Instructables

How to Test if Fertilizer Has Nitrates in it

video How to Test if Fertilizer Has Nitrates in it
In this video we show you how to test if a fertilizer has nitrates rather than urea or ammonia as its nitrogen source.

The idea is quit simple, in a strongly acidic solution the nitrates will behave like nitric acid and dissolve copper metal releasing nitrogen dioxide gas. Looking for this gas is a strong indication for the presence of nitrates.

WARNING: these reactions produce toxic nitrogen dioxide gas, this must be performed outside or in a fume hood.

To perform the test, simply mix some of your fertilizer with water to dissolve the nitrates and then mix it with hydrochloric acid. Then add in some copper metal.

The reaction is very slow to start up unless you heat it. A nerdy way of heating it on the spot without using a heater is to add a small ball of aluminum metal, don't use too much or it will go out of control. Stir the mixture as the aluminum dissolves to distribute the heat evenly.

After the mixture is heated, place a glass container over the mixture to keep the gases in. If nitrogen dioxide is forming the distinctive brown nitrogen dioxide will fill the container.

What's happening is that in the highly acidic environment (low pH) provided by the hydrochloric acid the copper is reducing the nitrates to nitrogen dioxide gas. This test is specific to nitrates but only works if you have a very high concentration of nitrates in your sample.

And that's how you can tell if there are nitrates in your fertilizer.

If you want to test for ammonia (in case you have ammonium nitrate) just mix some fertilizer with half as much sodium hydroxide and add a little water to cover it. If it starts bubbling and releasing ammonia gas then it contains ammonia.

Don't smell the gas directly, it's not safe. Instead, hold a wet piece of paper over it for a few moments and then sniff the paper. You'll be able to smell the ammonia without gassing yourself.

Note: Yeah i do know that there are hundreds of better tests for these substances. But this method is the simplest i could find that used stuff you could buy at the hardware/plumbing store.

Also, you can't substitute other metals like aluminum or iron because they will tend to produce colorless hydrogen with out without the presence of nitrates. Copper is the best metal to selectively produce nitrogen dioxide from nitrate (gold also works but you have bigger issues if you're trying to test nitrates using gold...)
Biopyro5 years ago
I held my fingertips in some 100% dinitogen oxide in school once, believeing it to be safe. When I removed them my fingertips were completely yellow, which stained the skin until it died naturally! My fingernails were yellow for months although it did eventually fade.
minerug Biopyro5 years ago
On the topic of stains- try silver nitrate This is a silver nitrate stain looks like after ages of scrubbing
DSCN2722.JPG
NurdRage (author)  Biopyro5 years ago
You sure it wasn't nitrogen dioxide? I never heard of dinitrogen monoxide having that particular effect.
Dinitrogentetroxide (NO2 dimer) is what he means.

L
NurdRage (author)  lemonie5 years ago
heh, Pretty awesome class if they had that stuff lying around. :)
On Fridays we were able to carry out our own experiments. I was doing one regarding the amount of copper in pennies, so was dissolving them in concentrated nitric acid. Was pretty awesome!
NurdRage (author)  Biopyro5 years ago
You got to pick your own experiments? You lucky son of gun. It wasn't until grad-school that i could do something of my choosing. At least the current science classes are more interesting than mine.
It did have some purpose - we couldn't just test anything, but were limited to something which we could write a report on, which would give an analysable set of results. I was always led to believe that there was a lot more freedom for mild stupidity like this in the past. It certainly seems to me that kids have a lot less freedom because of health and saftey today than even I did! What age is grad school?
Myyyy mistake! Yeah it was, clearly didn't read throughafter I wrote that.
or, in Florida, you read the label as the law requires a percentage breakdown of each of the five types of nitrogen a fertilizer could contain.
NurdRage (author)  Tool Using Animal5 years ago
yeah, if you're in florida you're all set. A put up this instructable cause someone got some surplus fertilizer wholesale and some moron along the sales chain lost the documentation of what was in it. So the buyer asked me if there was a way to figure out if there was nitrate in it as opposed to urea. I live in canada and nitrogen percentage is required to be listed on fertilizer, but not nitrogen type.
This is good if you don't have the bag. In the US the common fertilizer nitrates are ammonium nitrate, sodium nitrate, and potassium nitrate. You can almost expect one of those to be in chemical fertilizer. The label will list the percentage of nitrogen, potassium, and phosphorous and then tell you what the elements were derived from by chemical name. There are many chemical names in use for the same chemical formula so it is not quite a guessing game but close. The only issue with them that I'm aware of is with ammonium nitrate. The plants will use the nitrogen from the ammonia in preference to the nitrate. That allows the nitrate to leach into the soil and groundwater.
NurdRage (author)  dchall85 years ago
Ah cool, interesting to know. Plenty of fertilizers over here that are Urea based, which have no nitrates. I hear in china that ammonium carbonate based fertilizers are common. I suppose my next task is to figure out a way to detect Urea :)
Bacteria will convert urea to ammonia and ammonia to nitrate, fertilisers get a bit fuzzy when they're in the ground... Have you any thoughts on using biological (bacteria) tests on fertiliser? L
NurdRage (author)  lemonie5 years ago
biological tests would certainly be interesting. But excessively complicated, dirty, or tedious to perform reproducibly. Although if i ever come across a straightforward procedure I'll try to make a video for it.
You know the old nitrate method of urine and horse-manure, bacteria are wonderful things - such as I'm at least thinking about whether I can develop a test of urea. Hmm

L
NurdRage (author)  lemonie5 years ago
oh, you want a test for urea. Now that i think about. There is an analytical chemistry technique where one builds a potentiometric sensor using urease enzymes, a pH electrode, and some chemicals. Can test for urea relatively quickly.
lemonie5 years ago
To more accurately describe the test, you are using copper to reduce nitrate to NO2 - this is what makes it specific to nitrate.

L
NurdRage (author)  lemonie5 years ago
very true, i should have mentioned that part.