Sulfur dioxide ionizes in water by non-standard reaction SO_2 + H_20 H+ + HSO3- (without formation of H_2SO_3 molecules). The constant of this reaction is rather large (~10^-2), so ionization will definitely be significant. Indeed, the SO_2 in water solution is an acid with strength close to oxalic acid and even to HSO_4- ions.

As concerns to HCN, it is very weak acid (K ~ 10^-10, if I am mistaken correctly), which is about 3 orders less that that of H_2S (K(1) ~ 10^-7)

With best regards,

Victor N. Kuznetsov

@Victor Nickolayevich Kuznetsov

Thanks a lot for your useful answer.

You need to check their pKa

@ Navid Saeidi: Thanks a lot for your answer. Does the high value of pKa mean that the ionization is significant?

Protonation and association of your target compounds in solution depend on both the pKa of your target compounds and pH of your solution. If the pH is higher than the pKa, then the compound will be associated and vise versa. To my knowledge when the pKa of the compound is equal to the pH of solution, then there would be an equilibrium and niether association nor protonation. For instance:

A pKa of 2 for substance “X” means that at a pH of 2, X is at its equilibrium point. If the pH falls to 1, then X will accept a proton. If the pH rises to 3, then X will give up a proton.

Hope it works my friend Shahin.

@Navid Saeidi: Thanks a lot Navid.