Why is the alcohol in the drug store labeled 91% when it is apparently 100%?

The alcohols form an azeotrope with water (look up azeotrope) making it really difficult to get to 100%. By normal destillation you'll get to 70%.

Really concentrated ethanol (96%) is usually made by azeotropic destillation with toluene, to drive the water into a second azeotrope with toluene instead of alcohol. After doing this it still contains around 4% water and attracts moisture from the air.

Absolute ethanol is usually obtained by destillation over metallic sodium or P2O5. The same story goes for isopropyl alcohol, but here the azeotrope is at 91% instead of 70%.

The process of "salting out" makes ethanol less soluable in water (but not unsoluable) because the water gets saturated with salt. However, you probably still got two azeotropic mixtures. The water layer probably still contains a small amount of ethanol and the ethanol layer still a small amount of water.

You can test wether it's dry (and thus 100%) by adding anhydrous sodium sulfate. If it's cloudy when you shake it, it's dry, but when it sits at the bottom as a big clump it's wet. Another good indicator is benzophenone with elemental sodium which is strongly coloured as diphenylketyl when your alcohol is dry.

No one ever says "i need to be a junkie once I grow up" but when your best 16 and are using such as you describe, there is only one alternative, it's going to be hard, find something else to do. Spend your money on some thing productive, discontinue hangin around different users and don't go to parties, buy a paintball gun and to find some other paintballer within the field and the longer you don't are living the customers existence the simpler it is going to be to now not believe about it all the time and quit SMOKING CIGS. Thats gotta be the hardest thing to do, but your young and will have to be a little bit less complicated, the opposite alternative is to discontinue utilizing, but still go to events and cling with the equal friends, nevertheless it will not WORK, it could appear to work for a month or two however then you'll wish to have that prime feeling "just another time and that'll be it" however bear in mind you didn't emerge as a junkie over night and you're going to turn out to be the identical way you are now or worse

you're assuming it took out all the water of the 70% it may of in fact just took out enough to make it 91% or less. It took out some water, but how much? Maybe it only gave you 80%, did you measure and see what the water content was after you added salt? It just means you need a more efficient drying agent which would cost you more than just buying it from the store in the first place

Probably for the same reason distilled ethyl alcohol is really 95% alcohol. It binds water in a way that makes that last bit difficult to separate by simple methods like distillation.