Under which criteria HNO3 is a concentrated or a diluted acid?
According to the European regulation on classification, labelling and packaging of substances and mixtures, the classification of nitric acid depends on concentration.

At a concentration of 20 % ≤ c, nitric acid is classified as skin corrosive category 1A. (For a pure substance on the basis of the results of animal testing, this category corresponds to a substance that produces destruction of skin tissue, namely, visible necrosis through the epidermis and into the dermis, in at least 1 of 3 tested animals where responses are noted
following up to 3 minutes exposure and up to 1 hour observation.)

At a concentration of 5 % ≤ c &lt; 20 %, nitric acid is classified as skin corrosive category 1B. (This category corresponds to a substance that produces destruction of skin tissue in at least 1 of 3 tested animals where responses are described following exposure between 3 minutes and 1 hour and observations up to 14 days.)

Furthermore, at a concentration of 65 % ≤ c, nitric acid is classified as oxidising liquid category 3.

Therefore, nitric acid is labelled in accordance with the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) as follows:

Concentration 65 % ≤ c


H272: May intensify fire; oxidiser
H314: Causes severe skin burns and eye damage

Concentration 20 % ≤ c &lt; 65 %

H314: Causes severe skin burns and eye damage

Concentration 5 % ≤ c &lt; 20 %

H314: Causes severe skin burns and eye damage