Do science chemicals last well once opened?

[happypamama]

I'm putting together my list of supplies for science (biology) next year, and I'm sure there will be chemicals and such where I need a small portion but not the whole thing.  Our local homeschool store has said that they have a bunch of science chemicals.  So I'm wondering if I could buy some partially-used items from there and still have them be good.  Or, if I just buy them from Home Science Tools or somewhere, use them, and close them up well and store them appropriately, will they still be good for my next kid to use in three years, or for someone else's kid to use in a year?  Are there any things that deteriorate quickly once opened even once, such that I should always plan to buy new?

 

Thanks -- I'm in the process of deciding which labs we will do, and part of the deciding factor is going to be cost of supplies.  I'm unlikely to do a lab where I have to use a tiny bit of an expensive item that has a very limited shelf life, for instance.

[Arcadia]

Chemicals that come in brown airtight bottles or containers, and stored in a shady part of the house last well. Chemicals like Iodine solution and Benedict solution last well. Definately will last for more than a year. Not sure about three years.

 

Water absorbing chemicals like silica gel don't last well if your house is humid.

[Arcadia]

Below link has the most comprehensive list I could find so far for shelf life of common lab chemicals

 

http://www.lamotte.com/en/support/resources/reagent-list

[Reefgazer]

Depends on the chemical.  Most will be fine, others in solution will precipitate out, and hygroscopic ones will get hard (like brown sugar) if not properly stored (and most aren't properly stored).  I would avoid used chemicals because you don't know if the person stored them properly, or more importantly, if they were cross-contaminated with another chemical because of poor technique; that will really spoil your day and can potentially ruin an experiment.

[Mom22ns]

I kept all the chemicals I used between kids (and still have left overs). There were only one or two things that moisture had destroyed. Everything else still looked right and reacted as expected. Replacing just a few, and adding a few because we used different programs, was still much cheaper than buying a kit each year.