[schmidling]

I bought a sample kit of acid dyes for dying wool fabric.

One of the ingredients added to the dye batch is an acid.  The acid included is identified as Ammonium sulfate and the amount used is in grams.

I think most people use Citric Acid and I have lots of this stuff but don't  know how to relate it to Ammonium sulfate.

Both are powders so can I just use similar amounts or how would I compare them?

Jack

[Corribus]

You can't just weigh out the same amount because the acids have different acidities.  Citric acid (pKa ~ 3.1 for first dissociation) is a lot more acidic than the ammonium ion (pKa ~ 9.3).  There's also molecular weights to worry about.  Basically if you dissolve 1 gram of citric acid in water and 1 gram of ammonium whatever, the pH values of the solutions would probably be quite different.  It would be possible to calculate an equivalency to determine how much citric acid you would use to get the same pH, but if it's a kit, why don't you use what is included?  It's hard to say without knowing exactly what the kit is trying to accomplish, but it's also possible the ammonium sulfate is playing some other role besides changing the pH.  Therefore even if you calculated the right amount of citrate to add, it's possible the process still might not work depending on the chemistry involved.

[Montegue]

If your purpose is to dye fabric, acid is used to set the color, so that it doesn't immediately washed out. Citric Acid is organic acid. Orange and lemon contain citric acid. The acid in orange or lemon won't hurt you, but it will burn if you have open cut on your skin. Citric acid at low concentration won hurt; it's safe for dying fabric.

Ammonium sulfate is very stable. It's a form of salt crystal. Ammonium sulfate is commonly used as nitrogen fertilizer. When dissolved in water, it ionizes into ammonium and sulfate. The sulfate once in the water will combine with the hydronium in the water to form sulfuric acid. When the sulfate reacts with other substance, the ammonia will escape into the air.

I usually use half a table spoonful to mix it with a gallon of water for fertilizing my plants once a year. At a concentration like this, the sulfuric acid won't hurt you. For use at home, most people don't do chemical calculation or measure things like in lab. For practical purposes, half a spoonful per gallon of water should do for dying fabric. If the result is not satisfactory, you can try again by doubling teh concentration. Whatever you do, don't use too much. It's not good for you or the fabric. It's also bad for the environment. Doing it outside the house is better or keep your windows open while doing it.

[Borek]

The sulfate once in the water will combine with the hydronium in the water to form sulfuric acid. When the sulfate reacts with other substance, the ammonia will escape into the air.

Sorry, this is an awful combination of half truths and misunderstandings. Sulfate will not combine with hydronium in water to form sulfuric acid. If anything, in such a solution ammonium ions (NH₄⁺) behave like an acid, dissociating and lowering pH of the solution. And you need a very specific substance to release the ammonia - a strong base. Not any substance, as you seem to be suggesting.

[Montegue]

half understanding yes; half-truth no.

[Borek]

I don't think it was intentional, I am just judging the result.

[Montegue]

Both are powders so can I just use similar amounts or how would I compare them?

The answer to your question is here:
http://www.pburch.net/dyeing/FAQ/ammonium_sulfate.shtml

[vmelkon]

If you want to know if a solution of (NH4)2SO4 will be acidic or basic, you need to compare the Ka of the acidic portion to the Kb of the basic portion.
NH4+ will act as an acid. Ka = 5.6e-10
NH4 + H2O <-> NH3 + H3O+
SO4(2-) will act as a base. Kb = 8.3e-13
SO4(2-) + H2O <-> HSO4- + OH-

Ka is higher, therefore the solution should be acidic.

PS: the sulfate ion doesn't react to make (H2SO4) because the first dissociation is very very high. The second dissociation is low, 1.2e-2. There won't be any H2SO4.

[Montegue]

Thank you, vmelkon. I have learned it, but this is the first time I see the application. You have kind heart of a good teacher.