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Acids

Acids . Bases. Acids. Taste sour Form solution that conduct electricity React with metals Turn blue litmus paper to red React with bases to form salt and water Ex: fruit juice, vinegar, milk. Bases. Form solutions that conduct electricity Slippery or soapy in the skin Taste bitter

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Acids

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  1. Acids Bases

  2. Acids • Taste sour • Form solution that conduct electricity • React with metals • Turn blue litmus paper to red • React with bases to form salt and water • Ex: fruit juice, vinegar, milk

  3. Bases • Form solutions that conduct electricity • Slippery or soapy in the skin • Taste bitter • Turn red litmus paper to blue • Reacts with acids to form salt and water • Ex: soap, shampoo, cleaning agent

  4. Arrhenius Theory • By Svante August Arrhenius • Acids form hydrogen ion(H+) in aqueous solutions • Bases form hydroxide ion (OH-) in aqueos solution • Ex: HCl(g)-----> H+(aq) + Cl-(aq) KOH -----> K+ + OH-(aq)

  5. Bronsted-Lowry Denition • By Johannes Bronsted and Thomas Lowry • Acid is a proton donor • Base is a proton acceptor • Ex: • HCl + H2O ---> H3O + Cl- • NH3 + H2O 

  6. Bronsted-Lowry Definition • The general reaction when an acid is dissolved in water is best represented by an acid donating H+ to water molecule to form a new acid (conjugate acid) and a new base( conjugate base) acid base conjugate Conjugate . Acid base • HA(aq) + H20(l) ----> H3O+(aq) + A-(aq)

  7. Ex: HCl + H2O ---> H3O+ + Cl- acid base conjugate conjugate acid base

  8. Identify the acid and the base in the following reactions: • HSO4- + PO43- ---> HO42- + SO42- • HNO3 + H2O ---> H3O + + NO3- • H3PO4 + CN- ---> H2PO4- + HCN • Answers Acid base • HSO4- PO43- • HNO3 H2O • HCN H2PO4-

  9. Conjugate Acid-base pair • Consists of two substances related to each other by donating and accepting of a single proton Acid-conjugate base pair Ex: HCl(aq) + H2O(l)  H3O+ + Cl- Base-conjugate acid pair H3O+ --> hydronium ion

  10. Which of the following represent Conjugate acid-base pair? • A) HF, F- • B) NH4+, NH3 • C) HCl, H2O • Answer A and B are conjugate acid base pair because they differ by one H+ C is not because the conjugate acid-base pair of HCl is Cl-

  11. Writing Conjugate Bases • Write the conjugate base for each of the following: • a) HClO4 HClO4 ----> H+ ClO4- conjugate base • b) H3PO4 H3PO4 H+ H2PO4 conjugate base

  12. Practice: Classwork Which of the following represent conjugate acid-base pair? A) HClO4, ClO4- B) HCl, ClO- C) H2PO4-, HPO42- D) HNO3, NO3- Write the conjugate base for each of the ff: • H2S • NH3 • H2SO3

  13. Answer Which of the following represent conjugate acid-base pair? A) HClO4, ClO4- B) HCl, ClO- C) H2PO4-, HPO42- D) HNO3, NO3- Write the conjugate base for each of the ff: • H2S  HS- • NH3  NH2- • H2SO3 HSO3-

  14. Lewis Theory • Gilbert Lewis • Chemical reactions involve the arrangement of the valence electrons of an atom. • Acid is an electron pair acceptor • Base is an electron pair donor • H2O + NH3 • H H + H-O-H + : N H ---> H-N-H + OH- H H Lewis Acid Lewis Base

  15. Ex: reaction between BCl3 and NH3 Cl H Cl H Cl – B + : N –H ---> Cl –B – N –H ClH Cl H Lewis Lewis Lewis acid-base acid base adduct Adduct is the term used for the product of the Lewis Acid-base reaction

  16. Strengths of Acids and Bases

  17. Strong Acids • Bronsted-Lowry definition is useful in describing the strength of an acid • Strong acid is one that dissociates or ionizes completely in water • Ex:HCl + H2O  H3O+ + Cl- • Forward reaction predominates which indicates ionization is complete • Strong acid contains a weak conjugate base weaker than water

  18. Weak Acid • It does not completely dissociate or ionize. • Ex: Acetic Acid( CH3COOH) • CH3COOH + H2O H30+ + CH3COO- acetate ion • The two arrows indicate that the ionization is not complete • The reverse reaction predominates that means only few ions are dissociated • Weak acid contains relatively strong conjugate base

  19. Strong Bases • Common strong bases are those that contain the hydroxide ion • Ex:,NaOH,KOH Mg(OH)2, Ca(OH)2 Ba(OH)2 • Very soluble in water

  20. Weak Bases • The strengths of bases that do not have OH- are described in the same way that the strengths of the acids were described • Weak base does not completely dissociate in water • Ex: NH3 + H2O NH4+ + OH- reverse reaction predominates

