# why HI isn't fully miscible with cold water when HF is?

HF is more soluble in water than HI , due to greater hydrogen bonding in HF , accepted but, on the other hand HF is a very weak acid so it's dissociation will be meagre when compared to HI's dissociation , so why is HF and not HI more soluble , am I misinterpreting the concept of solubility ?

• If you know what solubility is, I wonder how you'd suppose to misinterpret it. Also your assumptions about HF are wrong chemistry.stackexchange.com/questions/34818/… – Mithoron Jan 16 at 16:51
• I still could not understand , what I was able to gather from that link is , HF does dissociate but due to high electronegativity diff. thr H+ is not freed resulting in low acid strength , am I right? – Nutan Prakash Jan 16 at 18:37
• This is not off-topic, the author gives a very clear attempt to understand the underlying principles. – A.K. Jan 16 at 19:13
• @NutanPrakash Pretty much this. BTW your question may be better worded as why HI isn't fully miscible with cold water when HF is. – Mithoron Jan 16 at 19:27

Hydrogen iodide is a gas at room temperature. It's boiling point is $$-35\ ^\circ\text{C}$$. Just because it is not miscible does not mean that it is not highly soluble. The solubility of HI in water is 245 g per 100 mL. In other words, a saturated solution has more HI by mass than water. HI is a strong acid, and the solubility of the gas is due to the nearly complete ionization of HI. Since HI is a gas, I presume that the solubility limit occurs when the vapor pressure of HI above the solution is high enough that vaporization begins to compete with ionization.