Nitric Acid - a dangerous but very useful tool.

Good old Nitric acid (HNO3) also known as Aqua Fortis or Spirit of Nitre. Nitric acid is one of the acids that are used most often when the fertilizer value is of importance in an end product. Nitric acid is categorized as a strong oxidizing agent, meaning that it does not typically donate its proton.

We all know that any acid has a pH of less than 7. Nitric acid typically has a pH of –1.4 as opposed to vinegar that falls around pH 3. No bonus points for guessing that Nitric acid oxidizes just about anything non metallic to its highest oxidation state. Metals are often passivated, i.e. oxidized to the extent where a corroded layer forms a capsule around the metal protecting it from further oxidizing. Passivation is typically encountered when using concentrated acid rather than diluted acid.

So far so good, where’s the catch…? As with most things in life, there is always a down side to anything. No, we’re not talking about burning holes in your clothes or dissolving your extremities. We’re talking about Nitrous oxides or Nox for short. Whenever you use Nitric acid, the dastardly yellow toxic fumes will be present in copious quantities. If you inhale the fumes, you stand an excellent chance of contracting or aggravating emphysema or bronchitis. Trust an old dog on this one, you do not want to inhale the stuff – ever!

Nox is also classed as being a greenhouse gas under the Kyoto protocol, and with good reason. Nox will react with volatile organic compounds (VOC) to form Ozone which is just as bad for your lungs. Ever heard of acid rain? Nox recombines with water to form – you guessed it – Nitric acid…

Nitric acid is a dangerous acid to work with and it can kill you if you are not careful, yet it is incredibly useful. Combine Nitric acid with Hydrogen Peroxide and you have rocket fuel, combine it with Hydrochloric acid and you get Aqua Regia that will dissolve gold and platinum. Apply a little diluted Nitric acid to wood and you age it dramatically to a beautiful grey gold colour, or add it to your toilet bowl or bathtub to remove those tricky Calcium build-up’s. Nitric acid forms a crucial part of several industrial grade explosives. The list goes on and on, but in practice, we most often use it to oxidize organic materials or combine it with a base to form a specialized nitrate. The most frequent use for us is to effect hydrolysis. This process is called acid hydrolysis, and is used to digest certain organic products into its basic building blocks.

Nitric acid contains around 12% Nitrogen in the concentrations that we use. Good for plants, and even better considering it contains no Sodium or Sulfur.

This is the primary reason that we prefer Nitric acid as a digestion tool when we want to ensure that the end product has value to plants. Yes, it may be slightly more expensive, and yes, it is more difficult to work with than Hydrochloric or Sulfuric acid, but ultimately you end up with an effluent that is good for the soil and valuable as a fertilizer.

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