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Chapter 16

Chapter 16. Acids- Base Titration and pH. Section 16.1. Aqueous Solutions and the Concept of pH. Self Ionization of Water. When two molecules of water produce a hydronium and hydroxide ion by the transfer of a proton. H 2 O + H 2 O   H 3 O + + OH -.

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Chapter 16

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  1. Chapter 16 Acids- Base Titration and pH

  2. Section 16.1 Aqueous Solutions and the Concept of pH

  3. Self Ionization of Water • When two molecules of water produce a hydronium and hydroxide ion by the transfer of a proton. • H2O + H2O  H3O+ + OH-

  4. At 25C the [H3O+] = [OH-]= 10-7 M • So, the products of [H3O+] and [OH-] can be represented by: • [H3O+] x [OH-] • 10-7 M x 10-7 M = 10-14 M2 • Where 10-14 M2 Is the Kw ( ionization constant of water) So, [H3O+] x [OH-]= Kw at 25C

  5. Neutral, Acidic, and Basic Solutions • Neutral solutions: [H3O+] = [OH-]= 10-7 M • Acidic solutions: [H3O+] > [OH-] • Basic solutions: [H3O+] < [OH-]

  6. Calculating the [H3O+] and [OH-] • We can find the [H3O+] and[OH-] by using the formula: • [H3O+] x [OH-]= Kw= 10-14 M2 Practice p: 484

  7. The pH Scale • It is the negative logarithm of the hydronium ion concentration • pH= - log [H3O+]

  8. Likewise, pOH It is the negative logarithm of the hydroxide ion concentration • pOH= - log [OH-] • So, pH + p OH= 14 at 25C

  9. Calculations Involving pH • [H3O+]=10-pH • Practice p: 487

  10. Summary: • 1- [H3O+] x [OH-]= Kw • 2- pH= - log [H3O+] • 3- pOH= - log [OH-] • 4- pH + p OH= 14 at 25C • 5- [H3O+]=10-pH

  11. Section 16.2 Determining pH and Titrations

  12. Indicators and pH Meters • 1- Acid- Base indicators: are compounds whose colors are sensitive to pH. Indicators come in many different colors. The exact pH range over which an indicator changes color also varies.

  13. 2-Universal indicators: the pH of solution can be determined by comparing the color it turns with the scale of paper.

  14. 3- pH meter: determines the pH of a solution by measuring the voltage between the electrodes that are placed in the solution. (It’s the most accurate way to determine the pH)

  15. Titration • Is the controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration. • The equation of titration is: • H3O+ + OH-  2H2O

  16. Types of Titration • 1- strong acid- strong base • 2- strong acid- weak base • 3- weak acid- strong base

  17. Indicators are specific, each type of titration needs a specific indicator • For example: • Strong acid- strong base titration: We use bromothymol blue (6.2- 7.6) • For strong acid- weak base titration: We use bromophenol blue ( 3-4.6) • For weak acid- strong base titration We use phenolphtalein(8-10)

  18. Equivalence Point • The point at which the two solutions used in a titration are present in chemically equivalent amounts is called the equivalence point.

  19. End Point • The endpoint in titration marks the point at which the color of indicator changes.

  20. Titration setup

  21. Titration Curves

  22. Molarity and Titration • The solution that contains precisely known concentration of solute is known as the standard solution. • To find the molarity or the volume of an unknown solution we use the equation: • No of moles of acid= No of moles of base • CxV (acid)= CxV (base) • Practice p: 503 (1 and 2)

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