help me w/thse chemistry instructions

July 25, 2010 11:43 AM

Quick chemistry question - do i need to dilute this or is it already diluted

I'm following these instructions - here

and it says to dilute two parts water to one part ammonium hydroxide

but the ammonium hydroxide i bought says this

so do i still need to dilute, what with the mention of it being 28 percent to 30 percent by weight, or does that just refer to the ammonia in it and i still need to dilute?

thanks!

posted by Salvatorparadise to Science & Nature (12 answers total)

Yes. 200 mL of water and 100mL of Ammonium Hydroxide (for example)

Concentrated Ammonium Hydroxide is ~28 percent and you're being asked to dilute that further. It's a bit confusing because you typically think of concentrated as 100%, but in chemistry it's often not.

I'm a Chemistry teacher (but not yours, so your mileage may vary).
posted by jz at 11:51 AM on July 25, 2010

I don't know the answer to your question, but I wanted to warn you that ammonium hydroxide is about as caustic as sodium hydroxide AKA lye. Be careful; you can get very badly burned. Wear rubber gloves, OK?
posted by Chocolate Pickle at 11:53 AM on July 25, 2010

Your "this" link is kinda borked for me. Try this.

And FWIW, yeah it sounds to me like you should go ahead and add the two parts water to the ammonium hydroxide you bought.
posted by trip and a half at 11:55 AM on July 25, 2010

Yes, seconding Chocolate Pickle. I only use Ammonium Hydroxide in a fume hood at school. The vapors are caustic and will burn your eyes, nose, throat.

Goggles are a must. Ventilation is key. A mask would be helpful
posted by jz at 11:56 AM on July 25, 2010

Response by poster: i thought so, thanks everyone

and i plan on wearing rubber gloves, safety goggles etc.
posted by Salvatorparadise at 12:10 PM on July 25, 2010

Yes, you need to dilute it. What the instructions (first link) are saying is that concentrated ammonium hydroxide is about 28% NH4OH (by weight, I assume, and the rest is water), and you need to dilute that further. Two parts water plus 1 part NH4OH gives three parts total, so you've diluted your starting solution to one third its original concentration, or 28 / 3 = 9.3%.

Your second link is borked for me, but assuming you purchased concentrated ( = 28%) NH4OH, dilute it per the instructions. If it's some other concentration, figure out how to get it down to 9%.
posted by Quietgal at 12:16 PM on July 25, 2010

Worth noting is the grade. The bottle pictured says ACS Reagent Grade. This indicates that it is very high purity, generally the highest you'll get before cost becomes absurd. You will need to dilute it, but make sure you know whether it's by volume or weight.

Next step down is USP grade, this is usually enough for home chemistry experiments. Often cheaper than reagent grade.

Below that, is technical grade. Technical grade is usually not pure enough for home chemistry work.
posted by wackyvorlon at 12:19 PM on July 25, 2010

Response by poster: that's good to know, i probably don't need that reagent's grade

thanks!
posted by Salvatorparadise at 2:31 PM on July 25, 2010

Diluting concentrated acids and bases tends to generate heat, so add this to cold water and not the other way around. If you get this on your skin, it's not going to eat to the bone in seconds or anything, so don't panic. (Nothing like panic to turn a minor mishap into a disaster.) Just go wash it off.

Eye damage is the big danger here, followed by having your throat and lungs roughed up by the vapors. It would be a good idea to do the initial dilution outside or somewhere with very good ventilation. The diluted solution is still going to be pretty strong, but the reagent grade stuff will be like getting hit in the face with a board. If you work with it chilled that will keep the more ammonia in your solution and less in your air, but it might interfere with what you're doing.
posted by Kid Charlemagne at 4:34 PM on July 25, 2010

Response by poster: oh yeah, i got the odor for sure

-is there a type of respirator that is easy to find that I can use to block this?
posted by Salvatorparadise at 5:21 PM on July 25, 2010

Good ventilation is key. I'm not sure what cartridge you need to deal with ammonium hydroxide. See if you can do this outside.
posted by wackyvorlon at 6:38 PM on July 25, 2010

I just did some digging, and found this. It's a cartridge suitable for use with ammonium hydroxide. You'd need two of these with a respirator.
posted by wackyvorlon at 8:13 PM on July 25, 2010