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To learn about two models of acids and bases

Objectives 16.1 Properties of Acids and Bases. To learn about two models of acids and bases To understand the relationship of conjugate acid-base pairs To understand the concept of acid strength

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To learn about two models of acids and bases

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  1. Objectives 16.1 Properties of Acids and Bases • To learn about two models of acids and bases • To understand the relationship of conjugate acid-base pairs • To understand the concept of acid strength • To understand the relationship between acid strength and the strength of the conjugate base • To learn about the ionization of water

  2. A. Acids and Bases • The Arrhenius Model • Acid – produces hydrogen ions in aqueous solution • Base – produces hydroxide ions in aqueous solution

  3. A. Acids and Bases • The Bronsted-Lowry Model • Acid – proton donor • Base – proton acceptor • The general reaction for an acid dissolving in water is

  4. A. Acids and Bases • The Bronsted-Lowry Model • Conjugate acid-basepair

  5. A. Acids and Bases • The Bronsted-Lowry Model • Water acts as a base accepting a proton from the acid. • Forms hydronium ion (H3O+)

  6. B. Acid Strength • Strong acid – completely ionized or completely dissociated

  7. B. Acid Strength • Weak acid – most of the acid molecules remain intact

  8. B. Acid Strength • A strong acid contains a relatively weak conjugate base.

  9. B. Acid Strength • Common strong acids are • Sulfuric acid, H2SO4 • Hydrochloric acid, HCl • Nitric acid, HNO3 • Perchloric acid, HClO4

  10. B. Acid Strength • Oxyacid – acidic proton is attached to an oxygen atom • Organic acid – have a carbon atom backbone and commonly contain the carboxyl group • Typically a weak acid

  11. B. Acid Strength

  12. C. Water as an Acid and a Base • Water is amphoteric – it can behave as either an acid or as a base • Ionization of water • Concentration of hydronium and hydroxide are equal

  13. C. Water as an Acid and a Base • Product of [H3O+] and [OH] is always constant.

  14. C. Water as an Acid and a Base

  15. Objectives 16.2 Determining the Acidity of a Solution • To understand pH and pOH • To learn to find pH and pOH for various solutions • To use a calculator to find pH • To learn methods for measuring pH of a solution • To learn to calculate the pH of strong acids

  16. A. The pH Scale • The “p scale” is used to express small numbers. • pH = log [H+]

  17. A. The pH Scale

  18. A. The pH Scale • Because the pH scale is a log scale based on 10, the pH changes by 1 for every power of 10 change in the [H+].

  19. A. The pH Scale

  20. A. The pH Scale • pOH scale • pOH = log [OH] • pH + pOH = 14.00

  21. A. The pH Scale

  22. B. Measuring pH • Indicators – substances that exhibit different colors in acidic and basic solutions • In an acid solution the indicator will be in the HIn form. • In a basic solution the indicator will be in the In form.

  23. B. Measuring pH • Other methods • Indicator paper • pH meter

  24. C. Calculating the pH of Strong Acid Solutions • Determine the [H+]. • pH = log[H+]

  25. Objectives 16.3 Titrations and Buffers • To learn about acid-base titrations • To understand the general characteristics of buffered solutions

  26. A. Acid-Base Titrations • Titration – delivering a measured volume of a solution of known concentration into the solution being analyzed • Titrant – a standard solution • Buret – device used for accurate measurement of the delivery of a liquid • Stoichiometric point (equivalence point) – when just enough titrant has been added to react with all of the solution being analyzed

  27. A. Acid-Base Titrations • Titration curve (pH curve) – plot of the data (pH vs volume) for a titration

  28. B. Buffered Solutions • Buffered solution – resists a change in its pH when either and acid or a base has been added • Presence of a weak acid and its conjugate base buffers the solution

  29. B. Buffered Solutions

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