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Acid-Base Concepts

Acid-Base Concepts. Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology. Acid-Base Concepts. The definitions of an acid and a base range from proton and hydroxide donors to electron pair donors and acceptors to specialized definitions for non-solvent systems. .

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Acid-Base Concepts

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  1. Acid-Base Concepts Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

  2. Acid-Base Concepts The definitions of an acid and a base range from proton and hydroxide donors to electron pair donors and acceptors to specialized definitions for non-solvent systems.

  3. Acid-Base Definitions Arrhenius - Acids are proton donors, bases are hydroxide donors. Bronsted-Lowry - Acids are proton donors, bases are proton acceptors. Lux-Flood - Acids are oxide acceptors, bases are oxide donors.

  4. Lux-Flood ReactionsAcids are oxide acceptors, bases are oxide donors CaO + SiO2 CaSiO3 base acid CaO + H2O  Ca2+ + 2 OH- basic anhydride SiO2 + H2O  H2SiO3 acidic anhydride

  5. (CH3)4N+ Cl-+ FeCl3 (CH3)4N+ + FeCl4- OPCl3 or OP(OEt)3 Acid-Base DefinitionsDon’t Have To Be Limited to H & O (CH3)4N+ Cl- bases are chloride donors FeCl3 acids are chloride acceptors

  6. 2 H2O H3O+ + OH- 2 NH3 NH4+ + NH2- 2 OPCl3 OPCl2+ + OPCl4- strongest acid allowed in solvent strongest base allowed in solvent Solvent SystemsAutoionization

  7. 2 H2O H3O+ + OH- Solvent SystemsAcid Leveling acids stronger than H3O+ are leveled to H3O+ bases stronger than OH- are leveled to OH- HNO3 + H2O  H3O+ + NO3- CaO+ H2O  Ca2+ + 2 OH-

  8. 3 HF H2F+ + HF2- Solvent SystemsAcid Leveling What is the strongest acid and the strongest base allowed in liquid hydrofluoric acid?

  9. Other Acid-Base Definitions Lewis - Acids are electron pair acceptor, bases are electron pair donors. Usanovich - Acids are negative charge acceptors, bases are negative charge donors.

  10. nonmetal oxides are acidic metalloids are amphoteric metal oxides are basic General Acid-Base Concepts more basic

  11. BeO + 2 H+ Be2+ + H2O BeO + H2O + 2 OH- Be(OH)42- General Acid-Base Concepts Beryllium oxide is amphoteric high charge density causes polarization of any electron source BeO is more acidic and less basic than other alkaline earth oxides.

  12. Na++ n H2O [Na(H2O)n]+ General Acid-Base ConceptsHydration and Hydrolysis coordination of the solvent (solvation) releases energy and stabilizes the product high charge density ions have large hydration (solvation) energies

  13. H2O Al3++ 6 H2O [Al(H2O)6]3+ General Acid-Base ConceptsHydration and Hydrolysis If the cation is acidic enough, it can polarize the oxygen of water away from the hydrogen. the pH of 0.1 M Al(NO3)3 is 3.07 [Al(H2O)5 (OH)]2+ + H3O+ Why is 0.1 M iron(III) ion even more acidic?

  14. General Acid-Base ConceptsOxyacids HmXOn The acidity of oxyacids depends on formal charge on the central atom charge on the complex inductive effects of substituents

  15. HNO3 HClO3 HNO2 H3PO4 HSO4- H2PO4- HClO2 HClO General Acid-Base ConceptsOxyacids HmXOn if n-m  2, strong acid pKa << 0 = 1, weak acid pKa 2.1 ± 0.9 = 0, very weak acid pKa 8.5 ± 1 sequential proton loss leads to pK2 values of +5 greater Examples:

  16. HNO3 << 0 HClO3 HClO3 HNO2 3.3 H3PO4 2.1 HSO4- 1.9 H2PO4- 7.2 HClO2 HClO2 HClO 7.5

  17. General Acid-Base ConceptsOxyacids HmXOn The acidity of oxyacids depends on formal charge on the central atom charge on the complex inductive effects of substituents pKa = 10.5 - 5.0 n - x for X(OH)mOn

  18. General Acid-Base ConceptsOxyacids Special Cases H2SO3 pKa = 1.81 H3PO3 pKa = 2.00 H2CO3 pKa = 6.37 H3BO3 pKa = 9.1

  19. General Acid-Base ConceptsSubstituted Amines NR3 The basicity of amines depends on inductive effects of substituents steric effects pKb NF3 NH3 NH2CH3 NH(CH3)2 N(CH3)3 no basic character 4.74 3.36 3.29 4.28

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