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Characteristics of Acids & Bases

Characteristics of Acids & Bases. Characteristics of acidic and basic solutions, and identify the ions responsible for these properties. Acids are generally a class of substances that taste sour, such as vinegar, which is a dilute solution of acetic acid.

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Characteristics of Acids & Bases

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  1. Characteristics of Acids & Bases Characteristics of acidic and basic solutions, and identify the ions responsible for these properties. Developed by JM Ingalls

  2. Acids are generally a class of substances that taste sour, such as vinegar, which is a dilute solution of acetic acid. Bases, or alkaline substances, are characterized by their bitter taste and slippery feel. Acids and Bases Developed by JM Ingalls

  3. First precise definition of an an acid and base was given by Swedish Chemist Svante Arrhenius. Referred to as Arrhenius Theory. Swedish chemist Arrhenius defined an acid as a substance that ionizes in water to give hydrogen ions, and a base as a substance that ionizes in water to give hydroxide ions. The Proton in Water: Arrhenius Theory Developed by JM Ingalls

  4. Arrhenius Theory • Hydrochloric acid, HCl, is a strong acid, and is very soluble in water. It dissociates into its component ions in the following manner: • HCl (g) H+ (aq) + Cl- (aq) Developed by JM Ingalls

  5. Arrhenius Theory • Hydrogen ion interacts strongly with a lone pair of electrons on the oxygen of a water molecule. • Resulting ion, H3O+ is called the hydronium ion. Developed by JM Ingalls

  6. Hydronium ion H+ + H-O-H H3O+ ACIDIC solutions are formed when an acid transfers a proton to water Developed by JM Ingalls

  7. The reaction of HCl with water • HCl (aq) + H2O (l) H3O+ (aq) + Cl- (aq) • HCl (aq) H+ (aq) + Cl- (aq) Developed by JM Ingalls

  8. Brønsted-Lowry Concept of Acids and Bases • Acids are substances that are capable of donating a proton, and bases are substances capable of accepting a proton. • http://www.science.ubc.ca/~chem/tutorials/pH/section0/hcl.html Developed by JM Ingalls

  9. Brønsted-Lowry Concept Proton transfer from Chloride Ion to Water Molecule http://www.science.ubc.ca/~chem/tutorials/pH/index.html Developed by JM Ingalls

  10. Brønsted-Lowry Concept • Water can act as an acid or a base. • NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) Developed by JM Ingalls

  11. Brønsted-Lowry Concept • H2O acts as a Brønsted acid by donating a proton to NH3 which acts as a Brønsted base. • All Arrhenius acids are also Brønsted acids.All Arrhenius bases are also Brønsted bases. Developed by JM Ingalls

  12. Conjugate Acid-Base Pairs • Reaction of NH3 and H2O : (1) NH3 + H2O NH4+ + OH- • Reverse of this reaction: (2) NH4 + OH- NH3 + H2O • NH4+ acts as an acid which donates a proton to OH-. OH- acts as a base Developed by JM Ingalls

  13. Conjugate Acid-Base Pairs • An acid and a base that are related by the gain and loss of a proton are called: • conjugate acid-base pair Developed by JM Ingalls

  14. NH4+ is the conjugate acid of NH3 Every acid has associated with it a conjugate base. NH3 is the conjugate base of NH4+. Every base has associated with it a conjugate acid Conjugate Acid-Base Developed by JM Ingalls

  15. Conjugate Acid-Base base acid conj conj acid base • NH3 + H2O NH4+ + OH- Developed by JM Ingalls

  16. Conjugate Acid-Base • Acids and bases can be either neutral or charged species: H2O (acid or base, neutral), O2- (base, charged), C2H3O2- (acid, charged) . Developed by JM Ingalls

  17. Conjugate Acid-Base • For any reaction: HA + H2O H3O+ + A- • If HA is a strong acid because it gives up its proton readily, then A- is a weak base because it has little affinity for the proton. Developed by JM Ingalls

  18. Conjugate Acid-Base HA + H2O H3O+ + A- • If HA is a weak acid because it donates very few protons to the water, then A- has a high affinity for a proton, and A- is a stronger base than water. Developed by JM Ingalls

  19. Neutralization Reactions • In a Neutralization reaction a strong acid will react a strong base to yield a salt and water: • Ca(OH)2 + HNO3 Ca(NO3)2 + H2O Developed by JM Ingalls

  20. Lewis acid and Lewis base • Neither the Arrhenius or the Brønsted-Lowry theory of acids and bases accounts for all the existing acids and bases. A new definition of acid-base behavior, called Lewis theory, is more comprehensive. Developed by JM Ingalls

  21. Lewis acid and Lewis base • A Lewis acid is an electron-pair acceptor. • A Lewis base is an electron-pair donor. Developed by JM Ingalls

  22. Lewis acid and Lewis base • Everything that is a Brønsted-Lowry base (a proton acceptor) is also a Lewis base. • Lewis bases can donate their electrons to substances other than H. Developed by JM Ingalls

  23. Lewis acid and Lewis base H H + H+ + :N- H H-N-H H H • NH3 is a Brønsted-Lowry base and a Lewis base Developed by JM Ingalls

  24. Lewis acid and Lewis base H F H F H-N: + B-F H-N-B-F H F H F Base Acid • Here, NH3 is behaving as a Lewis base only (and BF3 is a Lewis acid). Developed by JM Ingalls

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