3
$\begingroup$

I am not a Chemist or did not learn chemistry as a student. I have faced this phenomena from a natural visualization. So this question.

Experiment: What will be happen if we add a solution of ammonia and water over bad quality iron? When it shall be dried I shall pour again. Several day It shall be done regularly in open nature. Some reaction will take place. Rust will be created on iron.

Here is the main question:

Common people will not see anything significant except rust. But As a chemist how do you understand after three to four days after completion of the experiment that I pour ammonia solution on it? Assume that this three or four days it was in open nature. Something will be produced after reaction except rust. How much of them is water soluble?

$\endgroup$
4
$\begingroup$

In fact metallic Iron doesn't react directly with ammonia. However ammonia can influence the corrosion process because tend to increase the pH. From the Wikipedia Pourbaix diagram (below) you can see which are the products of a corrosion at an higher pH.Of course the pH of you solution depends on the ammonia concentration of your solution (a 1.0 M ammonia aqueous solution has a pH of about 11). enter image description here

Corrosion is in fact inhibited at higher pH, and the products of the corrosion are not specific of the ammonia reaction, so (I think) is hard do identify the presence of ammonia from the corrosion process. Furthermore ammonia is in fact a gas and many of the compounds it forms tend to became ammonia (e.g. ammonium carbonate) and then flow away. However I think that there are many chances that some ammonium salts are produce by the reaction with other species, (e.g. acids) present in the surface of the metal or in the environment. In this case you can look for ammonium ions: $\ce{NH_4^{+}}$ you can identify them with a Ion chromatography or with Nessler's reagent (keep in mind that Nessler's reagent contain mercurium $\ce{Hg}$ so is toxic and not very environmental friendly) that detects even ammonia trace.

$\endgroup$
  • $\begingroup$ Thank you for your answer. So it is not a easy task to identify the ammonia. May I come to the conclusion? $\endgroup$ – Dutta Mar 17 '14 at 12:10
  • $\begingroup$ @Dutta ammonia in a bottle is easy to identify, identify ammonia as a product of a determinate process in an open environment no so easy! You will not have specific products from reaction with iron however if has been used a lot of ammonia some secondary products with other chemical species could be present. If you are going to analyze the soil keep in mind that ammonium ion is a common ion in the soil but maybe confronting adjacent area you could find an increase in the concentration. In this case many other factor like biological activity should be taken in account. Good luck! $\endgroup$ – G M Mar 17 '14 at 12:40
  • $\begingroup$ @Dutta you are welcome! Maybe the simple thing, if there are no restriction in your country, is to use Nessler's reagent I think you can find it on ebay however you should previously perform with this some test at different time interval with pieces of metal you have treated with ammonia to understand if you can have good results. $\endgroup$ – G M Mar 17 '14 at 13:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.