Sulfuric Acid

Sulfuric Acid
Chemical FormulaH2SO4
Formula Weight98.08
Equivalent Weight49.04 (Molar = 2 Normal)
CAS No.7664-93-9

Sulfuric 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 or Potassium 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 Sulfuric 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.

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

When concentrated Sulfuric Acid and water are mixed, a tremendous amount of heat is released due to ionization of the acid. For instance, adding 1 volume of concentrated Sulfuric Acid to an equal volume of water (both at 25°C) results in a temperature rise to over 135°C. Therefore, the acid should always be diluted by adding it to the water. If the water is added to the acid, spattering could result which creates a hazardous situation and the possibility for severe chemical burns. The use of a 1 + 1 dilution of Sulfuric Acid with water (50% Sulfuric Acid) offers a much safer alternative in many instances when the use of Sulfuric Acid is required. For example, when 1 volume of concentrated Sulfuric Acid is added to 3 volumes of water, the temperature rises from 25°C to over 90°C. When the same solution is made by diluting 1 volume of 50% Sulfuric Acid with 1 volume of water, the temperature rises to less than 50°C.

A 1 Normal solution of Sulfuric Acid contains approximately 28 mL of concentrated Sulfuric Acid per liter.

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