[jarrick]

Hi all!

I am using Zinc Chloride solution as a soldering flux with 99c solder (99% tin) and am looking for a solution to dip the soldered pieces into afterwards which will neutralise the Zinc Chloride.

The things I am making are stained glass, held together with the solder but I was finding that just rinsing with soapy water was not effective enough at removing all the zinc chloride (which can creep into gaps between the glass and the solder) and so would get corrosion on the solder fairly quick.

I really need something which isn't too noxious to tip down the sink afterwards and that won't leave any residues. I tried making up a solution of ammonia with tap water, to dip the soldered pieces into, and that seemed to work reasonably well (the theory being that any residual ammonia would just evaporate off the pieces) except that when I mixed the ammonia with the tap water, it went cloudy and a white powder would deposit on everything I dipped in it. I don't know what this deposit is but it's a pain to have to clean off (it appears even without dipping anything in) - we have hard water so might be to do with that.

Any ideas are well appreciated.

[Mitch]

I do not have experience in this, but perhaps Windex would work. It is also an ammonia + water solution, but has other surfactants that might help clean the surface.

[jarrick]

the flux manufacturers simply recommend washing with soapy water - do you know if soap or detergent will neutralise the acid of zinc chloride?

Also, I've been experimenting and find that it is the mineral content of the hard water I use which precipitates out when I added ammonia or sodium carbonate (the other base I have at hand) as the solutions were clear when I used de-ionised water. However, when I added a little zinc chloride to those solutions, white solids immediately precipitated out. (not as much with the ammonia solution, loads with the sodium carbonate) which leads back to my main problem of having stuff sticking to my products.

It might be that adding a little detergent will stop it sticking so much, but I'm wondering if there's an alkali I can neutralise the zinc chloride with that only forms water soluble compounds after the reaction?

[Arkcon]

By definition, zinc chloride itself should have minimal acid  If you're using a zinc chloride containing acid flux, then you will need a better rinse.  If there were traces of acids, ammonia should do a good job of making a water soluble neutral salt to wash away.  If you can't get it clean enough with water, ammonia and a touch of detergent, the problem may be more of the flux formula, and not just one possible ingredient.  Wikipedia tells me you can't use zinc chloride flux with delicate electronics work.  So maybe if you found out what flux you can use for electronics, then you'll know what you can use.

[jarrick]

The ammonia and de-ionized water solution definitely has the least amount of precipitate of the two by a long shot - just a pity de-ironized water is so expensive. I was thinking of just testing the water with a ph meter and so adding more ammonia when it started to get acidic - that way I can keep using the solution for longer but something strange has started happening: I added a load of ammonia to the di water and my PH meter is regestering the solution as extremely acidic - all the way to PH 2 (and that was before I added any zinc chloride). I suspect the meter's up the shoot as it's one of those cheap soil testing ones so I've ordered a load of litmus paper.

Is it ok to just keep adjusting the ph value of the same water or is there any danger with doing that too much?

[mcooper1]

A step up from tap water would be distilled water.

As per what else could be done, a sodium nitrate with either a water wash or ethanol wash is doable. Nitrates are soluble in everything according to solubility tables (no issues with the hardness of the water).

[Arkcon]

I'm sorry, but I don't follow your logic.  Why would a person add sodium nitrate, to use as a rinse agent?  Just because most nitartes are water soluble, I don't see where you get "soluble in everything"

[mcooper1]

If I read correctly in plain speak he is looking for something to "remove" and then neutralize ZnCl2 from his product by submerging it in a solution. He has ammonia and bicarb on hand and has only tried these two. Nitrate is relatively cheap. A solution of NaNO3 in water is basic and would remove the ZnCl2 as both of the products are soluble in water. ie: NaCl and Zn(NO3)2 are both highly soluble in water, while the remaining solution is neutral. I don't know specifically what to explain because you are asking a pretty general question but if you would like me to explain a portion of the answer please ask and I will gladly do that.

