What is the shelf life of nitric acid?

Every business or laboratory with a stock of chemicals must keep careful track of their inventory to avoid accumulating degraded or expired chemicals. In particular, a lab manager should be aware of the shelf life of each chemical, as well as ensuring that all chemicals are stored optimally to prolong shelf life. Expired chemicals and degraded chemicals must be disposed of properly in accordance with safety standards.

In this article, we’re tackling one of the seven strong acids, nitric acid. What is nitric acid, how long does it last, and how do you know when it’s past its time?

What is nitric acid?

Nitric acid, or HNO3, is one of just seven common strong acids. It has strong oxidizing and corrosive properties. As a pure compound, it has a colorless appearance, although it may begin to take on a yellowish hue as it degrades.

How is nitric acid used?

Nitric acid has multiple uses in industrial and laboratory settings. Here are just a few of the main uses of nitric acid:

• Substrate for the production of ammonium nitrate fertilizer
• Nitrating agent for dyes and explosives
• Used in organic synthesis, as a building block for nitrogen-containing compounds
• Pickling stainless steel
• Cleaning electronics parts
• Cleaning food and dairy processing equipment of precipitates
• Artificial aging of wood

Does nitric acid degrade?

Yes, it is possible for nitric acid to degrade or break down during storage. A color change is a good indicator of whether your nitric acid has begun to degrade. Pure nitric acid is a clear, colorless liquid. However, during degradation, nitric acid will turn slightly yellowish. This is due to the accumulation of other nitrogen-containing oxides, which will have the formula NOx. This is shown in the following chemical equation:

4HNO3 → 2H2O + 4NO2 + O2

How long does nitric acid last?

The shelf life of nitric acid is generally considered to be in the range of one to three years. This is the expected range for most common chemical reagents. Fluctuations within this range occur as a result of storage conditions. For example, exposure to heat and light will expedite the degradation of the reagent.

Importantly, the shelf life refers to the amount of time that the chemical can be expected to last in an unopened bottle. The expiration date is the amount of time that the chemical will last in an opened bottle. Naturally, the expiration date is often considerably shorter than the shelf life.

Another (often overlooked) consideration for nitric acid is regarding the storage container. Nitric acid is commonly sold in plastic bottles composed of High Density Polyethylene, or HDPE. There is a special grade of High Density Polyethylene that has enhanced resistance to nitric acid. Recall that nitric acid is a strong acid with powerful oxidizing and corrosive properties.

Nevertheless, these bottles eventually begin to degrade when exposed to elements such as heat and light (and plain old time). The date on the bottle considers not only the degradation of the chemical contained, but also the degradation of the storage container itself. Therefore, the manufacturer’s expiration date or shelf-life date should not be overlooked.

How to dispose of nitric acid

If you find yourself in possession of expired or excess nitric acid, proper and safe disposal is critical. Like other strong acids, nitric acid should first be diluted and neutralized to mitigate hazards.

Wearing the appropriate personal protective equipment, and working in a ventilated space such as a fume hood, nitric acid can be first diluted by adding acid to water. It can then be reacted with a base to achieve neutralization. Some options for bases include:

• Sodium hydroxide
• Calcium hydroxide
• Magnesium oxide
• Ammonia
• Sodium bicarbonate

A pH meter or pH paper can be used to monitor the reaction to completion. If the neutralization has been performed correctly, then you no longer have hazardous waste, and you may be able to dispose of your neutral solution down the drain. Always check with the chemical waste disposal guidelines in your local jurisdiction to be sure you are complying with regulations in your area.

Where to restock on nitric acid

Now that you’ve disposed of your old nitric acid, it’s time to restock. Lab Alley is pleased to provide you with the highest quality nitric acid available. We offer small scale to bulk sizing, along with multiple concentration options – so whether your business is big or small, we’ve got you covered. Online shopping and ordering are hassle-free on our website.