  21. Show the ionization of H2SO4 and NaOH H2O H2SO4(l) ----> H+(aq) + SO42-(aq) 2H+(aq) + SO42-(aq) H2O NaOH ------> Na+ + OH-

  22. Acid Strength

  23. Water as an acid and a base • Amphoteric substance  A substance that can behave either as an acid or a base • Ionizaton of water • H2O(l) + H2O(l) ---> H3O+(aq) + OH-(aq) • The forward reaction is not great • In pure water only a tiny amount of H3O+ and OH- is present. • [H3O+] = [OH-] = 1.0x10-7M

  24. The product of the H3O+ and OH- concentrations is always constant at 250C [H3O] [OH-] = 1x 10 -14 (1x 10-7 ) ( 1 x 10-7) = 1 x 10-14 This is called the ion product constant of water ( Kw) • Note the product of H3O and OH- in any aqueous is constant which means when [OH-] goes up the [H3O] must go down • Acidic solution  [H+] > [OH-] • Basic solution  [ H+] < [OH-] • Neutral solution  [H+] = [OH-]

  25. Ex : calculate [H+] or [OH-] as required for each of the following at 250C and state whether the solution is acidic, basic and neutral • A) 1.0x10-5M OH- Given: [OH-] = 1x10-5 Find: H+ Solution: [H+] [OH-] = 1x10-14 [H+] = 1x10-14 [OH-] [H+] = 1 x 10-14 [ 1x10-5] = 1x 10-9 M Since OH- = 1x10-5M H+ = 1x10-9M The solution is basic since OH- > H+

  26. b) 10.0M H+ • Find: OH- Solution: [H+][OH-] = 1 x10-14 [OH-] = 1x 10-14 10.0M = 1x 10-15M [OH-] = 1x10-15 [H+] = 1x 101M [H+] > [OH-] = the solution is acidic

  27. 1. Which is greater [OH-] or [H+] , if [H+]= 2.8x 10-5M an aqueous solution at 250C? 2. How many times greater is [OH-] than [H+] if [H+] = 1.0x 10-9 M in aqueous solution at 250C? 3. Calculate the [H+] or [OH-] as required for each of the following at 250C and state whether the solution is neutral, acidic or basic. • [H+] = 3.4 x 10-4M • [H+] = 2.6x 10-8M • [OH-] = 6.2 x 10-9M

  28. The pH Scale Was proposed by Soren Sorensen ( Danish biochemist) • pH means power of hydrogen • Has a range from 0 to 14 and is logarithmic which means that each step is ten times the previous Ex: pH of 5 is ten times more acid than 6 What about pH 5 and 7 ---> pH 5 is 100times more acid than 7 What about pH 5 and 8?  1000 times acidic

  29. pH scale • 0-most acidic and 14 is most basic 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 • At pH-7, water has equal amount of H+ and OH- ions [H+] = [OH-]  neutral [H+] > [OH-] acidic [H+] < [OH-] basic

  30. pH of a solution • Defined is the negative of the logarithm of the hydronium ion concentration, [H3O+] pH = - log [H3O+] Ex: Pure water has [H3O+]= 1x10-7M. Find pH pH = -log[H3O+] pH = -log[ 1x10-7M] pH = - (-7) pH = 7

  31. In Basic solution, [OH-] can be expressed as pOH • pOH = -log [OH-] Recall that [H3O+] [OH-] = 1 x 10 -14 Using the definition of pH and pOH the equation can be translated as pH + pOH = 14 In summary, pH= -log[H3O+] pOH = -log [OH-] [H3O+][OH-] = 1x10-14 pH + pOH = 14

  32. In Pure water, the concentrations of H3O+ and OH- are equal [H3O+] = [OH-] = 1x10-7M thus pH and pOH are also equal pH = pOH = 7 pH + pOH = 14 7 + 7 = 14

  33. Ex: • Find the pH and pOH of 0.001MHCl solution • Given: [H3O+] = 0.001M • Find a) pH b) pOH • Solution • A) pH = -log [H3O+] • = -log [ 1x10-3] = -(-3) • = 3 • B) pH + pOH = 14 • pOH = 14 - pH • = 14 - 3 • 11

  34. Ex2: • If the OH- is equal to 0.00001M, Find the pH Solution: Get the pOH first pOH=-log[OH-] = -log(10-5M) = -(-5) pOH = 5 Get the pH pH +pOH = 14 pH = 14 – pOH = 14 – 5 pH = 9

  35. Class work • A solution has a H3O+ concentration equal to 5.5x 10-8M. What is the pH of the solution? • The pH of rainwater in a locality is 3. What is the [H3O+]? • What is the [H+] of a solution with a pH of 4.2? • The pOH of blood is 6.6. What is the pH of the blood? • Calculate the pH and pOH for each of the ff. • A) a solution in which[H+] = 3.6 x 10-9M • B)[OH-] = 9.2 x 10-2M • The pH of the solution is 5.67. What is the pOH of the solution?

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