by the way, I am not a student (although this may sound like a homework problem)...the reason I am asking is because a sample of what we believe is 5% IPA was sent out for flashpoint determination and the results were 54 and 56 degrees fahrenheit. This does not sound right.
Guess I always thought flashpoint was something determined by testing. ASTM have published methods for determining flashpoint by test. I'm sure there are other sources but here's one link to look at
Data I have for isopropyl alcohol indicates it alone has a flash point of about 12C. I would suspect a 5vol% solution in water would be higher.
You might could find that a supplier produces such a mixture and get the info you need from their MSDS.
Now if you are interested to know if the mixture can produce an explosive atmosphere above the liquid, you could use Raoult's law and Dalton's law to determine the concentration of isopropyl alcohol in the vapor space and compare that to the lower and upper explosive limits for isopropyl alcohol (2%-13%) to see if it is in the combustible range.
Looks like you made a second post while I was composing my first and from your second post I can see your dilema, the flash point for your 5% solution appears to be identical for "pure" IPA.
I don't have detail knowledge of the test methods and that may be where the catch is. Found this link that explains a little more about the test but you may want to get a copy of the ASTM method for full details
Thanks for the info EGT01...i think at this point, I will send out the sample to a different lab as a sanity check and also go over my old chemical thermodynamics book again. This is vexing, especially if the flashpoint determination from the first lab is correct...it would require appropriate storage and shipping containment.
I think you have to consider Differences in these Physical States also, i.e for isopropyl is:
Boiling Point/Range: 82°C (180°F)
Solubility in Water: Miscible
Vapor Density(Air=1): 2.1
AND MOST LIKELY:
Evaporation Rate(N-Butyl Acetate=1): 2.83
Here is a quote from a discussion on this subject.
In response to your question regarding the flashpoint of a solution of 20% IPA, I am assuming that the IPA is either in water or fountain solution and it is by volume and not weight. In one study, a 20% concentration, the closed cup flashpoint was reported to be 87oF. Another study reported a flashpoint of 82oF. Neither of the studies reported what concentration of IPA would produce a closed cup flashpoint of 140oF. The lowest concentration tested was 5% by volume and both studies seem to agree 122.5 vs 123.8 oF. While it is not clear from your email why you are interested in this data, recognize that solutions containing less than 25% alcohol are not considered a hazardous waste due to the characteristic of ignitability (flashpoint < 140oF).
Go to one of the many activity coefficient calculators available on the web or use the Henry's constant for
IPA in water. Use this to calculate the concentration of IPA in the vapor above the liquid at various temperatures & compare to the LEL of IPA. The temperature at which the IPA vapor concentration equals the LEL is approximately the flash point.
