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IN THE NAME OF ALLAH THE MOST GRACIOUS, THE MOST MERCIFUL

IN THE NAME OF ALLAH THE MOST GRACIOUS, THE MOST MERCIFUL. CHEM 122. LEVEL-2 LECTURE# 2 CHAPTER 9 – ACIDS & BASES Chemistry by Timberlake p.266 RCDP. Presented by: Department Of Chemistry. Ionization of Water P-277. Occasionally, in water, a H + is transferred between H 2 O molecules

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IN THE NAME OF ALLAH THE MOST GRACIOUS, THE MOST MERCIFUL

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  1. IN THE NAME OF ALLAH THE MOST GRACIOUS, THE MOST MERCIFUL CHEM 122. LEVEL-2 LECTURE# 2CHAPTER 9 – ACIDS & BASES Chemistry by Timberlake p.266 RCDP • Presented by: • Department Of • Chemistry

  2. Ionization of Water P-277 Occasionally, in water, a H+ is transferred between H2O molecules . . . . . . . . H:O: + :O:H H:O:H + + :O:H- . . . . . . . . HH H water molecules hydronium hydroxide ion (+)ion (-)

  3. Pure Water is Neutral Pure water contains small, but equal amounts of ions: H3O+ and OH-, these are called ion product of water. H2O + H2O H3O+ + OH- hydronium hydroxide ion ion 1 x 10-7 M1 x 10-7 M H3O+ OH-

  4. Dissociation of water and Kw: Water itself is a very weak electrolyte. H2O + H2O ⇌ H3O+aq + OH-aq ( auto ionization ) Kc = [H3O+] [OH-] [H2O][H2O] This is calledequilibrium expression

  5. Ion Product of Water Kw [ ] means Molar concentration Kw = [ H3O+ ] [ OH- ] = [ 1 x 10-7 ][ 1 x 10-7 ] = 1 x 10-14

  6. H2O ⇌ H+ + OH- ( here H+ is called H3O+) Kw = [H3O+] [OH-] [H3O+] [OH-] = Mass action expression, is called ion product for water Kw is called Ion product constant for water or Ionization constant or Dissociation constant of water Kw = [H+] [OH-] (This equation is used to calculate molar concentrations of H+ and OH- ions in pure water) At equilibrium [H+] = [OH-] If; [H2O][H2O] =1 mol x 1 mol Kw = 1.0 x 10 -14 at 250C

  7. Acids • Increase H+ HCl (l) + H2O (l)H3O+(aq) + Cl-(aq) More [H3O+] than water: [H3O]> 1 x 10-7M As H3O+increases, OH-decreases [H3O+] > [OH-] H3O+ OH-

  8. Bases • Increase the hydroxide ions (OH-) H2O NaOH (s) Na+(aq) + OH- (aq) More [OH-] than water, [OH-] > 1 x 10-7M When OH- increases, H3O+ decreases [OH] > [H3O+] OH- H3O+

  9. Using Kw Q:The [OH- ] of a solution is 1.0 x 10- 3 M. What is the [H3O+]? Kw = [H3O+ ] [OH- ] = 1.0 x 10-14 [H3O+] = 1.0 x 10-14 [OH-] [H3O+] = 1.0 x 10-14 = 1.0 x 10-11 M 1.0 x 10- 3

  10. PH[P-279] • Indicates the acidity [H3O+] of the solution pH = - log [H3O+] From the French pouvoir hydrogene (“hydrogen power” or power of hydrogen)

  11. In the expression for [H3O+] 1 x 10-exponent the exponent = pH [H3O+] = 1 x 10-pH M

  12. The Concept of pHp279 -To specify the hydrogen ion concentration in a solution, we speak about pH. This is defined as, pH = log 1/ [H+] = - log [H+] -In a solution, if the hydrogen ion concentration is 10-3M . The pH of this solution is, pH = - log ( 10-3) = - ( -3 ) pH= 3 -If the hydrogen ion concentration is 10-8M, the pH will be “ 8“ -We already know that Kw = [H+] [OH-] thus, pKw = pH + pOH Since Kw = 1 x 10-14 , so pKw = 14.0 pH + pOH = 14.0 -In the neutral solution [H+] = [OH-] = 1.0 x 10-7 therefore pH = pOH = 7.0 pH for neutral solution = 7.0

  13. In acidic solution hydrogen ion concentration is greater than 1.0 x 10-7 M ( 1.0 x 10-1 to 1.0 x 10-6 M ) , it means pH is less than 7.0 i.e. from 1.0 to 6.0 In basic solution the hydrogen ion concentration is less than 1.0 x 10-7 M ( 1.0 x 10-8 to 1.0 x 10-10 M ), it means pH is more than 7.0 i.e. from 8.0 to 10.0 -The relationship of H+, OH-, pH, pOH at 250C, Kw=1.0x10-14 [H+][OH-]pHpOH Acidic solution > 1 x 10-7 < 1 x 10-7 < 7.0 > 7.0 Neutral solution = 1 x 10-7 = 1 x 10-7 = 7.0 = 7.0 Basic solution < 1 x 10-7 > 1 x 10-7 > 7.0 < 7.0 Substances having pH less than 7.0 are acidic , Lemon juice( citric acid ) Vinegar ( acetic acid ). Acids are sour in taste Substances having pH more than 7.0 are basic , Milk of magnesia ( a suspension of Mg (OH)2 ). Bases are bitter in taste.

