faulty nitric acid?

[danieldavies]

hi all. i put 69% nitric acid and distilled water 50/50 in a glass beaker. i put 20 broken up ceramic CPUs in the dilluted nitric and waited and hour. i went to have a look see how the reaction was going, nothing. no colour change, no gold foils floating and all the pins are still on the ceramic. by the way this is at room temperature.
i left it over night, a good 12 hours. when looked this time, there was a slight colour change but not much and only a few of the pins had dettatched from the ceramic.
i tryed heating the reaction to about 50c. waited 30mins. the solution got slighly darker, but there is no brown fumes, no bubbles and nearly all of the pins are still attached.
i let the reaction go at 50c for a few hours. when i looked this time the reaction looked the same as it did a few hours ago. no brown fumes, no bubbles nothing. i'm starting to think that the nitric is very dillute but it says its 69%.
maybe the gold plating is to thick for the nitric acid to attack the base metals?

 

[niteliteone]

What is the temperature of the acid solution you are using :?:

If you are able to heat the solution to around 160*F (71*C) that is where Nitric acid works best for me.

 

[danieldavies]

i'm using a hot water bath. i can get it up to 50*c. the reaction doesn't bubble or give off brown fumes.

 

[niteliteone]

Is this a fresh (new) bottle of Nitric :?:
or is it a bottle you have used in the past, that worked fine, but now does not.
Also how was it stored (ie. closed dark cabinet or in sunshine)

 

[danieldavies]

i have used nitric acid before. it was much more reactive. Even when it was dilluted it would give off brown NO2 when stripping gold foils. the nitric im using now is from a differnet manufacturer. i have only had it in the cupoard for 3 days.

 

[nickvc]

Daniel is it possible that the scrap your processing will not react to nitric. Try a small piece of copper and see if it reacts violently in your nitric if not the acid is dud, if it does the scrap needs incineration and a good hot soak in hydrochloric.

 

[danieldavies]

Daniel is it possible that the scrap your processing will not react to nitric. Try a small piece of copper and see if it reacts violently in your nitric if not the acid is dud, if it does the scrap needs incineration and a good hot soak in hydrochloric.

yes i have tried what you said. there was a slight colour change on the copper's surface but no fizzing or any brown NO2 fumes. it must be the acid, poor quality.

 

[nickvc]

It's the acid then, copper in hot nitric really fumes. Don't know where you got it but send it back and ask for either a replacement or a refund.

 

[niteliteone]

Sounds like the Nitric is not what it's supposed to be.
Read the label carefully and see if it lists the " % " strength. 69% is about as strong as is commercially available unless you specify "Fuming or Red" nitric.
If the bottle shows full strength nitric but the liquid fails, as you have shown above, Then the acid is bad and should be returned for a good exchange.
Take a small glass container with a plastic screw-on lid and a piece of copper with you to test the replacement bottle before you leave the store if you feel they are questionable with their acid sales.

 

[goldsilverpro]

Measure out some of the nitric as accurately as possible, weigh it, and then compute the specific gravity (SG). The SG of 69% nitric acid is about 1.41 at 20 degrees C.
http://www.handymath.com/cgi-bin/nitrictble2.cgi?submit=Entry

For example, assume you measure out 200ml in a beaker and it weighs 280 grams. The SG = weight divided by volume = 280/200 = 1.40

Measurements on a beaker can be as much as 5% in error but usually they aren't. You're not looking for extreme accuracy here. If the nitric is quite weak, this will show it.