7
$\begingroup$

Some time ago, I was making a $\ce{NaOH}$ solution. The solution I had made was much too concentrated, and the heat released in the dissolution of the ions caused the water to begin steaming. Inadvertently, I inhaled some of this steam, and instantly my nose began to sting, but only for an instant. I can only assume I had inhaled some $\ce{NaOH}$, but how is this possible? How can ions be present in this steam, yet the process of distillation produces steam without ions?

$\endgroup$
9
$\begingroup$

When a liquid is evaporating or even boiling, minute drops of the liquid are formed by the mechanical disintegration of the surface of the liquid (bubble bursting, splashing or foaming). Some drops are carried away from the heated liquid by the steam (by convective and vapour flow).

The concentration of non-volatile dissolved matter in the entrained drops approximately corresponds to the concentration in the bulk liquid. Therefore, if the bulk liquid contains $\ce{NaOH}$, the entrained drops also contain $\ce{NaOH}$.

A quantitative parameter that describes this transport is the airborne release fraction (ARF). The ARF increases with temperature of the liquid and air velocity above the liquid. Measured values for liquids that are evaporating but not boiling range from $< 10^{-8}$ to $3\times10^{-5}$ (Mishima, J., L.C. Schwendiman and C.A. Radasch. November 1968. Plutonium Release Studies IV. Fractional Release From Heating Plutonium Nitrate Solutions in Flowing Air Stream, BNWL-931, Pacific Northwest Laboratory).

In principle, distillation and similar technical processes have the same problem. That is one reason why distillation shows only a limited decontamination factor (DF) even for non-volatile dissolved matter.

$\endgroup$

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.