Hydrochloric Acid

Hydrochloric Acid
Chemical Formula HCl
Formula Weight 36.46
Equivalent Weight 36.46 (Molar = Normal)
CAS No. 7647-01-0

Hydrochloric Acid is a strong acid in terms of chemical ionization, and solutions of it can be assayed with a standardized solution of 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 Hydrochloric 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. See the indicator list and pH chart in the back of this catalog for details on suitable ranges for various indicators.

A basimetric standard such as Tris(hydroxymethyl)aminomethane can also be used to standardize Hydrochloric Acid solutions. Methyl Red is a suitable indicator.

A 1 Normal solution of Hydrochloric Acid contains approximately 83 mL of concentrated Hydrochloric Acid per liter.