3.Acid Strength A strong acid is one that is completely ionized in water. A weak acid is one that ionizes in water to the extent of less than 100%. Acid strength is measured by Ka or pKa
3. Acid Strength A stron g acid is one that is completely ionized in water. A weak acid is one that ionizes in water to the extent of less than 100%. Acid strength is measured by Ka or pKa
Equilibrium constant for proton transfer H-Br: [HO][Br广] K= [HBr] [H][B广] [HBr] pK a =-log Ka
Equilibrium constant for proton transfer [H 3 O +][Br– ] [HBr] K = K a = [H +][Br– ] [HBr] H Br H H . .O H .. .. . . + p K a = – log Ka O H H . . . . Br – . . . . .. .. + +
Strength of Some Bronsted Acids Acid pKa Conj.Base HI ~1010 -10 HBr ~109 -9 Br HCI ≈107 -7 cr H2S04 1.6x105 -4.8 HSO4 H3O* 55.5 -1.7 H20 strong acids are stronger than hydronium ion
Strength of Some Brønsted Acids strong acids are stronger than hydronium ion Acid Ka p Ka Conj. B a s e HI ~1 010 –1 0 I – HB r ~ 1 0 9 –9 B r – HCl ~1 0 7 –7 Cl – H 2SO 4 1.6 x 1 0 5 –4.8 HSO 4 – H 3 O + 55.5 –1.7 H 2 O
Strength of Some Bronsted Acids 十十 Acid K pKa Conj.Base HsO* 55.5 -1.7 H20 HF 3.5x104 3.5 F CH3CO2H 1.8x105 4.6 CH3CO2 NH4* 5.6x10-10 9.2 NH3 H20 1.8x10-16 15.7 HO weak acids are weaker than hydronium ion
Strength of Some Strength of Some Brønsted Acids Acid Ka p Ka Conj. B ase H 3 O + 5 5.5 – 1.7 H 2 O H F 3.5 x 1 0 – 4 3. 5 F – CH 3 C O 2 H 1.8 x 1 0 – 5 4. 6 CH 3 C O 2 – NH 4 + 5.6 x 1 0 –10 9. 2 NH 3 H 2 O 1.8 x 1 0 –16 1 5.7 H O – weak acids are weaker than weak acids are weaker than hydronium hydronium ion
Strength of Some Bronsted Acids Acid K pKa Conj.Base H2O 1.8x1016 15.7 HO CHsOH ~1016 ~16 CH3O CH3CH2OH ~1016 ~16 CH3CH2O7 (CH3)2CHOH ~1017 ~17 (CH3)2CHO7 (CH3)3COH ~1018 18 (CH3)3CO alcohols resemble water in acidity;their conjugatebases are comparable to hydroxide ion in basicity
Strength of Some Strength of Some Brønsted Acids Acid Ka p Ka Conj. B ase H 2 O 1.8 x 1 0 -16 1 5.7 H O – CH 3 O H ~ 1 0 -16 ~ 1 6 CH 3 O – CH 3CH 2 O H ~ 1 0 -16 ~ 1 6 CH 3CH 2 O – (CH 3 ) 2CH O H ~ 1 0 -17 ~ 1 7 (CH 3 ) 2CH O – (CH 3 ) 3 C O H ~ 1 0 -18 ~ 1 8 (CH 3 ) 3 C O – alcohols alcohols resemble water in acidity;their resemble water in acidity;their conjugatebases conjugatebases are comparable to hydroxide ion in comparable to hydroxide ion in basicity basicity