[Sis290025]

Acids donate protons to water according to the general equation:

HA (aq) + H20 (l) <-> H30+ (aq) + A- (aq)

Consider the following acids and their equilibrium constants for reaction with water at 25C. If all the acids have the same initial concentration, which is the strongest acid (i.e. which donates the most protons to water)?

  a. HBrO, Kc = 2.0 x 10-9    
  b. HNO2, Kc = 4.5 x 10-4    
  c. HF, Kc = 3.5 x 10-4    
  d. HIO3, Kc = 1.7 x 10-1    


I am unsure what to do here, but, after complying equations of each in reference to the given general equation and forming the ratio of concentrations for each K_c, the higher the K_c indicates a higher proton number??? So is it HIO3??

Please explain. Thanks.

[Borek]

So is it HIO3??

Yes. The stronger the acid, the higher dissociation constant (and these K_c values are nothing else but K_a - acid dissociation constants - see acid base equilibrium and Bronsted-Lowry theory). HIO₃ has the highest dissociation constant of these four acids, thus it is the strongest.