question about storing opened 99% iso alcohol

While I only need a bit of 99% iso alcohol here and there, I was thinking of purchasing the larger bottle of it because for $ 2 more you can get nearly eight times as much [MG Chemicals' 99.9% iso alcohol $ 12.95 for 945ml versus $ 10.39 for 125ml at amazon.com]

Besides a possible risk of losing product due to evaporation over time, is there any other disadvantage if it could take me a year to year and a half to use the 945ml bottle after opening it ? Is there much risk of the 99.9% alcohol becoming appreciably diluted through absorbing moisture from the indoors atmosphere over a long period of time ?

I still have an empty 125ml bottle that I could refill with the 945ml so that I would have to uncap the 945ml less often. Also, would it help seal in the alcohol if I were to put a square of tinfoil or Saran Wrap press-and-seal wrap underneath the 945ml bottle cap ?

I have been googling around and can't find any figures for how long it takes to absorb moisture from the atmosphere

But I'd guess you'd be pretty safe to decant it in to smaller 'for use' bottles and keep the main stock fully sealed.

If you were that worried I am sure you could buy a long term storage bottle with a better cap, but I am sure the container it comes in must be good enough for the job

What are you using it to clean? Electrical contacts etc?
If so am pretty sure you are not going to notice the difference between 99% and whatever small amount of moisture it takes in from the atmosphere.
Most store bought isoprop I have seen is often only 70% anyway.

And as for loss via evaporation, well, a good quality glass storage vessel or its original transport container well sealed with no additional layers between the cap and bottle top should be all you need.

I did have a table somewhere about ethyl alcohol and its water absorbing properties and speed of absorption in relation to RH and use in vehicles as fuel , so J guess if you searched enough you could dig up similar in relation to isoprop, but I doubt it is worth worrying about.




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Thank you for your guidance and thoroughly addressing my concerns

My forseeable use for it is cleaning flashlights and, since it's rated as safe on plastic, cleaning the plastic housing and plastic interior of contaminated electronic gadgets. I also thought I could use it to clean some dusty/dirty indoor door hinges prior to lubricating them.

For your use, the amount of water that us going to be absorbed from the atmosphere is not going to make any noticeable difference to your usage.
I have a container here, bought off the shelf that is 70%. I doubt the 99% would dilute via moisture adsorption to anything like that amount.

I'd just go ahead buy the big one and decant into smaller containers, if for no better reason than to prevent wastage due to accidental spillage or contamination.


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Two things...

1) I buy my 99% from the local Safeway grocery store ( AKA Vons, Albertsons) in 16 ounce bottles. It's around 2 bucks a bottle here in California.

2) The amount of water that will be absorbed from the air will depend on the humidity at the time that you open the bottle and how much air actually gets in the bottle. I poke a small hole in the aluminum foil seal and squirt the alcohol out. I suspect that the total air infiltration is the same as the amount that I squirt out, so over the course of a year there is only 500 ml of air in the bottle.

3) Acrylics will craze and crack when cleaned with alcohol.


Dan

I have some that is several years old.... Still works fine. Keep the lid on it and keep it away from heat. You won't have any problems....