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Introduction to Acids and Bases

Introduction to Acids and Bases. Chapter 19. What is and Acid?. Arrhenius Acid Defined as any chemical that increases the concentration of hydrogen ions (H + )in solution. (usually by a dissociation reaction Examples Hydrochloric acid HCl  H + + Cl -

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Introduction to Acids and Bases

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  1. Introduction toAcids and Bases Chapter 19

  2. What is and Acid? • Arrhenius Acid • Defined as any chemical that increases the concentration of hydrogen ions (H+)in solution. (usually by a dissociation reaction Examples • Hydrochloric acid HCl  H+ + Cl- • Sulfuric acid H2SO4 2H+ + SO42- • Phosphoric acid H3PO4 3H+ + PO43-

  3. Not all Hydrogens are acidic • The hydrogen must be part of a polar bond in order to dissociate. • For example: • HF is acidic, but CH4 is not. • In CH4, the hydrogen is part of a non-polar covalent bond and does not dissociate in solution! • HF is a polar bond and HF  H+ + F-

  4. Bronsted – Lowry Acid • Defined as a molecule or ion that is a hydrogen ion donor. • Also known as a proton donor because H+ is a proton. • The acid will donate its H+ ion to a base in an acid base reaction. H+ + OH- H2O Acid + Base

  5. What is a Base? • Arrhenius Base • Defined as any chemical that increases the hydroxide ions (OH-) concentration in solution. • Examples- • NaOH  Na+ + OH- • KOH  K+ + OH- • Ca(OH)2  Ca2+ + 2OH-

  6. Bronsted-Lowry Base • Defined as a hydrogen ion acceptor. • In an acid-base reaction the base “accepts” the hydrogen ion from the acid. NH3 + H+ NH4+ NH3accepts the H+ from the acid.

  7. Physical Properties of Acids • Taste Sour • Feel Sticky • React with metals to produce hydrogen gas • Conduct electricity – because they produce ions in solution • Are corrosive (they can burn skin and other materials) • Are found in many naturally colored solutions • Turn Litmus Indicator Red

  8. Physical Properties of Bases • Taste Bitter • Feel slippery or soapy • Also conduct electricity • Rarely found in colored solutions • Most do not have a smell (except ammonia) • Turn Litmus indicator Blue • Turn Phenolphthalein Indicator Pink

  9. Physical Properties of Neutral Compounds • Do not taste bitter or sour, but rather have a sweet or oily taste, or no taste at all. • Many feel like water, or feel greasy/ oily • May or may not conduct electricity • They have varied reactivities. • Many have a strong chemical smell or no smell at all.

  10. Using pH to identify Acids and Bases The pH Scale

  11. What is pH? • pH = -log [H+] pH= -log[H3O+] • pH stands for the “power of the hydrogen ion.” • It is based on a logarithmic scale which has a base power of 10. • A pH of 1 differs from a pH of 2 by a factor of 10.

  12. pH Scale - Continued • Created to express acidity as a more simple number than molarity. • pH = - log [H+] • If . . . • [H+] = 1 x 10-7 then pH = 7 (neutral) • [H+] = 1 x 10-3 then pH = 3 (acid) • [H+] = 1 x 10-10 then pH = 10 (base)

  13. Why is the pH scale 0 – 14? The Self-Ionization of Water H2O (l) ↔ H+ (aq) + OH-(aq) • The equilibrium expression for this reaction is • Kw = [H+][OH-] = 1 x 10-14 • This low equilibrium constant means very few water molecules ionize.

  14. Water is considered neutral because in water • [H+] = [OH-] = 1 x 10-7 M • pH = -log (1 x 10-7 ) = 7 • *All aqueous solutions have H+ and OH- ions • Acids HCl  H+ + Cl- • Acidic solutions increases the H+ concentration and [H+] > [OH-] • Bases NaOH  Na+ + OH- • Basic solutions increases the OH- concentration and [H+] < [OH-]

  15. pH scale ranges from 0-14 • pH<7 indicates an acidic solution • pH=7 indicates a neutral solution • pH>7 indicates a basic solution • Strong Acids have pH of 0 or 1 • Strong Bases have a pH of 13 or 14

  16. Strength of Acids and Bases“Strength” refers to how much an acid or base ionizes in a solution.

  17. Strengths of Acids and Bases

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