[ehanson999]

To mix an etching solution at my company, we have instructions which say to dissolve Ammonium Bisulfate and Ammonium Bifluoride in a tank of de-ionized water. The specifications are as follows: Volume of water is about 15.6 gallons; concentration of Amm Bisulf is 16 oz/gal; concentration of Amm Bifluor is 1 oz/gal.

I know that the resulting solution is a weak acid, but I don't know specifically what kind of acid it is. FYI, my chemistry knowledge extends as far as two semesters of basic college chemistry for scientists.

Essentially, my question is: What are the products of the following reactant equation?

?H₂O(l) + ?(NH₄)₂(S₂O₈)(s) + ?(NH₄)(HF₂)(s)  ??

I don't know how to determine which atoms/ions will change positions. Any help is appreciated!

[Borek]

There is no reaction, only dissociation.

[ehanson999]

There is no reaction, only dissociation.

Ok; I think I understand what you mean. Are hydrogen ions dissociated from the Amm Bisulf and the Amm Bifluor, thereby making the solution acidic?

Is there a name for the acid that is created?

[Borek]

Are hydrogen ions dissociated from the Amm Bisulf and the Amm Bifluor, thereby making the solution acidic?

Yes. Probably more from bisulfate, as HSO₄^- is much stronger acid than HF.

Is there a name for the acid that is created?

No, it is a mixture, it has no particular name.

[ehanson999]

So if I put this dissociation into a chemical equation form, would it look like this?

?(NH₄)₂(S₂O₈)(aq) + ?(NH₄)(HF₂)(aq)  ?(NH₃) + ?H⁺ + ?(HSO₄)^- + ?F^-

Please correct any mistakes. Like I said, I have limited chemistry knowledge. I know the equation has to be balanced with respect to number of atom and charge. I believe the solution to this would be (in order): 1,1,3,3,1,2. Am I on the right track? Or is there  anything fundamental that I am missing?

Therefore the complete equation would be:

1(NH₄)₂(S₂O₈)(aq) + 1(NH₄)(HF₂)(aq)  3(NH₃) + 3H⁺ + 1(HSO₄)^- + 1F^-

[Borek]

These are two parallel processes, you can't describe them with one reaction equation, you need two separate ones.

Your formulas are slightly off.

Ammonium bisulfate is NH₄HSO₄, when dissolved it dissociates into NH₄⁺ and HSO₄^-, the latter further dissociates into H⁺and SO₄^2- (actually NH₄⁺ also dissociates, into H⁺ and NH₃, but to much lesser extent).

Ammonium bifluoride is slightly more convoluted. Hydrofluoric acid solutions contain bifluoride anion, F-H-F^- (two fluoride anions linked by hydrogen bonds to a single hydrogen). Its formula is sometimes written as NH₄HF₂ and sometimes as NH₄F·HF. When dissolved it dissociates into NH₄⁺ and HF₂^-, again, each of those can dissociate further - HF₂^- can dissociate into H⁺+2F^-.

All first steps of dissociation listed here can be assumed to proceed to the end, then you have a mixture of weak acids, all of them dissociating only slightly and producing quite an interesting acid/base equilibrium.

Not sure what you are aiming at, but it is not an easy system to understand nor to describe (especially with a limited knowledge).

[ehanson999]

Oh, I see. I somehow go the wrong chemical formula for ammonium bisulfate.

The way you have just explained it seems very clear to me. Thank you for that.

We are working toward performing an acid-base titration on the solution in order to see the variation in the concentration of the Amm bifluor in the solution over time.

We have a titration procedure outlined for us (written by an outside party). I have done simple titrations in my chem classes years ago. I am trying to understand the basic mechanisms that are at work when we mix the solution  so that I can better understand how the titration will work.

Again, thank you so much! There's a good chance I'll end up posting more questions related to titration later (under a different question title).

[Borek]

What kind of titration is it?

[ehanson999]

And now I just realized that I misspoke when I originally said "ammonium bisulfate." It's Ammonium Persulfate that we mix with the Ammonium Bifluoride. My apologies...

But if I following what you said earlier about dissociation, then the Amm Persulf would act as such:

(NH₄)₂(S₂O₈)  2(NH₄)^- + (S₂O₈)²⁺

Then I'm sure that may dissociate further; the Ammonium to Ammonia, like you said before. But the Persulfate ion doesn't have any hydrogen to give. Is there a purpose to it being there at all? Or is it just a spectator ion (I think I'm using that term correctly)?

Just saw your most recent post. I'll address that soon.

[ehanson999]

I don't know what kind of titration to call it, other than acid-base. But I can show you what the procedure we have looks like.

This is slightly abbreviated
1) Pipet 1mL sample of the bath into an erlenmeyer flask.
2) Add 9mL of distilled water
3) Add a few drops of phenolphthalein indicator
4) Titrate with 0.1N NaOh to a faint pink color that lasts for at least 15 sec
5) Titrate with 0.1N H2SO4 to remove pink color.
6) Add 40mL of saturated H3BO3 solution, 40mL of reagent alcohol, and 8 grams of KCl. Allow reaction to complete.
7) Add a few drops of Methyl Orange Indicator
Titrate with 0.1N H2SO4 tp faint pink endpoint.
9) Calculation: mL of 0.1N H2SO4 x normality of H2SO4 x 4 = oz/gal of fluoride.

In my experience with titration, one is supposed to titrate to a neutral endpoint. It seems to me that that is accomplished after step 4 or 5. I don't understand the purpose of steps 6-9. If you know, please share. Thanks!

[Borek]

Interesting.

Seems like the idea is to first get to pH as close to 7 as possible, then to react F^- with boric acid to produce fluoroboric acid, and finally to neutralize produced H⁺. Something like

H₃BO₃ + 4F^- BF₄^- + 3OH^-

No idea if it will work as expected (I am not trying to say it won't, all I am saying is I don't remember seeing it. Doesn't mean much).

[Nitishajack]

Both metal oxides and hydroxides are actually correct.

General rule is that, when react with cold water, metal hydroxide is produced whereas oxide is produced if steam is used.

[DrCMS]

Both metal oxides and hydroxides are actually correct.

General rule is that, when react with cold water, metal hydroxide is produced whereas oxide is produced if steam is used.

STOP posting irrelevant rubbish in OLD threads.