  14. pH Range or scaleP-283 0 1 2 3 4 5 6 7 8 910 11 12 13 14 Neutral [H+]>[OH-][H+] = [OH-][OH-]>[H+] Acidic Basic

  15. Some [H3O+] and pH [H3O+] pH 1 x 10-5 M 5 1 x 10-9 M 9 1 x 10-11M 11

  16. pH of Some Common Acids • gastric juice 2.0 • lemon juice 2.3 • vinegar 2.8 • orange juice 3.5 • coffee 5.0 • milk 6.6

  17. pH of Some Common Bases • blood 7.4 • tears 7.4 • seawater 8.4 • milk of magnesia 10.6 • household ammonia 11.0

  18. Q: The pH of a soap is 10. What is the [H3O+] of the soap solution? Answer: [H3O+] = 1 x 10-pH M = 1 x 10-10 M

  19. Measuring pH and acid –base indicators : An indicatoris a weak organic acid or base, which on dissociation undergoes a change in color and this change in color depends on the pH of the solution. Acid form ⇌ H+ + Base form 1st. Color2nd. Color Litmus paper are of two types, (1).Pink (2). Blue (1). To test whether a solution is acidic, blue litmus paper is used. In acidic solution blue litmus paper turns pink. (2). To test whether a solution is basic, pink litmus paper is used. In basic solution pink litmus paper turns blue. For any accurate measurement of pH, a pH meter is used

  20. Acid – Base indicators

  21. Acid – Base indicators

  22. Equilibria Involving Weak Molecular Acids and Bases HA H+ + A- , Ka= [H+][A-] , pKa= - log Ka pKa for acetic acid = pKa = - log Ka = - log ( 1.8 x 10-5 ) = 4.74 BOH B+ + OH-, Kb=[B+][OH-], pKb = - log Kb pKb for pyridine = pKb = - log kb = - log ( 1.7 x 10-9)= 8.77

  23. The smaller the value of pka or pKb ,the stronger is the acid or base. For example Acetic acid , CH3-COOH , pka = 4.7 Chloroacetic acid, ClCH2-COOH, pKa = 2.85 Dichloroacetic acid, Cl2CH-COOH ,pKa = 1.30 The order of increasing acidity Acetic acid < Chloro acetic acid < Dichloro acetic acid

  24. Equilibria Involving Weak Molecular Acids and Bases • Percentage dissociation: For weak acid: HA H+ + A- For weak base: BOH OH- + B+ For 0.1 M acetic acid, [H+] = [A-]=1.3 x10 -3: Percentage dissociation = [A-] x 100 [HA] So, percentage dissociation of acetic acid = 1.3 x10 -3 x 100 = 1.3 % 0.1

  25. Equilibria Involving Weak Molecular Acids and Bases Dissociation of weak acids or bases is known by its percentage dissociation which is define as;

  26. Practicing questions • The pH of a 0.009300 molar solution of unknown monoprotic acid was measured and found to be 2.990. Calculate the percentage dissociation of this acid. • A weak acid, HA, has a Ka of 1 x 10-5.  If 0.100 mole of this acid is dissolved in one liter of water, the percentage of acid dissociated at equilibrium is closest to:a)   0.100%b)   1.00%c)   99.0%d)   99.9%e)   100%

  27. What is the pH of a solution that contains 1.00 x 10-4 M hydronium ion? • Calculate the [H3O+] of a solution that has a pH of 3.70. • Find the pH and pOH of a solution that contains 0.00350 M H3O+ ion. • Calculate the pH of a solution of NaOH if [OH]= 5x10-5 • Calculate the pH for a solution of HCl contains 0.2 M H3O+? • What is the pH of 0.2 M NaoH? IF Kb = 1x10-11 pH= 0.699 pH= 8.15

  28. Calculate [OH-] of a solution whose [H+] = 0.00375 M • Calculate the [H+] of a solution whose pH = 11.93 • Calculate the pOH of a solution whose [OH-] = 7.24 x 10-3 M • Calculate the pH of a solution whose pOH = 12.00 • Calculate the [H+] of a solution whose pOH = 8.00 • The acid ionization constant, Ka, for propanoic acid, C2H5COOH, is 1.3x10-5. • Calculate the hydrogen ion concentration, [H+], in a 0.20 molar solutionof propanoic acid. • Calculate the percentage of propanoic acid molecules that are ionized in the solution.

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