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Acids and Bases

Acids and Bases. Chapter 8. Equilibrium and Acids & Bases. So far, we have looked at equilibrium of general chemical systems: We learned about the equilibrium constant K, reversibility, factors that affect or shift equilibrium, using ICE charts and calculating K eq

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Acids and Bases

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  1. Acids and Bases Chapter 8

  2. Equilibrium and Acids & Bases • So far, we have looked at equilibrium of general chemical systems: • We learned about the equilibrium constant K, reversibility, factors that affect or shift equilibrium, using ICE charts and calculating Keq • Now we are going to look at equilibrium, applying the concept to Acids & Bases • Calculating Ka and Kb • Before we begin, we better review Acids & Bases from Grade 11!!

  3. Acids & Bases There are many substances that change the hydrogen ion concentration [H+] when dissolved in water. • Binary acids (HF, HCl, HBr, HI, H2S, etc) • Oxyacids (HNO3, H2SO4, HClO4, etc) • Organic acids (acetic acid, methanoic acid, etc) • Hydroxy bases (NaOH, Ca(OH)2, KOH, etc) • Amine bases (methylamine, dimethylamine, etc.)

  4. Definition of acids & bases • Empirical definition – defined based on observed properties in experimental conditions.

  5. Empirical definition of an acid • Turns litmus red • Reacts with base metals to produce H2 gas • Reacts with carbonates to produce CO2 gas • Conducts electricity • Tastes sour • Feels dry or rough • Is colourless in phenolphthalein • Turns bromothymol blue to a yellow

  6. Empirical definition of a base • Turns litmus blue • Does not react with metals or carbonates • Conducts electricity • Tastes bitter • Feels slippery • Turns pink in phenolphthalein • Turns blue in bromothymol blue

  7. Common Properties of Acids & Bases

  8. Acid-Base Theories • ÅrrheniusTheory of acids & bases • Founded on the production of H+ or OH- when a substance is dissolved in water • An acid ionizes in water to produce hydrogen ions (H+) or hydronium ions (H3O+). HBr(aq) + H2O  H3O+(aq)+ Br-(aq) H2O + H +(aq)  H3O+(aq)

  9. Acid-Base Theories Acid-Base Theories • ÅrrheniusTheory of acids & bases cont.. • A base ionizes in water to produce hydroxide ions (OH-). KOH(s)+ H2O(l) K+(aq)+ OH-(aq)

  10. Acid-Base Theories Acid-Base Theories • ÅrrheniusTheory cont.. • Adequately explains the behaviour and properties of most acids and bases, but • Limitations: • does not explain acid-base reactions without water (i.e. gas) • fails to explain how compounds such as ammonia (NH3(aq)) can behave as bases without any hydroxide ions (OH-) in the substance. NH3(g)+ H2O(l) NH4+(aq)+ OH-(aq)

  11. Brønsted-Lowry Theory • The second theory of acids/bases uses the transfer of protons (H+). • Brønsted-Lowry Acid • A substance that donates protons. • Brønsted-Lowry Base • A substance that accepts protons.

  12. Brønsted-Lowry Theory Brønsted-Lowry Theory H2O(l) + HCl(aq)  H3O+(aq)+ Cl-(aq) Base Acid Conjugate Conjugate acid base HCl donates the H+ – Acid H2O will accept the H+ – Base H3O+ can donate the H+ it received – Conjugate acid Cl- can accept available H+ ions – Conjugate base

  13. Acid-Base Equilibria Acid-BaseEquilibria • In the Brønsted-Lowry theory of acids & bases the concept of equilibrium is implied. • The acid-base system appears reversible. • Acids donate hydronium ionsin the forward reaction while the conjugate acids donate hydronium ions in the reverse reaction.

  14. Brønsted-Lowry equilibrium H+ H+ H2O(l)+ HCl(aq) H3O+(aq)+ Cl-(aq) BaseAcidConjugateConjugate acidbase Forward reaction proton donator – Acid Forward reaction proton acceptor – Base Reverse reaction proton donator – Conjugate acid Reverse reaction proton acceptor – Conjugate base

  15. Brønsted-Lowry equilibrium Brønsted-Lowry equilibrium H2O(l)+ HCl(aq) H3O+(aq)+ Cl-(aq) BaseAcidConjugateConjugate acidbase • Competition for protons occurs between the base and the conjugate base. • The state of the equilibrium will be determined by the capacity for the acid to produce protons in comparison with the conjugate acid’s capacity to do the same.

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