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Nitric Acid



Nitric Acid
Chemical FormulaHNO3
Formula Weight63.01
Equivalent Weight63.01 (Molar = Normal)
CAS No.7697-37-2

Nitric Acid is a strong acid in terms of chemical ionization and solutions of it can be assayed using a strong base, such as Sodium Hydroxide. The endpoint can be determined potentiometrically or by using a pH indicator. The selection of the indicator used depends on the initial concentration of the Nitric Acid and the strength of the alkali used. This is due to the fact that the Normalities of the acid and the base affect the shape of the neutralization curve that results during the titration.

When both acid and base are 1 Normal in concentration, indicators with effective ranges between pH 3 and 10.5 can be used. Suitable indicators include Methyl Orange, Bromocresol Green, Methyl Red, Methyl Purple, Bromothymol Blue, Phenol Red, Phenolphthalein, and Thymolphthalein.

When both the acid and base are 0.1 Normal, the ideal pH range is reduced to 4.5 to 9.5. Thus, Methyl Orange and Thymolphthalein are not as suitable as the others.

With 0.01 Normal solutions, the ideal pH range is further limited to 5.5 - 8.5.

Some indicators may be oxidized by stronger concentrations of Nitric Acid and therefore it may be advisable to add the indicator just before the anticipated endpoint is reached when the concentration of Nitric Acid is low.

A basimetric standard such as Tris(hydroxymethyl)aminomethane can also be used to standardize Nitric Acid solutions.

A 1 Normal (Molar) solution of Nitric Acid contains approximately 63 mL of concentrated Nitric Acid per liter.

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