32% HCl Solution Heat of Fusion 1

[shahyar]

Does anybody know (Latent) heat of fusion (Freezing) of solution of 32% (or 33%) hydrochloric acid? (In atmospheric pressure)?
I would apprecite if I know your reference too.

Thanks

 

[m777182]

In the Handbook of chemistry and physics, The Chemical Rubber co, 52nd edition I found the melting point for HCl = -114,3degC and heat of fusion =476 cal/gmol(=13 cal/g).It does not say that it is 33w% but I think that any other value would be marked with a comment.
m777182

 

[kenvlach]

The data above is for pure HCl (not an aqueous solution).

The CRC Handbook of chemistry and physics, 79th edition, pages 8-65 to 8-66, 'Aqueous Solutions, Concentrative Properties,' gives freezing point depressions for solutions up to 12.0 wt% HCl at which the freezing point = -20.51^oC.

Perry's Chemical Engineers' Handbook, 7th Edn., page 2-15 gives these melting points:
HCl [100 wt%] -111^oC
HCl^.2H₂O [50.3 wt%] 0^oC
HCl(aq.,45.2wt%) -15.35^oC
HCl^.3H₂O [40.3 wt%] -24.4^oC
HCl(aq.,12.0wt%) -20.51^oC [from CRC Handbook]

At 32 wt% HCl, probably have solid + liquid (+ vapor) phases rather than a single melting point. Search for an HCl-H₂O phase diagram.
Calculated and experimental vapor-liquid equilibria in the HCl–H2O system are given in Figure 1 at

http://support.olisystems.com/ApplicationBriefs/MSE-Overview.PDF

This figure suggests a possible eutectic point near 0.17 mole fraction HCl. Note: 32 wt% HCl = 0.1886 mole fraction, so maybe have a freezing range (solidus & liquidus).

 

[shahyar]

Thank you guys, specially Kevlach.
Actually I couldn't find any data on "Heat of Fusion" for aqueous HCl too.

 

[kenvlach]

Probably, the value at this point has never been measured since this composition doesn't freeze (or melt) congruently; but rather, it goes through a 2-phase region, liquid + solid.

One approach: Find the H₂O phase diagram & a CRC Handbook with table I mentioned above, extrapolate a liquidus curve to 32 wt% HCl (x_HCl = 0.1886). Then find a good physical chemistry book and look up 'freezing point depression.'
For your solution, the molality m_HCl = 12.9. Water has a freezing point depression factor
k_f = 1.86 ^oK/1000 g,
so we can estimate the freezing point depression for ideal solution behavior as
[Δ]T = k_f x m_HCl
= 1.86 x 12.906
= 24.0 K
so the solution's estimated freezing point (for ideal behavior) = -24.0^oC (249.15 K). Compare this to the actual freezing point depression of the phase diagram, extrapolated as necessary, to determine the non-ideal heat of solution (mixing) [recall that [Δ]H_mix = 0 for ideal solutions]. Unfortunately, you have to model the solution behavior for both liquid and solid solutions.

So, to cut our work short, use the crude approximation
[Δ]H_fusion ~ (1- x_HCl) x [Δ]H_{fusion, H2O} + x_HCl x [Δ]H_{fusion, HCl}

[Δ]H_{fusion, 32 wt% HCl} ~ 0.8114 x 6.01 + 0.1886 x 2.0 kJ/mole
[Δ]H_{fusion, 32 wt% HCl} ~ 5.25 kJ/mole