3
$\begingroup$

If in a reaction mixture HCl is given in liquid phase, will it behave as an acid ?

I know that an aqueous solution of HCl is acidic but am confused about the liquid phase.

$\endgroup$
4
$\begingroup$

It would act as an acid if there were even slightly basic atoms available to protonate. Pure liquid HCl probably would probably have a pretty high $\text{p} (\ce{H2Cl^+})$, though, due to the very low basicity of the chloride ion. In other words, it would have a very low autoionization constant, similar or less than that of $\ce{H2SO4}$ (which has a higher pKa pure than it does in water), based on their similar aqueous pKa values.

I say "less than" because stabilizing ions would be harder due to the smaller size and higher concentration of charge of the $\ce{H2Cl^+}$ and $\ce{Cl^-}$ ions relative to the more diffuse $\ce{H3SO4^+}$ and $\ce{HSO4^-}$ ions.

| improve this answer | |
$\endgroup$
  • 1
    $\begingroup$ In fact, autoionization constant of $\ce{H2SO4}$ is not that low; it is way higher than that of water. Not sure about liquid $\ce{HCl}$, though. $\endgroup$ – Ivan Neretin Mar 27 '16 at 7:01
  • 1
    $\begingroup$ @IvanNeretin Indeed, $\ce{H2SO4}$ is has a much higher autoionization constant than water, but as far as mineral acids go, I think it's fairly low. Interestingly, sulfuric acid autoionizes to water and hydrogen pyrosulfate. It's autoionization constant is $7x10^-5$. Nitric acid, however, has an autoionization constant of $2x10^-2$. I haven't yet found one for $\ce{HCl}$, and I'm still looking, but I believe it would be much less than either of these. $\endgroup$ – SendersReagent Mar 27 '16 at 8:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.