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Acids and Bases

Acids and Bases. Properties and definitions http://www.youtube.com/watch?v=ZII7upCDIy0&feature=related. Observable Properties. Sour . Bitter . Yes . Ie . forms electrolytes. Yes . Ie . forms electrolytes. No characteristic feel . Slippery . Turn blue litmus red . Turn red litmus blue .

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Acids and Bases

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  1. Acids and Bases Properties and definitions http://www.youtube.com/watch?v=ZII7upCDIy0&feature=related

  2. Observable Properties Sour Bitter Yes Ie. forms electrolytes Yes Ie. forms electrolytes No characteristic feel Slippery Turn blue litmus red Turn red litmus blue Produce CO2 Don’t react Produce H2 Don’t react

  3. Acid or Base? Citric Acid Sodium Hydrogen Carbonate Lactic Acid Acetic Acid Ammonia NaOH Carbonic Acid 3-methyl-2-hexanoic acid

  4. Arrhenius Acids and Bases • Studied the dissociation of a number of acids and bases in water: HBr(aq) H+(aq) + Br-(aq) H2SO4 (aq) H+(aq) + HSO4-(aq) HCl(aq) H+(aq) + Cl-(aq) NaOH(aq) Na+(aq) + OH-(aq) KOH(aq) K+(aq) + OH-(aq) Ba(OH)2 (aq) Ba+(aq) + 2OH-(aq) • Arrhenius Acid-Base Theory (1887): • An acid is a substance that dissociates in water to produce one or more hydrogen ions, H+ • A base is a substance that dissociates in water to produce one or more hydroxide ions, OH- Write this down!

  5. Arrhenius Limitations • When it’s good: • Looking at just the ions when an acid/base dissociates in H2O HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) H+(aq) + OH- (aq) H2O(l) • When it’s bad: • When you want to use H2O in the reaction equation HCl(aq) + H2O(l) H+(aq) + Cl-(aq) + H2O(l) • Does H2O really remain H2O? • When it’s ugly: • What about bases that don’t fit the definition? NH3(g) + H2O(l) NH4+(aq) + OH-(aq)

  6. Arrhenius Limitations • “Modern” Arrhenius theory acknowledges the role of H2O (and production of H3O+) • However, it still cannot explain the basic properties of ammonia (for example) • Also, it assumes all acid-base reactions take place in a single solvent • Cannot always predict if a compound is acidic or basic • Example, HPO42-

  7. What now? BrØnsted-Lowry! • 1923 two chemists working independently came up with a new theory: • The BrØnsted-Lowry Theory of Acids and Bases: • An acid is a substance from which a proton (H+ ion) can be removed • A base is a substance that can remove a proton (H+ ion) from an acid Proton Donor Proton Acceptor Write this down!

  8. BrØnsted-Lowry Acids and Bases • Like an Arrhenius acid, must contain H • So, all Arrhenius acids are also BrØnsted-Lowry acids • Any negative ion (not just OH-) can be a base • Only one requirement: a proton is transferred from one substance to another • Consider this: Lets look at HCl again:

  9. Conjugate Pairs Conjugate = “linked together” Conjugate base has one less H+ than the acid The conjugate acid has one more H+ than the base Conjugate Base Acid Base Conjugate Acid

  10. Conjugate Pairs- Try It! Hydrogen bromide gas dissolves in water at room temperature to form hydrobromic acid. Identify the conjugate acid-base pairs.

  11. Conjugate Pairs- Try It! Ammonia is a pungent gas at room temperature. It is used in fertilizers and explosives. It is also very water soluble and forms a basic solution (often used in glass cleaners). Identify the conjugate acid-base pairs in the reaction between ammonia and water.

  12. Hold Up! What’s going on with water? Substances that act as both acids and bases are said to be amphoteric Base Acid

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