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AP Chemistry Unit 10 – Acids and Bases

AP Chemistry Unit 10 – Acids and Bases. Lesson 2 – Bronsted-Lowry Acids and Bases Book Section: 16.2. H + is a Proton. The strength of an acid is determined on how much H + dissociates when the acid dissolves in water.

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AP Chemistry Unit 10 – Acids and Bases

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  1. AP ChemistryUnit 10 – Acids and Bases Lesson 2 – Bronsted-Lowry Acids and Bases Book Section: 16.2

  2. H+ is a Proton • The strength of an acid is determined on how much H+dissociates when the acid dissolves in water. • The ion, H+, is just a proton – so we can classify acids based on their “protonation” • A monoprotic acid has one acidic hydrogen, like HNO3 • A diprotic acid has two: H2SO4 • A triprotic acid has three: H3PO4

  3. The Hydronium Ion • When H2O interacts with free hydrogen ions, the hydronium ion, H3O+, is created. • The acidity level of a solution is determined by the concentration of hydronium.

  4. Bronsted-Lowry Acids and Bases • Rather than define an acid via presence of H+ and OH-, the Danish Johannes Bronsted and the English Thomas Lowry made a more general definition for acids and bases. • Acids are proton donors (donate H+) • Bases are proton acceptors (receive H+)

  5. Examples of Bronsted-Lowry Acids/Bases • HCl + H2O  H3O+ + Cl- • HCl + NH3  NH4+ + Cl- • NH3 + H2O  NH4+ + OH- • In each pair – which is the acid, which is the base?

  6. Conjugate Acid-Base Pairs • In an acid-base neutralization: • For every acid, there is a conjugate base. • For every base, there is a conjugate acid. • The conjugate acid is the acid for the reverse reaction, and comes from the original base. • The conjugate base is the base for the reverse reaction, and comes from the original acid.

  7. Conjugate Acid-Base Pairs • HNO2 + H2O  NO2- + H3O+ • NH3 + H2O  NH4+ + OH- • Identify the acid, base, conjugate acid, and conjugate base.

  8. Conjugate Acid-Base Pairs and Strength • A strong acid completely transfers (dissociates) its protons to water. (Ex: HNO3) • A weak acid partially dissociates in water, and exists in both a dissociated phase and a non-dissociated phase. (Ex: HNO2) • A non-acid has hydrogen but does not have acidic properties (Ex: CH4)

  9. Conjugate Acid-Base Pairs and Strength • A strong acid has a weak conjugate base. • A strong base has a weak conjugate acid. • A weak acid has a strong(er) conjugate base • A weak base has a strong(er) conjugate acid.

  10. Question • HSO4- + CO32-  SO42- + HCO3- • Which direction is favored, given acid-base strengths? (Figure 16.4 in your book)

  11. Question • HSO4- + CO32-  SO42- + HCO3- • Which direction is favored, given acid-base strengths? (Figure 16.4 in your book) • Equilibrium favors transfer of the proton from the stronger acid to the stronger base to form weaker acids and bases.

  12. HW: 16.15, 16.16, 16.18, 16.20, 16.22 • This week: • Thursday: Equilibrium Exam • Friday: Kw (16.3), Problem Set 8 Due

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