Edit:

To answer the question of "Just because most nitartes are water soluble, I don't see where you get "soluble in everything"". Good catch, I mis-typed, the nitrate complexes are "always" soluble in water, which is considered a solubility rule in gen. chem.

[Borek]

A solution of NaNO3 in water is basic

Should be neutral by my book.

and would remove the ZnCl2 as both of the products are soluble in water. ie: NaCl and Zn(NO3)2 are both highly soluble in water

ZnCl₂ is pretty well soluble on its own, you don't need to add any other salt to be able to rinse it out.

Besides, neither NaCl nor Zn(NO₃)₂ can be considered a "product" of "the reaction" - there is no reaction occurring other than dissolution of ZnCl₂ (but even that is not necessarily considered a reaction by everyone). You get just a mixture of several dissolved ions, that's all.

[mcooper1]

1.) Sodium nitrate is weak base (pH ca. 9).
http://www.mrdc.com/wp-content/uploads/Sodium-Nitrate-MSDS.pdf

2.) ZnCl2 is a strong acid (pH ca. 2) (Lewis acid by definition)
http://cameochemicals.noaa.gov/chemical/17708

3.) The title of the topic is "looking for a zinc chloride neutraliser".
The reaction between a strong acid and a weak base is assumed to be 100% efficient.

4.) "I really need something which isn't too noxious to tip down the sink afterwards and that won't leave any residues."

-Nitrate will not crash out of the water solution and form insoluble complexes that coat the drains in this case. Every complex (solid complex) it could possibly form is highly soluble in water (ie: NaCl, Zn(NO3)2, ZnCl2, and NaNO3).

-Carbonate will crash out of the solution if DI water is not used (CaCO3 as he stated the water he using is hard).

-And ammonia solutions stink and are relatively inefficient (from my direct hands on experience).

Off topic but, IMO any change in electron density or rearrangement of nucleus in a system is a reaction. Heating a solution up you change the bond length, structure of water, and disassociation constants of water and is a physical change and thus a reaction. Dissolving ions in solution is changing the structure and physical state and thus a reaction. Any gen. chemistry text book with any credibility has tons and tons of problems that say write the chemical reaction for dissolving ZnCl2 solid in water. I do appreciate you pointing out that many do not consider it a chemical reaction though.

[Borek]

1.) Sodium nitrate is weak base (pH ca. 9).
http://www.mrdc.com/wp-content/uploads/Sodium-Nitrate-MSDS.pdf

No, solutions offered for sale by Mineral Research and Development Corp. have pH around 9, that's not the same thing.

2.) ZnCl2 is a strong acid (pH ca. 2) (Lewis acid by definition)
http://cameochemicals.noaa.gov/chemical/17708

I don't see any information about pH 2.0 on the page. Besides, this is nonsense - pH of the solution is not a measure of the acid strength. Yes, pH of zinc solutions is slightly acidic.

3.) The title of the topic is "looking for a zinc chloride neutraliser".

Yes, but OP doesn't look for a neutralization in terms of acid/base reaction, but in terms of removing ZnCl₂ or rendering it inactive so that it doesn't facilitate solder corrosion.

-Nitrate will not crash out of the water solution and form insoluble complexes that coat the drains in this case. Every complex (solid complex) it could possibly form is highly soluble in water (ie: NaCl, Zn(NO3)2, ZnCl2, and NaNO3).

None of substances you listed is a complex, these are all salts.

Any gen. chemistry text book with any credibility has tons and tons of problems that say write the chemical reaction for dissolving ZnCl2 solid in water. I do appreciate you pointing out that many do not consider it a chemical reaction though.

You still don't understand what we are talking about.

A solution of NaNO3 in water is basic and would remove the ZnCl2 as both of the products are soluble in water. ie: NaCl and Zn(NO3)2 are both highly soluble in water

Solution of NaNO₃ mixed with solution of ZnCl₂ doesn't contain "both NaCl and Zn(NO₃)₂ products". After mixing you get just a mixture.