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Strong and Weak A cids and Bases

Strong and Weak A cids and Bases. Topic 8.3. A cids. w hen a STRONG acid dissolves- all, or nearly all, of the acid molecules react to produce H + or H 3 O + ions (reaction goes to completion) have a very high K c value HA  H + ( aq ) + A - ( aq ) 0% ~100%

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Strong and Weak A cids and Bases

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  1. Strong and Weak Acids and Bases Topic 8.3

  2. Acids • when a STRONG acid dissolves- all, or nearly all, of the acid molecules react to produce H+or H3O+ ions (reaction goes to completion) • have a very high Kc value • HA H+(aq) + A-(aq) 0% ~100% • HA + H2O(l)  H3O+(aq) + A-(aq) 0% ~100% • equilibrium is so far to the right for strong acids that we use a yields symbol () instead of an equilibrium symbol (⇌) Initial amount of HA HA H+ A- At Equilibrium

  3. common strong acids (need to know) • hydrochloric acid: • HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq) • nitric acid: • HNO3(l) + H2O(l)  H3O+(aq) + NO3-(aq) • sulfuric acid: • H2SO4(l) + H2O(l)  H3O+(aq) + HSO4-(aq)

  4. when a WEAK acid dissolves, very few acid molecules react to produce H+ ions (equilibrium lies to the left) • have a very lowKc value • HA ⇌H+(aq) + A-(aq) 99% ~1% • HA + H2O(l) ⇌H3O+(aq) + A-(aq) 99% ~1% Initial amount of HA HA At Equilibrium HA H+ A-

  5. common weak acids (know these) • carboxylic acids (contains one or more carboxylgroups, COOH): • acetic acid • CH3COOH(l) + H2O(l) ⇌ CH3COO-(aq) + H3O+ • carbonic acid: (CO2 in water) • CO2(aq) + H2O(l) ⇌ HCO3-(aq) + H+(aq)

  6. Characteristics of strong vs. weak acids • equal [conc] of strong and weak acids can be easily distinguished: • acid strength does not change when a solution is diluted, only the concentration (molarity) does • do not confuse strong and weak, with dilute and concentrated • concentrated = high molarity (M) • 0.1 M HCl (strong) vs 0.1 M CH3COOH (weak) • same concentration, different strength

  7. strong acids • have more H+ ions, hence lower pH • higher conductivity • react more vigorously with metals, metal oxides, metal carbonates and bicarbonates • have a more (-)∆H of neutralization (more heat) • dangerous • weak acids • opposite of strong acids

  8. Bases • when a STRONG base dissolves, nearly all the base molecules react to produce hydroxide (OH-) ions solution • have a very high Kc value • BOH + (aq)  OH-(aq) + B+(aq) 0% ~100% • equilibrium is so far to the right for strong bases that we use a yields symbol () instead of an equilibrium symbol (⇌)

  9. common strong bases • all group I hydroxides and barium hydroxide • NaOH(s) + (aq)  Na+(aq) + OH-(aq) • KOH(s) + (aq)  K+(aq) + OH-(aq) • Ba(OH)2(aq) + (aq)  Ba2+(aq) + 2OH-(aq)

  10. when a WEAK base dissolves, very few base molecules react to produce OH- ions • have a very lowKc value • BOH + (aq) ⇌OH-(aq) + B+(aq) 99% ~1%

  11. common weak bases • ammonia • NH3(g) + (aq) ⇌ NH4+(aq) + OH-(aq) • amines (contain NH1,2, or 3): • ethylamine • C2N5NH2(g) + H2O(l) ⇌ C2H5NH3+(aq) + OH-(aq)

  12. strong vs. weak base characteristics • strong bases • has more OH- ions, hence higher pH • higher conductivity • have a more (-)∆H of neutralization (more heat) • dangerous • weak bases • opposite of strong bases

  13. http://phet.colorado.edu/en/simulation/acid-base-solutions

  14. Using experimental data to determine acids and bases • Given the following are 0.1 M solutions, determine whether an acid or base, and strength • ph of 1: strong acid • poor conductor with pH of 6: weak acid • fast reaction with magnesium: strong acid • [H+] = 10 -10M: weak base • [H+] = 10 -4M: weak acid • neutralized 0.1M HCl quickly: strong base • good conductor with pH of 13: strong base • slow reaction with calcium: weak acid • has a high -ΔH when reacting with a base: strong acid

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