Bases are substances that ionize in aqueous solutions to produce hydroxide ions (OH-) NaOH, KOH, Ca(OH)2 NaOH → Na+(aq) + OH-(aq) Ca(OH)2 → Ca2+(aq) + 2OH-(aq) - Arrhenius bases are ionic compounds in the pure state Properties bitter taste, change red litmus paper to blue, slippery to touch

  5. BRONSTED-LOWRY ACIDS - Acids are proton (H+) donors - Not restricted to aqueous solutions HCl, HNO3, H2SO4

  6. BRONSTED-LOWRY BASES - Bases are proton acceptors - Not restricted to aqueous solutions NH3, dimethyl sulfoxide (DMSO) - Proton donation cannot occur unless an acceptor is present

  7. LEWIS ACIDS - Acids are electron pair acceptors - Not restricted to protons or aqueous solutions BF3, B2H6, Al2Cl6, AlF3, PCl5

  8. LEWIS BASES - Bases are electron pair donors - Not restricted to protons or aqueous solutions NH3, ethers, ketones, carbon monoxide, sulfoxides

  9. ACIDS Monoprotic Acid - Donates one proton per molecule (HNO3, HCl) Diprotic Acid - Donates two protons per molecule (H2SO4, H2CO3) Triprotic Acid - Donates three proton per molecule (H3PO4, H3AsO4) Polyprotic Acid - Donates two or more protons per molecule

  10. CONJUGATE ACID BASE PAIRS - Most Bronsted-Lowry acid-base reactions do not undergo 100% conversion - Acid-base equilibrium is established - Every acid has a conjugate base associated with it (by removing H+) - Every base has a conjugate acid associated with it (by adding H+)

  11. CONJUGATE ACID BASE PAIRS HX(aq) + H2O(l) X-(aq) + H3O+(aq) - HX donates a proton to H2O to form X- HX is the acid and X- is its conjugate base - H2O accepts a proton from HX H2O acts as a base and H3O+ is its conjugate acid

  12. CONJUGATE ACID BASE PAIRS NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) HNO3(aq) + H2O(l) H3O+(aq) + NO3-(aq) HF(aq) + H2O(l) H3O+(aq) + F-(aq)

  13. AMPHOTERIC SUBSTANCES - A substance that can lose or accept a proton - A substance that can function as either Bronsted-Lowry acid or Bronsted-Lowry base - H2O is the most common (refer to previous slide for examples)

  14. AUTOPROTOLYSIS OF WATER - Self ionization - Pure water molecules (small percentage) interact with one another to form equal amounts of H3O+ and OH- ions Kw H2O(l) + H2O(l) H3O+(aq) + OH-(aq) reduces to Kw H2O(l) H+(aq) + OH-(aq)

  15. AUTOPROTOLYSIS OF WATER - The number of H3O+ and OH- ions present in a sample of pure water at any given time is small - At equilibrium (25oC) [H3O+] = [OH-] = 1.00 x 10-7 M - [H3O+] = hydronium ion concentration - [OH-] = hydroxide ion concentration

  16. AUTOPROTOLYSIS OF WATER - The ion product constant of water = [H3O+] x [OH-] = (1.00 x 10-7) x (1.00 x 10-7) = 1.00 x 10-14 - Valid in all solutions (pure water and water with solutes)

  17. AUTOPROTOLYSIS OF WATER Addition of Acidic Solute - increases [H3O+] - [OH-] decreases by the same factor to make product 1.00 x 10-14 Addition of Basic Solute - increases [OH-] - [H3O+] decreases by the same factor to make product 1.00 x 10-14

  18. STRENGTH OF ACIDS Strong Acids - Transfer 100% (or very nearly 100%) of their protons to H2O in aqueous solution - Completely or nearly completely ionize in aqueous solution - Strong electrolytes HCl, HNO3, H2SO4 Weak Acids - Transfer only a small percentage (< 5%) of their protons to H2O in aqueous solution Organic acids: acetic acid, citric acid

  19. STRENGTH OF BASES Strong Bases - Completely or nearly completely ionize in aqueous solution - Strong electrolytes Hydroxides of Groups IA and IIA are strong bases LiOH, CsOH, Ba(OH)2, Ca(OH)2 most common in lab: NaOH and KOH Weak bases - produce small amounts of OH- ions in aqueous solution methylamine, cocaine, morphine most common: NH3

  20. THE pH CONCEPT pH - Negative logarithm of the hydronium ion concentration [H3O+] in an aqueous solution - [H3O+] and [H+] are used interchangeably pH = - log[H3O+] Or pH = - log[H+]

  21. THE pH CONCEPT Acidic Solution - An aqueous solution in which [H3O+] is higher than [OH-] (pH is less than 7.0) Basic Solution - An aqueous solution in which [OH-] is higher than [H3O+] (pH is greater than 7.0) Neutral Solution - An aqueous solution in which [H3O+] is equal to [OH-] (pH is equal to 7.0) - Increasing [H3O+] lowers the pH

  22. THE pH CONCEPT - For [H3O+] coefficient of 1.0 - Expressed in exponential notation - The pH is the negative of the exponent value [H3O+] = 1.0 x 10-5 M, then pH = 5.0 [H3O+] = 1.0 x 10-3 M, then pH = 3.0 [H3O+] = 1.0 x 10-11 M, then pH = 11.0

  23. THE pH CONCEPT - A change of 1 unit in pH corresponds to a tenfold change in [H3O+] pH = 3.0 implies [H3O+] = 1.0 x 10-3 M = 0.0010 M pH = 2.0 implies [H3O+] = 1.0 x 10-2 M = 0.010 M which is tenfold - The pH meter and the litmus paper are used to determine pH values of solutions

  24. ACID-BASE REACTIONS - Neutralization reactions - Occurs when a solution of an acid is mixed with a solution of a base - The products are salt and water when the base is a metal hydroxide HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) HNO3 (aq) + KOH(aq) → KNO3(aq) + H2O(l) - These reactions can be viewed as proton transfer reactions or double-replacement reactions - H+ and OH- ions always react in a one-to-one ratio to form water

  25. SALTS - A cation from a base combines with an anion from an acid to form a salt (A reaction between an acid and a hydroxide base) - Salts are ionic compounds - The positive ion is a metal or polyatomic ion - The negative ion is a nonmetal or polyatomic ion [exception is the hydroxide ion (OH-)] - Salts dissociate completely into ions in solution (strong electrolytes)

  26. BUFFER SOLUTION - A mixture of a conjugate acid-base pair - Tends to resist changes in pH upon addition of an acid or a base - The resistive action is the result of equilibrium between the weak acid (HA) and its conjugate base (A-) HA(aq) + H2O(l) → H3O+(aq) + A-(aq) - Commonly used in biological systems - Enzyme-catalyzed reactions depend on pH

  27. BUFFER SOLUTION Examples HC2H3O2/C2H3O2- HF/F- NH3/NH4+ H2CO3/HCO3-

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