Commercial Sodium Hydroxide Solution Freezing Point
Commercial Sodium Hydroxide Solution Freezing Point
(OP)
My books indicate that a 25% solution of sodium hydroxide should have a freezing point of around -18 deg C.
However a local reputable reagent supplier tells me that their 25% solution freezes on a cold (say 0 deg C) day.
Any ideas why the difference? Stratification,impurities, book error?
I had intended to use 25% to avoid the need for heat tracing.
Cheers
Steve
However a local reputable reagent supplier tells me that their 25% solution freezes on a cold (say 0 deg C) day.
Any ideas why the difference? Stratification,impurities, book error?
I had intended to use 25% to avoid the need for heat tracing.
Cheers
Steve





RE: Commercial Sodium Hydroxide Solution Freezing Point
The CRC Handbook of Chemistry and Physics gives the lowest F.P. of -16.8oC for a 14% mass solution of NaOH. I don't have the data, however, I believe that beyond this point richer concentrations have higher F.P.
Even sodium chloride with a minimum F.P. of ~ -21oC at ~23% mass, raises its F.P. up to zero Celsius at 26.3 % mass. So, your supplier may be right after all.
RE: Commercial Sodium Hydroxide Solution Freezing Point
25% by weight has a freezing point of about -20C. However, the freezing point rapidly rises with increasing strength. At about 28% to 29%, you are up near 0C for a freezing point. That may be what your supplier is thinking about, possible variations in solution strength. I don't know if you are bringing in 25% caustic soda or if you are diluting a higher strength solution (for bulk, 50% is a common strength to save costs of shipping water).
RE: Commercial Sodium Hydroxide Solution Freezing Point
TD2K is correct....
Unless you live in interior Alaska, the 25% solution will be acceptable for use without heat tracing.
Everybody and thier brother, purchases 50% soulution and immediately dilutes to 25%
In addtion to DOW Chemical, PPG industries (and others) have guidelines for "caustic soda handling" available on the internet....
Try this one.....
http://www.oxychem.com/products/handbooks/caustic.pdf
Tell us more about you system, particularly the tankage and delivery volumes....
Cheers !!
MJC